graphic organizer and writing assignment radiocarbon dating

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Radiocarbon Dating and Willard Libby Mark as Favorite (7 Favorites)

LESSON PLAN in History , Half Lives , Radioactive Isotopes , ACS National Historic Chemical Landmarks Program . Last updated August 31, 2022.

In this lesson, students will learn about the development and application of radiocarbon dating through an article reading. There are a series of activities to help promote literacy in the science classroom related to the reading. This lesson could be easily used as plans for a substitute teacher, as most of the activities are self-guided.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
• Using Mathematics and Computational Thinking
• Constructing Explanations and Designing Solutions
• Engaging in Argument from Evidence
• Obtaining, Evaluating, and Communicating Information

By the end of this lesson, students should be able to:

• Understand how carbon dating works.
• Learn the concept of half-lives.
• Recognize the factors that contribute to isotopes.

Chemistry Topics

This lesson supports students’ understanding of:

• Nuclear Chemistry
• Radioactive Isotopes
• Carbon Dating

Teacher Preparation : 10 minutes Lesson : Approximate times for students to complete each activity in the lesson:

• Anticipation guide: 10 minutes
• Reading: 20 minutes
• Timeline: 10–15 minutes
• Graphic organizer and writing: 15–20 minutes
• Nuclear equations: 20–30 minutes
• Jigsaw summary: 15–30 minutes
• Reading document and desired handouts to accompany the reading.
• A computer with internet access for the Jigsaw summary.
• No specific safety precautions need to be observed for this activity.

Teacher Notes

Background:

• This lesson plan was originally developed through the American Chemical Society’s National Historic Chemical Landmarks Program . Under this program, ACS grants Landmark status to seminal achievements in the history of the chemical sciences and provides a record of their contributions to chemistry and society in the United States.

Lesson Overview :

The lesson includes multiple components as outlined individually below. The Reading is essential for all of the activities. Teachers can choose to do one or all of the included activities. Student handouts and corresponding answer keys are provided for each item described below:

• Have students identify whether they agree or disagree with the ten statements. After they complete the reading, they can adjust their answers and rephrase “disagree” statements so they read true.
• Ask students to share when they think the method of radiocarbon dating was developed and what technical obstacles the scientist who developed it might have had to overcome.
• After this discussion, invite students to read the article to find more details about how Willard Libby developed the method of radiocarbon dating and how the method can be used.
• Reading : Radiocarbon Dating and Willard Libby
• Students are asked to develop a timeline by arranging events in chronological order. Students could do this before the reading and then adjust the order of events once they read the article and learn more about the discovery of 14 C.
• Students sort artifacts into those that can and can’t be dated using radiocarbon dating methods, then they identify how different kinds of scientists might use radiocarbon dating. Finally, they identify challenges and assumptions that Libby had to make when doing his work.
• Students write nuclear equations for the formation and decay of 14 C and extend that understanding to other types of nuclear equations.
• After reading the article, students work in groups on one of the suggested projects, then each group summarizes their results to share with the class in a 1-minute presentation
• Activity: The Demise of Frosty
• Activity: Why are Some Isotopes Radioactive?
• Activity: Radiological Applications of Isotopes
• Activity: Using Stable Isotopes to Determine Material Origin
• Activity: Graphical Analysis of Nuclear Decay
• Activity: Radioactive Decay and Seafloor Data
• What are Isotopes?
• National Historic Chemical Landmark: Willard Libby and Radiocarbon Dating

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1.42: Radiocarbon Dating and Relative Dating

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• Page ID 9764

• Miracosta Oceanography 101

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Radiocarbon Dating

Radiocarbon dating is one of the most used method of absolute dating because of its useful dating window encompassing the past 100,000 years (it is especially useful for studying archeological features and young sedimentary deposits). 14 C (isotope carbon -14) is a unstable radioactive isotope (radionuclide). Radiocarbon dating (using ratios of the isotopes of radioactive isotope 14 C to stable isotopes 12 C and 13 C derived from buried or isolated organic or carbonate materials. The half life of 14 C [unstable isotope carbon-14] is about 5,730 years . Radiocarbon dating has extensively used in archeological investigation and the study of climate change over the last several hundred thousand years, and precision methods now available make radiocarbon dating highly reliable. Radiocarbon dating is highly effective for extracting ages of organic materials (bone, tissues, wood, etc.) that have been isolated by burial and is effective for dating materials materials from ancient human activities going back for many thousands of years.

Relative Dating

Relative dating is the science of determining the relative order of past events, without necessarily determining their absolute age (see above). Relative dating involved the study of fossils and the correlation or comparison of fossils of similar ages but from different regions where their age is known. Microfossils derived from sediments and cores from wells help in the subsurface exploration for oil and gas. Relative dating is useful and relatively easy compared with absolute dating • Not all rocks can be dated with radioactivity (see above). • This is the way we tell the ages of rock layers relative to each other.

Basic Geologic Principles Used For Relative Dating

These basic principles are easily observed in geologic outcrops, but have value for any number of scientific and technical applications beyond geology. Figure 1.105 and 1-106 illustrates the four laws that are used in resolving the age of rocks and the order in which they formed or geologic events occurred. The three laws are as follows: Law of Original Horizontality —this law states that most sediments, when originally formed, were generally laid down horizontally. However, many layered rocks are no longer horizontal. Law of Superposition —this law states that in any undisturbed sequence of rocks deposited in layers, and the oldest on bottom the youngest layer is on top. Each layer being younger than the one beneath it and older than the one above it. Law of Cross-Cutting Relationships —this law states that a body of igneous rock (an intrusion), a fault, or other geologic feature must be younger than any rock across which it cuts through. Law of Inclusions • An inclusion is a piece of rock within another rock. • The rock containing the inclusion is younger

Radiocarbon Dating and Chronology

Radiocarbon dating is one of most important techniques used by archaeologists throughout the world. Here at Penn State, we are extremely privileged to have an accelerated mass spectrometry radiocarbon dating lab at the Institutes for Energy and the Environment (IEE) Energy and Environmental Sustainability Laboratories (EESL). Our lab fully engages with extensive use of this resource for dating specific materials that facilitate building archaeological and paleoenvironmental chronologies. In addition, we are involved in constructing databases and methodological resources that facilitate using sets of radiocarbon dates as part of meta-data analyses for various purposes including reconstruction of demographic processes, population dynamics, and migration processes over time.

Collaborators

• Dr. Brendan Culleton , Penn State
• Dr. Michael H. Price , Santa Fe Institute

Radiocarbon dating

Vol: 1 (2004) > Issue: 1 (October)

Primer | DOI: 10.1038/s43586-021-00058-7

• NEIF Radiocarbon Laboratory, Scottish Universities Environmental Research Centre, East Kilbride, UK
• Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan
• The University Museum, The University of Tokyo, Tokyo, Japan
• INFN (National Institute for Nuclear Physics) — Lecce Section, Lecce, Italy
• Radiocarbon Laboratory, Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory, Australia
• CEDAD — Centre for Applied Physics, Dating and Diagnostics, Department of Mathematics and Physics ‘Ennio de Giorgi’, University of Salento, Lecce, Italy
• Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ, USA
• Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland
• Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
• Department of Geosciences, University of Arizona, Tucson, AZ, USA
• School of Anthropology, University of Arizona, Tucson, AZ, USA

Radiocarbon dating uses the decay of a radioactive isotope of carbon ( 14 C) to measure time and date objects containing carbon-bearing material. With a half-life of 5,700 ± 30 years, detection of 14 C is a useful tool for determining the age of a

Radiocarbon dating uses the decay of a radioactive isotope of carbon ( 14 C) to measure time and date objects containing carbon-bearing material. With a half-life of 5,700 ± 30 years, detection of 14 C is a useful tool for determining the age of a specimen formed over the past 55,000 years. In this Primer, we outline key advances in 14 C measurement and instrument capacity, as well as optimal sample selection and preparation. We discuss data processing, carbon reservoir age correction, calibration and statistical analyses. We then outline examples of radiocarbon dating across a range of applications, from anthropology and palaeoclimatology to forensics and medical science. Reproducibility and minimum reporting standards are discussed along with potential issues related to accuracy and sensitivity. Finally, we look forwards to the adoption of radiocarbon dating in various fields of research thanks to continued instrument improvement.

Figures ( 0 ) & Videos ( 0 )

Fig. 1 : Life cycle of 14C.

Fig. 2 : AMS radiocarbon analysis process.

Fig. 3 : Calibration curve and precision of calendar ages.

Fig. 4 : Calibration of radiocarbon ages.

Fig. 5 : Bayesian modelling in radiocarbon dating.

Fig. 6 : Radiocarbon dating of sedimentary records.

Fig. 7 : Distribution of 14C in the human body.

Fig. 8 : Radiocarbon analysis of cultural heritage items and detection of forgeries.

Experimental Specifications

Other keywords.

Citations (81)

Associated articles.

• Supplementary information
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• Marzaioli, F. et al. Zinc reduction as an alternative method for AMS radiocarbon dating: process optimization at CIRCE. Radiocarbon 50 , 139–149 (2008).
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Collaborative research reveals how radiocarbon dating can rewrite history in the American Southeast

Stemming from the collaboration between faculty, researchers, and current and former graduate students at the Department of Anthropology, a newly published article sheds light on the importance of radiocarbon dating in the American Southeast, emphasizing its role in refining regional chronologies. Placing radiocarbon dating at the center of collective archaeological practice , born from a graduate seminar taught by Dr. Thompson at the University of Georgia, delves into the challenges and potential solutions associated with the current understanding of chronological frameworks in the region. The collaborative effort, which evolved beyond the seminar, highlights the uneven distribution of radiocarbon dates across time and space in Georgia. The authors argue for the widespread adoption of radiocarbon dating, particularly in cultural resource management (CRM) projects, suggesting its significant impact on creating more accurate chronologies. The article concludes by emphasizing the shared goals across different sectors of archaeology in writing accurate and meaningful histories.

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Radiocarbon dating

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Research output : Contribution to journal › Review article › peer-review

Radiocarbon dating uses the decay of a radioactive isotope of carbon ( 14 C) to measure time and date objects containing carbon-bearing material. With a half-life of 5,700 ± 30 years, detection of 14 C is a useful tool for determining the age of a specimen formed over the past 55,000 years. In this Primer, we outline key advances in 14 C measurement and instrument capacity, as well as optimal sample selection and preparation. We discuss data processing, carbon reservoir age correction, calibration and statistical analyses. We then outline examples of radiocarbon dating across a range of applications, from anthropology and palaeoclimatology to forensics and medical science. Reproducibility and minimum reporting standards are discussed along with potential issues related to accuracy and sensitivity. Finally, we look forwards to the adoption of radiocarbon dating in various fields of research thanks to continued instrument improvement.

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• General Medicine
• General Biochemistry, Genetics and Molecular Biology

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• Radiometric Dating Medicine & Life Sciences 100%
• Carbon Medicine & Life Sciences 50%
• Radioisotope Chemical Compounds 27%
• Forensic Sciences Medicine & Life Sciences 24%
• Reaction Half Life Chemical Compounds 24%
• Carbon Atom Chemical Compounds 23%
• Anthropology Medicine & Life Sciences 22%
• Calibration Medicine & Life Sciences 17%

T1 - Radiocarbon dating

AU - Hajdas, Irka

AU - Ascough, Philippa

AU - Garnett, Mark H.

AU - Fallon, Stewart J.

AU - Pearson, Charlotte L.

AU - Quarta, Gianluca

AU - Spalding, Kirsty L.

AU - Yamaguchi, Haruka

AU - Yoneda, Minoru

N1 - Publisher Copyright: © 2021, Springer Nature Limited.

PY - 2021/12

Y1 - 2021/12

N2 - Radiocarbon dating uses the decay of a radioactive isotope of carbon (14C) to measure time and date objects containing carbon-bearing material. With a half-life of 5,700 ± 30 years, detection of 14C is a useful tool for determining the age of a specimen formed over the past 55,000 years. In this Primer, we outline key advances in 14C measurement and instrument capacity, as well as optimal sample selection and preparation. We discuss data processing, carbon reservoir age correction, calibration and statistical analyses. We then outline examples of radiocarbon dating across a range of applications, from anthropology and palaeoclimatology to forensics and medical science. Reproducibility and minimum reporting standards are discussed along with potential issues related to accuracy and sensitivity. Finally, we look forwards to the adoption of radiocarbon dating in various fields of research thanks to continued instrument improvement.

AB - Radiocarbon dating uses the decay of a radioactive isotope of carbon (14C) to measure time and date objects containing carbon-bearing material. With a half-life of 5,700 ± 30 years, detection of 14C is a useful tool for determining the age of a specimen formed over the past 55,000 years. In this Primer, we outline key advances in 14C measurement and instrument capacity, as well as optimal sample selection and preparation. We discuss data processing, carbon reservoir age correction, calibration and statistical analyses. We then outline examples of radiocarbon dating across a range of applications, from anthropology and palaeoclimatology to forensics and medical science. Reproducibility and minimum reporting standards are discussed along with potential issues related to accuracy and sensitivity. Finally, we look forwards to the adoption of radiocarbon dating in various fields of research thanks to continued instrument improvement.

UR - http://www.scopus.com/inward/record.url?scp=85124591754&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85124591754&partnerID=8YFLogxK

U2 - 10.1038/s43586-021-00058-7

DO - 10.1038/s43586-021-00058-7

M3 - Review article

AN - SCOPUS:85124591754

SN - 2662-8449

JO - Nature Reviews Methods Primers

JF - Nature Reviews Methods Primers

Carbon Dating Worksheet Packet (18 Assignments)

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Learning Objectives

• Identify the age of materials that can be approximately determined using Radiocarbon dating.

When we speak of the element Carbon, we most often refer to the most naturally abundant stable isotope 12 C. Although 12 C is definitely essential to life, its unstable sister isotope 14 C has become of extreme importance to the science world. Radiocarbon dating is the process of determining the age of a sample by examining the amount of 14 C remaining against its known half-life, 5,730 years. The reason this process works is because when organisms are alive, they are constantly replenishing their 14 C supply through respiration, providing them with a constant amount of the isotope. However, when an organism ceases to exist, it no longer takes in carbon from its environment and the unstable 14 C isotope begins to decay. From this science, we are able to approximate the date at which the organism lived on Earth. Radiocarbon dating is used in many fields to learn information about the past conditions of organisms and the environments present on Earth.

The Carbon-14 Cycle

Radiocarbon dating (usually referred to simply as carbon-14 dating) is a radiometric dating method. It uses the naturally occurring radioisotope carbon-14 ( 14 C ) to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years old. Carbon has two stable, nonradioactive isotopes: carbon-12 ( 12 C) and carbon-13 ( 13 C). There are also trace amounts of the unstable radioisotope carbon-14 ( 14 C) on Earth. Carbon-14 has a relatively short half-life of 5,730 years, meaning that the fraction of carbon-14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen-14. The carbon-14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with molecules of nitrogen (N 2 ) and single nitrogen atoms (N) in the stratosphere. Both processes of formation and decay of carbon-14 are shown in Figure 1.

When plants fix atmospheric carbon dioxide (CO 2 ) into organic compounds during photosynthesis, the resulting fraction of the isotope 14 C in the plant tissue will match the fraction of the isotope in the atmosphere (and biosphere since they are coupled). After a plant dies, the incorporation of all carbon isotopes, including 14 C , stops and the concentration of 14 C declines due to the radioactive decay of 14 C following.

\[ \ce{ ^{14}C -> ^{14}N + e^-} + \mu_e \label{E2}\]

This follows first-order kinetics :

\[N_t= N_o e^{-kt} \label{E3}\]

• \(N_0\) is the number of atoms of the isotope in the original sample (at time t = 0, when the organism from which the sample is derived was de-coupled from the biosphere).
• \(N_t\) is the number of atoms left after time \(t\).
• \(k\) is the rate constant for the radioactive decay.

The half-life of a radioactive isotope (usually denoted by \(t_{1/2}\)) is a more familiar concept than \(k\) for radioactivity, so although Equation \(\ref{E3}\) is expressed in terms of \(k\), it is more usual to quote the value of \(t_{1/2}\). The currently accepted value for the half-life of 14 C is 5,730 years. This means that after 5,730 years, only half of the initial 14 C will remain; a quarter will remain after 11,460 years; an eighth after 17,190 years; and so on.

The equation relating rate constant to half-life for first order kinetics is

\[ k = \dfrac{\ln 2}{ t_{1/2} } \label{E4}\]

so the rate constant is then

\[ k = \dfrac{\ln 2}{5.73 \times 10^3} = 1.21 \times 10^{-4} \text{year}^{-1} \label{E5}\]

and Equation \(\ref{E2}\) can be rewritten as

\[N_t= N_o e^{-\ln 2 \;t/t_{1/2}} \label{E6}\]

\[t = \left(\dfrac{\ln \dfrac{N_o}{N_t}}{\ln 2} \right) t_{1/2} = 8267 \ln \dfrac{N_o}{N_t} = 19035 \log_{10} \dfrac{N_o}{N_t} \;\;\; (\text{in years}) \label{E7}\]

The sample is assumed to have originally had the same 14 C/ 12 C ratio as the ratio in the atmosphere, and since the size of the sample is known, the total number of atoms in the sample can be calculated, yielding \(N_0\), the number of 14 C atoms in the original sample. Measurement of N, the number of 14 C atoms currently in the sample, allows the calculation of \(t\), the age of the sample, using the Equation \(\ref{E7}\).

Deriving Equation \(\ref{E7}\) assumes that the level of 14 C in the atmosphere has remained constant over time. However, the level of 14 C in the atmosphere has varied significantly, so time estimated by Equation \(\ref{E7}\) must be corrected by using data from other sources.

Example 1: Dead Sea Scrolls

In 1947, samples of the Dead Sea Scrolls were analyzed by carbon dating. It was found that the carbon-14 present had an activity (rate of decay) of d/min.g (where d = disintegration). In contrast, living material exhibit an activity of 14 d/min.g. Thus, using Equation \(\ref{E3}\),

\[\ln \dfrac{14}{11} = (1.21 \times 10^{-4}) t \nonumber\]

\[t= \dfrac{\ln 1.272}{1.21 \times 10^{-4}} = 2 \times 10^3 \text{years} \nonumber\]

From the measurement performed in 1947, the Dead Sea Scrolls were determined to be 2000 years old, giving them a date of 53 BC, and confirming their authenticity. This discovery is in contrast to the carbon dating results for the Turin Shroud that was supposed to have wrapped Jesus’ body. Carbon dating has shown that the cloth was made between 1260 and 1390 AD. Thus, the Turin Shroud was made over a thousand years after the death of Jesus.

Describes radioactive half-life and how to do some simple calculations using half-life.

The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949. Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby at a seminar in Chicago that year. Libby estimated that the steady-state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, Libby was awarded the Nobel Prize in chemistry for this work. He demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from a series of samples for which the age was known, including an ancient Egyptian royal barge dating from 1850 BCE. Before Radiocarbon dating was discovered, someone had to find the existence of the 14 C isotope. In 1940, Martin Kamen and Sam Ruben at the University of California, Berkeley Radiation Laboratory did just that. They found a form, an isotope, of Carbon that contained 8 neutrons and 6 protons. Using this finding, Willard Libby and his team at the University of Chicago proposed that Carbon-14 was unstable and underwent a total of 14 disintegrations per minute per gram. Using this hypothesis, the initial half-life he determined was 5568, give or take 30 years. The accuracy of this proposal was proven by dating a piece of wood from an Ancient Egyptian barge, the age of which was already known. From that point on, scientists have used these techniques to examine fossils, rocks, and ocean currents; as well as to determine age and event timing. Throughout the years, measurement tools have become more technologically advanced, allowing researchers to be more precise. We now use what is known as the Cambridge half-life of 5730+/- 40 years for Carbon-14. Although it may be seen as outdated, many labs still use Libby's half-life in order to stay consistent in publications and calculations within the laboratory. From the discovery of Carbon-14 to radiocarbon dating of fossils, we can see what an essential role Carbon has played and continues to play in our lives today.

The entire process of Radiocarbon dating depends on the decay of carbon-14. This process begins when an organism is no longer able to exchange Carbon with its environment. Carbon-14 is first formed when cosmic rays in the atmosphere allow for excess neutrons to be produced, which then react with Nitrogen to produce a constantly replenishing supply of carbon-14 to exchange with organisms.

• Carbon-14 dating can be used to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years old.
• The carbon-14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with atmospheric nitrogen.
• One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archeological sites.
• Hua, Quan. "Radiocarbon: A Chronological Tool for the Recent Past." Quaternary Geochronology 4.5(2009):378-390. Science Direct . Web. 22 Nov. 2009.
• Petrucci, Ralph H. General Chemistry: Principles and Modern Applications 9th Ed. New Jersey: Pearson Education Inc. 2007.
• "Radio Carbon Dating." BBC- Homepage . 25 Oct. 2001. Web. 22 Nov. 2009. http://www.bbc.co.uk .
• Willis, E.H., H. Tauber, and K. O. Munnich. "Variations in the Atmospheric Radiocarbon Concentration Over the Past 1300 Years." American Journal of Science Radiocarbon Supplement 2(1960) 1-4. Print.
• If, when a hippopotamus lived, there was a total of 25 grams of Carbon-14, how many grams will remain 5730 years after he is laid to rest? 12.5 grams, because one half-life has occurred.
• How many grams of Carbon-14 will be present in the hippopotamus' remains after three half-lives have passed? 3.125 grams of Carbon-14 will remain after three half-lives.

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NOTIFICATIONS

Radiocarbon dating.

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When an organism dies, it no longer absorbs carbon-14. The C-14 it does contain in its tissues starts to decay at a constant rate.

Name : Radiocarbon dating

Material used : Organic remains such as wood and seeds

Age range : Younger than 60,000 years ago

How it works : Measures the amount of radioactive carbon-14 in the organic remains of living things

Absolute dating methods

Absolute dating methods give rocks an actual date or date range in numbers of years. This interactive explores four different methods used in absolute dating.

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Radiocarbon Dating in Rock Art Research

Fiona Petchey is Deputy Director of the radiocarbon facility at the University of Waikato, Waikato.

• Published: 06 March 2017
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Radiocarbon dating has had a significant impact on rock art research, but an initial enthusiasm for this dating method by archaeologists has been replaced by a degree of scepticism. Radiocarbon dates undertaken directly on rock art or on associated mineral crusts have often reinforced such scepticism, in part because organic carbon-based materials are present in small quantities and their composition is of such variable composition that the technique is stretched to its limits. For the researcher planning to obtain radiocarbon dates, it is essential to have an understanding of the dating options available, limitations of the technique, the potential impact of their own bias, and the value of a dating programme that is fully integrated within a larger project. This chapter outlines the various materials and methods used to radiocarbon date rock art. It includes some recent examples and highlights some advances as well as shortfalls in the dating of rock art.

Introduction

Radiocarbon dating remains the most widely applicable, accurate, and reliable chronometric dating technique available to archaeologists. Radiocarbon (also called 14 C) dating measures the concentration of naturally occurring radioactive 14 C that is formed in the upper atmosphere. 14 C is an unstable, or radioactive, isotope because it contains extra neutrons in its nucleus and, as a consequence, will eventually return to a more stable 14 N isotope by the emission of a negatively charged beta particle. 14 C becomes incorporated into all living things through the nutrients they ingest, and the level of 14 C in a plant or animal is therefore maintained in near equilibrium until an organism dies. The decay rate is considered to be constant, and it is therefore possible to estimate the time since death by comparing the amount of 14 C in a dead organism to modern levels. The technique can date back to around 60,000 years ago, but this varies depending on the material, laboratory, and experimental conditions (for a detailed introduction to 14 C use in archaeology, see Taylor & Bar Yosef 2014 ).

The ability to use 14 C dating was out of the reach of most rock art researchers until the introduction of accelerator mass spectrometer (AMS) dating in the late 1970s. This technique has enabled samples as small as a grain of rice to be routinely dated, which in turn results in minimal damage to the artefact or surface sampled while also expanding the range of materials that could be investigated. Despite this advantage, it was more than a decade beforeHedges et al. ( Hedges, Housley, Law, Perry, & Gowlett 1987 ) and van der Merwe et al. ( van der Merwe, Sealy, & Yates 1987 ) first applied 14 C to rock art. Since then, advances in the AMS technique have enabled ever-smaller quantities (now micrograms) of carbon to be dated routinely, as well as previously untested materials. Such refinements have not been undertaken without considerable effort and associated uncertainty, and critical questions should be addressed by those wishing to demonstrate the reliability of their dates. These questions include: What is the source and nature of the organic material to be 14 C-dated?What is the reproducibility of 14 C values derived from a given sample? And, what is the relationship of that sample to the event in question? Unfortunately, researchers investigating rock art have not always adequately addressed these issues.

In the study of rock art, the identification of exactly what material is being dated is difficult because most samples are small, amorphous, and of uncertain chemistry. Consequently, it can be argued that the most significant recent advances in rock art dating actually fall outside the realm of 14 C, instead focussing on material characterization ( Bonneau, Brock, Higham, Pearce, & Pollard 2011 ; Livingston, Robinson, & Armitage 2009 ; López-Montalvo, Villaverde, Roldán, Murcia, & Badal 2014 ; Mori et al. 2006 ; Vazquez, Maier, Parera, Yacobaccio, & Sola 2008 ). Rather than being driven by the need to demonstrate 14 C reliability, the use of chemical characterization techniques such as gas chromatography, X-ray fluorescence, and Raman spectroscopy has been fuelled by an interest in the provenance of raw materials and the technical processes used to prepare the artworks. The introduction of portable machines with improved detection limits, especially X-ray fluorescence, has enabled the characterization of material in the field prior to sampling ( Beck et al. 2013 ; McDonald et al. 2014 ). This in itself promises greater control and more sample selection opportunities to those investigating the age of rock art. It also highlights the importance of participation by specialists in each specific field of analysis from the earliest stages of sample selection.

The reproducibility and accuracy of rock art dates can also be problematic. Many of the preparation methodologies used to remove contaminants are, by necessity, very general, while others—designed specifically for a particular sample type—are experimental. There is a large body of literature discussing disputed results (e.g., Combier & Jouve 2012 ; Gillespie 1997 ; Nelson 1993 ; Pettitt & Bahn 2003 ; Watchman 1999 ; Valladas & Clottes 2003 ), in part because of the limited amount of (published) information on sampling methodology, location, and sample chemistry pre- and post-treatment, but also because of failure to demonstrate the ability to replicate results with blind and repeated tests ( Gowlett & Hedges 1986 ). Although researchers have only relatively recently started to comprehensively address these issues, it should be stressed that the process for the majority of rock art samples is no more “non-routine” or “experimental” ( Pettit & Pike 2007 :37) than other dating endeavours.

Last, the relationship of the sample to the target event is critical. This is entirely the responsibility of the person collecting and submitting the sample for dating and, by implication, necessitates the researcher understanding the limitations of the preparation methodologies applied. Unfortunately, disassociation between the event and date is the most common form of anomaly between 14 C age and expected age, usually because of the complexity of achieving such a goal when dealing with dynamic and complex contexts ( Taylor & Bar Yosef 2014 :132–136). Whether it is “premature to construct grand schemes or make meaningful generalizations” ( Pettitt & Pike 2007 :28) is open to debate, but this attitude may in part explain the slow uptake of Bayesian methodologies that could enable further refinement of chronologies by rock art researchers.

Relative and Associative Dating

Ultimately, the best way to establish the age of rock art is to utilize a holistic approach that incorporates all dating evidence, both chronometric and relative (e.g., superimposition of art works, stratigraphic sequence, stylistic attributes or diagnostic subject matter, differential weathering and archaeological associations by excavation) ( Aubert 2012 ; Bednarik 2002 ). While this multifaceted approach is commonplace for archaeological investigations generally, these associations are not always obvious for rock art ( Whitley 2012 ), and perceived stylistic relationships, while useful, can be contentious with interpretations limited by our own constructs ( Aubert 2012 ).

Regardless, such evaluation has become a valued component of rock art projects, such as at Nawarla Gabarnmang—a large sandstone shelter in central-western Arnhem Land, Australia, where occupation dates from the past few hundred years to back beyond 45,000 cal bp ( David et al. 2011 ). To provide a robust chronological sequence, Gunn et al. ( Gunn, David, Delannoy, & Katherine 2017 ) plotted patterns of superimposition for overlapping designs found on three ceiling panels by cross-correlating common artistic traits. They were able to combine beeswax radiocarbon dates from the identified micro-layers of superimposed pigment artworks with additional dating information obtained from a panel that displayed a painted motif thought to represent a horse, which would have been unknown on the plateau before ad 1845 (Figure 1 ). Using these relative and chronometric dating methods, three periods were established for the artworks: that older than circa   ad 1430; between circa   ad 1430 and circa ad 1640; and between circa   ad 1640 and ad 1930. This work demonstrated that the recent artistic repertoire at Nawarla Gabarnmang included a number of changes in colour and motif types.

Nawarla Gabarnmang horse motif from Panel D1

An extension of this dating program was undertaken using excavated materials from sediment at the base of the rock art and spalls from the art itself to provide terminus ante or post quem ages for the formation of that art. At Nawarla Gabarnmang, a small fragment of a painted slab was found at stratigraphic levels containing mixed 14 C dates between 21,252 cal bp and 36,270 cal bp ( David et al. 2013 ), and a sample of charcoal-rich ash adhering to the back of the pained rock returned an age of 26,913–28,348 cal bp . To demonstrate the interrelationship of the art and each stratigraphic level, the Nawarla Gabarnmang dates were coupled with a geomorphological investigation of the cave structure. This resulted in a detailed understanding of the relative chronology of roof-fall events, the evolution of the cave, and past interactions of people within the space as they modified the environment. On this basis, it was concluded that the painting itself was made shortly prior to a major roof–fall event and dated to circa 28,000–27,000 cal bp (David et al. 2013 , 2014 ).

Direct Dating

Most rock art dating has been undertaken on black organic pigments of which charcoal is assumed to be the primary ingredient, but a wide range of inorganic pigments can be found, including red, orange, and brown ochre; iron oxides; and black manganese oxide or hydroxide. These can be dated if an organic binder is present in the paint matrix. The interpretation of dates from any material is complicated by the fact that we are not necessarily dating the painting event, but the uptake of 14 C prior to death by the organism used in the paint. In most cases, the difference between the age of the targeted event and that of the material dated is small, but large offsets are possible, as was the case for bird track designs from the Canning Stock Route in the Western Desert of Australia. These designs were expected to date to the time of early nineteenth- and twentieth-century droving activity along the route, but ages of 12,970±270 bp , 12,620±460 bp , and 5520±290 bp suggested to McDonald et al. (2014 :200) that the paints used contained a petroleum-based binder resulting in values that reflected this ancient 14 C source.

Regardless of the material, when selecting samples for dating, it is essential that the extraction of organic carbon and subsequent purification is free from contamination. For rock art samples, this is nearly impossible because of the large surface area, amorphous nature of the paint, and small sample sizes; the researcher has to consider the potential inclusion of fungi, algae, lichens and microbes, insects, rootlets, dust, and soil ( Ridges, Davidson, & Tucker 2000 ), all of which can be found naturally on rock surfaces, while the very presence of humans will often accelerate the growth of a wide range of organisms on the applied paint ( Valladas 2003 ). There is also the possibility of subsequent animal and anthropogenic activity. This can include both ancient (e.g., at Cova Remigia in Spain, where a two-colour paint combination was due to ancient retouching and produced art work that deviated from the more typical monochromatic drawings of the region [ López-Montalvo et al. 2014 ]) and modern activities (e.g., the application of kerosene during modern times to aid photography at Great Gallery, Horseshoe Canyon, Utah [ Chaffee, Hyman, & Rowe 1994 ]). Often the impact of recent, chemically diverse contamination may be complex, and care needs to be taken when evaluating the impact of different contaminants (e.g., burning of tyres could result in either old or young results depending on whether they were manufactured from fossil petrochemical sources or natural modern materials; Steelman, Carrera Ramírez, Fábregas Valcarce, Guilderson, & Rowe [2005 :387] argued that a young age for site M10 at Coto dos Mouros, northwest Iberia, was caused by contamination from burning tyres made from natural rubber products).

Protocols for sampling and reporting rock art dates are well documented (e.g., Steelman & Rowe 2012 :572–573; Watchman 1999 ) and are not repeated here. The primary concern of these authors has been to ensure minimal damage to the artwork while maximizing sample size and the retention of valuable information. These works are undoubtedly useful guides, but the wide variety of datable materials and environmental conditions encountered mean that they can only be taken as a rough indication of what is required. Without prior knowledge of a site, the artwork, and potential contaminants, it is very difficult to sample effectively, as demonstrated by the complexity encountered when dating artwork from along the Canning Stock Route ( McDonald et al. 2014 ). Here, where possible, the sampling strategy included the measurement of replicates from a single motif or superimposed paint layers, as well as rock samples from adjacent unpainted areas to investigate natural levels of organic contamination. Of the “charcoal” drawings sampled, there was only a 53% dating success rate, and few of the collected charcoal samples produced sufficient carbon to enable results to be duplicated adequately or at all (e.g., duplicate samples from a black snake outline at Pinpi 5, in the Jilakurru Ranges, weighing 6 milligrams and 8 milligrams, returned results of 225±40 bp and 470±270 bp , respectively. The large error range on the 8 milligram sample is indicative of extremely low levels of carbon).

Charcoal and Carbon Black

Charcoal is a very popular material for dating. This stems from the fact that it has a high carbon content and is relatively chemically stable. Charcoal dating, is not, however, without issues. Of particular concern when dealing with charcoal, and derivatives such as soot, is the old wood and/or old charcoal effect (also called inbuilt age ) that can add an unknown degree of older carbon into a sample depending on the age of the plant combusted. Related to this is a storage effect by which charcoal or other materials may have been curated for some time before being utilized in the paint ( Schiffer 1987 ). In both cases, the exact magnitude of error is impossible to predict because the impact depends on the age of the art and contaminants. An extreme example of this has been put forward by Combier and Jovue (2012) , who suggested that the addition of fossil carbon in the form of lignite or bitumen caused artificially old ( circa 32,000 bp) dates from Chauvet-Pont-d’Arc Cave in the Ardèche region of southern France. Such a hypothesis can be controversial and difficult to prove either way, in part because of complexities associated with small sample size and contaminant removal that can result in disparate duplicate analyses, but also because of complexities with site interpretation. Indeed, this criticism has been put forward for the Chauvet Cave chronology despite the fact that it has been subjected to an intensive dating regime involving multiple dating techniques, test excavations, and superimposition studies that give confidence to the chronological evaluation ( Clottes & Geneste 2012 ; see also Pettitt & Bahn 2015 ; Quiles et al. 2016 ).

The pretreatment of charcoal commonly involves a succession of ‘acid-base-acid’ washes that vary in length and intensity according to sample size and material robusticity. These pretreatments theoretically remove humic acids (a major organic component of soil made up of a mixture of different acids formed from the decay of plant and microbial remains), carbonates (introduced via groundwater contact with limestone and other carbonaceous sediments), fulvic acids (humic acids of lower molecular weight and higher oxygen content), and atmospheric carbon dioxide (CO 2 ) that has been absorbed onto the surface of the sample. A low-temperature ( circa 300°C) combustion step may also be added to remove the most liable fraction ( Bird et al. 2010 ; Sand et al. 2006 ; Valladas 2003 ). Success is, however, not guaranteed: chemical characterization of pretreated samples has demonstrated that contaminants may remain that cannot always be adequately accounted for ( Alon, Mintz, Cohen, Weiner, & Boaretto 2002 ; Livingston et al. 2009 ).

Most black rock art samples submitted for 14 C analysis are highly amorphous, burnt organic materials of unknown origin. Commonly called carbon black , this terminology hides the fact that this material can originate from a wide variety of sources, including incomplete combustion products of substances such as wood, charcoal, fruit, bone, resins, oil, and fat (also variously termed ‘vegetable or plant black’, ‘ivory/bone black’, or ‘lampblack’) ( Bonneau et al. 2011 ). Such materials are less stable chemically than charcoal and often completely dissolve if routine pretreatment methods are used. Moreover, contaminants, including carbon-containing oxalate minerals (CaC 2 O 4 ) derived from some rock surfaces (see the later section on Mineral Accretions), may become preferentially concentrated in the sample during pretreatment ( Hedges et al. 1998 :36–37).

Many experimental pretreatments have been devised to forgo or minimize these wet chemistry steps. One such technique is plasma-oxidation ashing . This uses a low-temperature, low-pressure oxygen plasma that is excited by an oscillating electric field. The temperature of the gas components is increased by elastic collisions between the electrons and the gas, which result in the electrons becoming sufficiently energetic to break molecular bonds while the gas remains at temperatures below 150°C (see Russ, Hyman, Shafer, & Rowe 1990 , 1991 and Rowe 2009 for methodology). Theoretically, this methodology prevents the decomposition of carbonate and oxalate minerals that occur at the higher temperatures ( circa 800°C) used during more traditional radiocarbon combustion techniques. This process can be used to remove organic contaminants by the controlled reduction of a percentage of the starting mass prior to recombustion at a higher temperature ( Bird et al. 2010 ) or to selectively remove and date tiny amounts of organic binder from the surface of a sample ( Rowe 2009 ). Researchers are divided on the reliability of plasma-oxidation. Steelman and Rowe (2012 :577–578) concluded that replicate measurements on the same image suggested an uncertainty of ±250 years and that their tests were more successful in limestone environments than in sandstone environments. Investigations by Bird et al. (2010) also indicated that plasma-oxidation could not discriminate between similar organic components. This means that the wet chemistry approaches used to remove humics prior to combustion are still recommended if possible (cf. McDonald et al. 2014 ).

One novel approach to removing contaminants was implemented by Bonneau et al. (2011) who used a density separation technique previously used on shells ( Douka, Hedges, & Higham 2010 ) to remove calcium oxalates (density of 2.0–2.2 g/cm 3 ) from black pigments (density 1.5 g/cm 3 ). Although Fourier transform infrared (FTIR) spectroscopy indicated that the black pigment was free from contaminants, the expense of the heavy liquid (sodium polytungstate) and the possibility that the calcium carbonates and oxalates had chemically bonded to the black pigment meant that the technique was not considered to be viable. Experimentation with different preparation methodologies to find an uncontaminated form of autochthonous carbon is sure to continue.

Confirmation of minimal post-depositional contamination using chemical characterization of both the paint and unpainted rock substrateis becoming more common in rock art dating. Bonneau et al. (2011) used both Raman spectroscopy and FTIR to evaluate the presence of calcium oxalates in black, noncharcoal pigments from RSATYN2, a painted rockshelter in the Drakensberg Mountains (South Africa). They evaluated the success of different pretreatments to ensure the removal of calcium oxalate (Raman peak at 1,474 cm -1 ) and gypsum (peak at 1,005 cm -1 ) prior to dating. They were able to confirm by Raman peaks at ~1,360 cm -1 and ~1,580 cm -1 that the samples were typical of amorphous carbon, while the absence of characteristic calcium oxalate (3,600–3,400 cm -1 , 1,616 cm -1 , 1,315 cm -1 ) and calcium carbonate (1,429 cm -1 , 877 cm -1 , and 713 cm -1 ) peaks in the FTIR spectra after pretreatment indicated the success of the acid treatment (Figure 2 ).

Fourier transform infrared (FTIR) spectra of rock art sample taken from RSATYN2, in the Drakensberg Mountains showing progressive contaminant removal after different acid treatments (H 2 SO 4 and HCl) (x: Wavenumber cm -1 ; y: FTIR intensity)

As noted earlier, improvements in analytical techniques have seen the advent of portable systems that enable chemical evaluation in the field prior to sampling. Beck et al. (2013) tested a portable X-ray fluorescence (XRF) elemental analyser and a Raman spectrometer to investigate art from the caves of Villars and Rouffignac in the Dordogne region of France. Although XRF cannot detect carbon directly, the absence of heavier elements such as manganese or iron—which are black and therefore difficult to distinguish from carbon—lent support to the carbon nature of the black pigments and enabled the researchers to isolate and sample scorch marks on the rock surface that are thought to have originated from torches. Raman spectrometry, on the other hand, enabled the detection of organic matter and could be used to separate carbon additions from black inorganic pigments.

Other Inclusions

Inclusions in paints and other dated surfaces (e.g., mineral accretions) are rare, but can include plant fibres, pollen, spores, insects, and microorganisms. Generally, inclusions will originate from a heterogeneous range of processes and sources that are unrelated to the artwork, potentially making date interpretation complex. It is unusual to find undisputed evidence of deliberate additions such as those found at the Yam Camp site near Laura, Australia. Here, Watchman and Cole (1993) recovered a quantity of matted plant fibres mixed with the quartz-kaolinite paint. Typically inclusions are few and careful evaluation of context prior to sampling is essential to ensure no cross-contamination has occurred via contact with visitor’s hands and clothes, or animals ( Bednarik 2002 :12).

Pigment Binders

The dating of non–charcoal-derived binders, including animal fats, egg whites, blood and honey, is highly contentious. These materials often do not survive pretreatment, or indeed environmental conditions, and/or it can be difficult to chemically characterize and distinguish them from contaminants ( Bednarik 2014 :230; Gillespie 1997 ; Livingston et al. 2009 ). Of note is the oft-reported dating of a dark red pigment at Laurie Creek (Northern Territory, Australia)—identified as human blood—that returned a 14 C age of 20,320 +3100/−2300 bp ( Loy et al. 1990 ). Subsequent tests on the sandstone surface indicated that datable organic matter was also present in unpainted areas of the shelter ( Nelson 1993 ), while the small sample size and, in hindsight, processing of the protein using ultrafiltration techniques that are prone to humectant contamination (see Bronk Ramsey, Higham, Bowles, & Hedges 2004 ) could also have contributed to the old apparent age (see Gillespie 1997 ).

Quantitative analysis of these compounds (e.g., lipids, proteins, or carbohydrates) by gas or liquid chromatography mass spectrometry provides greater detail when dealing with complex mixtures of organic materials and has been used to confirm the presence and/or removal of degradation products prior to dating (e.g., Livingston et al. 2009 ; Mori et al. 2006 ). Vázquez et al. (2008) demonstrated the potential of such characterization. They removed two black (manganese and iron oxide) samples from camelid figures at Alero Hornillos 2, Argentina. By isolating lipids using chloroform-methanol and subsequent analysis by gas chromatography mass spectrometry, they were able to identify saturated fatty acids characteristic of degraded animal fats, most probably from a ruminant animal source. While no 14 C dates were obtained, such works hold promise for future avenues of 14 C dating fraction-specific materials.

Surprisingly, beeswax figures are the most commonly dated art media in Australia (~48% of radiocarbon dates obtained on rock art), despite its limited geographic distribution to the northern and western regions of the country ( Langley & Taçon 2010 ). Typically, ‘beeswax’ is a variable mixture of plant resins, gums, and wax. The dating of this material has gained popularity because it is easy to sample and has few interpretative limitations because the age of the wax will approximate the age of creation by bees, it is produced seasonally, and use and collection are concurrent since it becomes brittle and unusable over time. Theoretically, this material is also poorly soluble and is resistant to microbial, bacterial, and fungal growth. Tests on the same sample (BW-4 from the site of Gunbilngmurrung, western Arnhem Land, Australia), but utilizing different preparation methodologies (HCl/NaOH/HCl [ Nelson, Chaloupka, Chippindale, Alderson, & Southon 1995 ] vs. acidified (KMnO 4 ) permanganate [ Watchman & Jones 2002 ]) gave ages 400 years apart (4040±90 bp and 4460±80 bp , respectively). This discrepancy remains unsolved but may be related to differences in sample preparation or to the survival characteristics of the beeswax ( Bednarik 2002 :11). The antiquity of these dates is also anomalous in that most beeswax sampled from northern Australia date to less than 2,000 years ago ( Taçon et al. 2010 :2; Watchman & Jones 2002 :146).

A combination of superimposition studies with the dating of beeswax figures has resulted in a re-evaluation of early European contact events. Taçon et al. (2010) took a total of 10 beeswax samples from the Djulirri art site in the Wellington Range, Arnhem Land, Australia, including two samples from a human figure covered by a yellow/orange emu painting; two beeswax pellets over a painting of a European tall ship; one piece of beeswax from a figure with hands on hips and wearing a hat; two pieces from a snake that overlays a large yellow painting of a prau (assumed to be of a southeast Asian sailing vessel); one piece from a female human-like figure over a white painting of a prau ; a sample from a line that was above both the beeswax snake and over the white prau ; and a sample from an unidentifiable design under the tall ship. The results enabled Taçon et al. (2010) to determine that the painting of the yellow prau was made prior to ad 1664 and was therefore not only the oldest dated contact rock art depiction from Australia, but also some of the earliest evidence for Southeast Asian visits to northern Australia. Similarly, the dates for the beeswax human figure wearing a hat with hands on hips and the painting of the tall ship indicated that a close encounter between local Aboriginal people and Europeans probably occurred in the ad 1700s, much earlier than ad 1818 as presupposed, opening up the possibility of Dutch rather than British contact at this time.

Indirect Stratigraphic Dating

Indirect stratigraphic dating refers to the dating of rock art using materials or objects from above or below the artwork (e.g., laminates such as oxalate skins and calcite [CaCO 3 ] crusts or flowstone and insect nests). Such dating, although not directly related to the painting event, is often used to bracket the age of artworks and is, therefore, often characterized by broad age estimates that are further complicated by the carbon source of the dated materials. It does, however, provide information when there are few other dating options available.

Mineral Accretions

When dating flowstone, it is important to recognize the possibility of the incorporation of “dead-carbon” derived from ancient carbonate rocks, plus any “rejuvenation” that may have occurred: a process by which new carbon can be added to the cave surface through the dissolution and re-precipitation of calcite associated with changes in wet/dry conditions, possibly resulting in younger ages or a mixture of ages ( Plagnes et al. 2003 ). In an attempt to account for such an offset in a nested diamond engraving at Billasurgam Cave in southern India, Taçon et al. (2013) dated what appeared to be a recently precipitated dry shawl of calcite in a nearby section of the cave. The resultant 900 ± 30 bp age indicated the magnitude of offset due to ancient carbon input. This correction was applied to dates on flowstone that bracketed the engraving and resulted in an age that was consistent with similar engravings of Mesolithic age nearby.

Oxalate minerals (whewellite and weddellite) that can form as crusts over artwork or can contaminate carbon samples, as already discussed, can also provide dating opportunities. Oxalates are isolated in the laboratory by treatment in warm, acidified permanganate, which turns the oxalate into CO 2 but leaves carbon from other sources such as amino acids, peptides, and carbonates ( Hedges et al. 1998 ; method reported in Gillespie 1997 ). Therefore, this extraction methodology is more selective than plasma-oxidation or traditional combustion methodologies. Watchman (1987) reported the first dates on oxalate crusts from rockart sites in Australia. The methodology was subsequently improved by isolating individual microscopic layers in stratigraphic sequence to provide additional dating control and limit cross-contamination ( Ruiz et al. 2012 ; Watchman 1993 ; Watchman & Campbell 1996 ).

Most researchers assume that metabolic processes in algae and microorganisms form oxalate minerals, but this remains speculative. Consequently, the age of carbon in these accretions may be near contemporaneous with initial formation or could take place over many years and theoretically could include both rejuvenation and re-deposition of carbon ( Bonneau et al. 2011 ; Watchman 1993 :468; Watchmen & Campbell 196:411). Regardless, calcium oxalate dating can be a valuable tool for confirming chronological limits for pictographs that cannot be otherwise dated directly (e.g., the iron oxide painted “eye-idols” at Abrigo de los Oculados, Spain [ Ruiz et al. 2012 ] or engraved artworks such as at Yiwarlarlay in the Northern Territory, Australia [ Watchman, David, McNiven, & Flood 2000 ]).

Insect Nests

Mud-dauber wasp and termite nests have also been used to provide age-delimiting radiocarbon ages for artwork ( Bednarik 2014 ; Brady, Thorn, McNiven, & Evans 2010 ). Both types of insect gather mud that contains pollen and other organics from nearby environments, and their nests are particularly common in tropical or subtropical locations. In some instances, silica or oxalate minerals that can also be dated may mineralize the nests over time. Often, however, in these instances the interval separating the age of the dating event and the mineralization of the nest may be so great as to be of limited use. This was the case for an artwork dated by Bednarik (2014 :230) at Princess Charlotte Bay, north Queensland, Australia. Here, a silicified mud wasp nest underlay the white kaolinite painted lines of artwork documenting early pearling activities towards the end of the nineteenth century. The resultant 14 C age for organics removed from the nest could only support an age for the artwork sometime in the past 19,000 years!

Date Evaluation: Bayesian Methodologies

The use of Bayesian statistical methodologies for the evaluation of 14 C dates and context is the latest revolution in 14 C dating ( Bayliss 2009 ). The use of Bayesian modelling allows the statistical scatter on the radiocarbon dates to be taken into account, enables the dating to become integrated with archaeological observations, and provides a useful model that can be tested rather than relying on often biased visual inspection. When correctly applied, Bayesian modelling of radiocarbon dates has demonstrably reduced the timescales under discussion (e.g., Bayliss, Bronk Ramsey, van der Plich, & Whittle 2007 ). However, the development of Bayesian models is not easy and requires considerable effort to be expended on simulation and model-building, thus requiring a programme of gradual and progressive dating to infill and test various aspects of the model. Moreover, the radiocarbon dates that constitute these models are tightly linked to pre-existing archaeological opinions (i.e., “prior beliefs”), so, more than ever before, the onus is on the archaeologist to ensure that those beliefs are valid and to recognize these models for what they are—models that require further testing ( Bayliss 2009 :127). Comprehensive guidelines for archaeologists selecting samples for Bayesian evaluation are given in Bayliss (2015) .

The progressive dating methodology and rigorous sample selection protocols recommended by Bayliss ( 2009 , 2015 ) do not mould well with the small sample sizes and complex and often ambiguous superimpositions encountered in rock art. Consequently, most rock art chronologies are still largely based on graphic interpretation of individual radiocarbon-calibrated age ranges. The potential value of Bayesian chronologies has been highlighted by work at the Billasurgam Cave complex, southern India. Here, Taçon et al. (2013) dated five pieces of flowstone associated with an engraving consisting of three interlinked concentric diamond patterns (Figure 3A ). Samples C1, C2, and C3 overlay the engraving, C2 was thought to be younger than C1, and C3 older. C4 was taken from above these, whereas C5 was taken from a surface that was considered to underlie the painting (though about 1 metre away) ( Taçon et al. 2013 :1791). To refine the age of the engraving, the authors then integrated the relative age sequence they had identified into a Bayesian model using the program OxCal ( Bronk Ramsey 2001 ). In the model, sample C5 was designated as predating the engraving and C4 as postdating it. The other three ages were incorporated within a single phase that Taçon et al. thought correlated most closely to the period when the engraving was created. This sequence produced a probable age for the engraving of between 5400 and 5000 cal bp , a significant refinement when compared to visual inspection of the calibrated age ranges of the unmodelled dates (Figure 3B ). 1 However, they noted that C2 produced a very low individual agreement index (A; an index that gives a measure of how well the date fits within the model. The threshold for a good agreement is 60%), suggesting that the date was too young, most likely because of rejuvenation and/or contamination.

Calibrated radiocarbon ages for dated samples from Billasurgam Cave.

Bayesian age model of the results, incorporating the relative sequence information as discussed in the text. Grey = original age distribution; Black = age distribution based on model constraints. TPQ is the acronym for terminus post quem

Radiocarbon dating rock art is difficult; it pushes every parameter of the technique, requiring attention to detail by the archaeologist and the collaborating 14 C scientists. Over the past few decades, a range of processing techniques for rock art dates have been developed, but there is still no consensus on how to handle the diverse range of materials incorporated into these art works, with alternative approaches favoured by different laboratories and researchers. While most studies of rock art recognize the need for replication of dates or comparison of sample preparation methodologies, the science is still hampered by sample size and sample chemistry. Advances in chemical characterization, especially the use of portable technologies and improved analytical detection, combined with the dating of sample-specific fractions, nevertheless promises to open up new avenues of 14 C enquiry.

The relationship of a radiocarbon date to the artistic event of interest is also often difficult to interpret because many dates are of materials that either pre-or postdate the activity in question. While this problem is not specific to rock art dating, the microscopic vertical scale of superimpositions often increases the difficulties of interpretation. Ultimately, researchers must come to terms with the idea that radiocarbon dating does not provide an absolute solution to the dating question; rather, it is a tool from which we can develop chronological models in association with other information gathered from the rock art site.

Acknowledgements

I wish to thank the many collaborators who have given me the opportunity to be involved in a diverse and interesting array of thought-provoking projects, in particular the Jawoyn Association and Margaret Katherine, the senior traditional owner of Nawarla Gabarnmang. Adelphine Bonneau kindly gave permission for the reproduction of Figure 2 . I would also like to thank the editors of the Oxford Handbook of the Archaeology and Anthropology of Rock Art for the opportunity to put forward my opinions and discuss the many issues that should be considered before radiocarbon dating images. Last, but not least, I would also like to give special mention to David Petchey who was my mentor in all things and inspired my interest in archaeology and solving problems.

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This value is further qualified by an associated age offset because of the presence of a possible dead carbon fraction (see text). Taçon et al. (2013 :1792) suggest a conservative terminus ante quem of circa 4100 cal bp .

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Radiocarbon Dating

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This chapter reviews the basic elements of the radiocarbon ( 14 C) dating method and summarizes three generations of 14 C studies in archaeology. It considers in greater detail several major advances in 14 C research including the extension of the calibration of the 14 C time scale into the late Pleistocene, further detailed characterization of Holocene short-term perturbations (de Vries effects), and the development of accelerator mass spectrometry.

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Radiocarbon Dating: Development of a Nobel Method

Radiocarbon dating

Radiocarbon Dating in African Archaeology

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Taylor, R.E. (1997). Radiocarbon Dating. In: Taylor, R.E., Aitken, M.J. (eds) Chronometric Dating in Archaeology. Advances in Archaeological and Museum Science, vol 2. Springer, Boston, MA. https://doi.org/10.1007/978-1-4757-9694-0_3

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Radiocarbon dating the Greek Protogeometric and Geometric periods: The evidence of Sindos

Stefanos gimatzidis.

1 Austrian Academy of Sciences, Austrian Archaeological Institute, Vienna, Austria

Bernhard Weninger

2 Institute of Prehistory, University Cologne, Köln, Germany

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Mediterranean Early Iron Age chronology was mainly constructed by means of Greek Protogeometric and Geometric ceramic wares, which are widely used for chronological correlations with the Aegean. However, Greek Early Iron Age chronology that is exclusively based on historical evidence in the eastern Mediterranean as well as in the contexts of Greek colonisation in Sicily has not yet been tested by extended series of radiocarbon dates from well-dated stratified contexts in the Aegean. Due to the high chronological resolution that is only achievable by (metric-scale) stratigraphic 14 C-age-depth modelling, the analysis of 21 14 C-AMS dates on stratified animal bones from Sindos (northern Greece) shows results that immediately challenge the conventional Greek chronology. Based on pottery-style comparisons with other sites, the new dates for Sindos not only indicate a generally higher Aegean Early Iron Age chronology, but also imply the need for a revised understanding of the Greek periodisation system that will foreseeably have a major impact on our understanding of Greek and Mediterranean history.

Introduction

In contrast to the Near East, where ancient cities often have the form of tell mounds, even the best excavated settlements in central and southern Greece have rarely yielded the long and continuous vertical stratigraphies that in other regions so readily support typo-chronological studies of their material inventories, at high temporal resolution. In Greece, the continuous settlement stratigraphies with well-dated successive layers, that cover many hundreds of years, are a privilege of the ‘northern periphery’ of the Aegean. In this region, dense networks of tell-based settlements developed continuously during the Bronze and Early Iron Age ( Fig 1 ).

Based on free vector and raster map data from @naturalearthdata.com. Constructed with Globalmapper ® Version 11 using Lambert Conformal Conic Projection.

In spite of the steadily increasing number of excavations, in central and southern Greece the Early Iron Age is still better known through cemeteries than settlements. This unfortunate deficiency in Greek archaeology has partly to do with the fact that the architecture of Early Iron Age settlements is indeed often badly preserved, e.g. at Athens and Corinth. Another relevant explanation is that the Early Iron Age settlements have attracted far less archaeological interest, if only because they seldom yield such impressive finds as their contemporaneous necropolises. In consequence, not only is there a general lack of interest in applying radiocarbon dating to the Aegean Early Iron Age, but even the well-excavated settlement sites–suffering as they do from short stratigraphic sequences–are lacking in the main archaeological requirement for high-resolution 14 C-age modelling, which is the availability of an extended sequence of pottery data that would support either quantitative age-depth or pottery-based seriation of the 14 C-measurements. In this respect, and what is sometimes overlooked, even highest-precision single 14 C-measurements on short-lived samples (e.g. from well-defined burial or other contexts) cannot by themselves provide the envisioned high-resolution archaeological chronology. This would require advanced processing of multi-dimensional statistical data (i.e. interdisciplinary research), and ultimately the combination with quantitative pottery data, at best on some kind of metric-scale. Such metric-scaling (alias ‘ quantitative sequencing’ ) is possible, trivially, by direct counting of tree-ring growth-sequences, but also for 14 C-ages that are sequenced according to the time-factor derived from Correspondence Analysis (see below). A particular use of metric 14 C-sequencing is by probabilistic (Monte Carlo) analysis of stratified 14 C-ages from tell stratigraphies, as applied in the present paper [ 1 ] [ 2 ] [ 3 ]. In contrast, when based on ordinal-scaled (‘older-younger’) archaeological 14 C-sequencing, as is the case for the majority of published Bayesian applications in archaeological research, the achieved chronology immediately runs danger of age-distortion due to the uncorrected convolution properties of the 14 C-age calibration curve. As can also be derived from theoretical considerations, the more precise the archaeological 14 C-ages are measured, the stronger their associated artificial age-distortions are likely to become, with actual values strongly depending on the contents of the archaeological sequence in relation to the shape of the calibration curve. A first confirmation for this forecasting is shown in Fig 2 , where the application of Bayesian sequencing to a series of highly-precise 14 C-ages from Assiros [ 4 ] that was measured on bone (N = 27) and combined with the 14 C-ages on two tree-ring sequences has apparently produced an entirely artificial gap of at least 50 yrs length between phases 3 and 4. Presumably, this specific distortion is due to the inhomogeneity of the dataset, hence–ultimately–to the choice of an invalid Bayesian prior. Whatever its cause, the existence of this distortion due to inappropriate age-modelling invalidates the proposed radiometric updating of the Protogeometric vase from Assiros, which is of the very same magnitude. At the other methodological extreme, however, the solution cannot be the (assumed) model-neutral use of calibrated single 14 C-ages, since in this case all that is achieved is repetitive stacking of the one-and-the-same calendric-scale interval, over and over again, with no achieved enhancement of the dating precision. In mathematical terms, the problem at stake is the non-commutativity of the underlying algebra of 14 C-calibration, which complicates the analysis, in both cases, by effectively eliminating the otherwise so advantageous possibility of data-averaging with error-reduction [ 5 ]. The complications of (ordinal-scale) Bayesian age-modelling can be avoided, at large, by application of (metric-scale) stratigraphic age-depth modelling. This will be demonstrated below for the Sindos data.

The modelled probability distributions for Phase 4 and 3 indicate a major hiatus in the stratigraphic sequence, which in reality does not exist.

In Early Iron Age research, if we now switch to the historical perspective, there are further reasons for the general reluctance towards using dating methods such as Radiocarbon or Correspondence Analysis. The main reason is the continuing confidence placed in the absolute dates that were gained by means of textual (historiographic) evidence. In historical terms, this confidence was the outcome of an early enthusiasm and a strong belief in the historicity of the written evidence, and which was eventually (and mainly unintentionally) transformed to become the supposedly scientific base of the now modern Greek chronology. This altogether quite disciplinary tradition in Aegean archaeology contrasts strongly with the highly intense debates on chronology in the Near East. During the last two to three decades, Near Eastern archaeologists, in particular in Israel, have undertaken a wide range of radiocarbon studies, which in many cases have led to the partial or even complete rejection of the authority of the textual evidence. This approach challenges the direct correlation of archaeological and historical data [ 6 ] [ 7 ] [ 8 ] [ 9 ], an approach yet to be customarily pursued in Aegean archaeology.

The historical chronology of the Greek Early Iron Age

The scientific foundation of the conventional Greek Early Iron Age chronology has been, and still is, a much discussed and disputed issue. The beginning of the Protogeometric period, and the tripartite chronological definition of this, as well as the following Geometric period, is based to some large part on highly disputable historical evidence from the eastern Mediterranean. The method to assign absolute age-values to the Greek relative chronological system, which was based on pottery assemblages mostly from tomb contexts, was initially simple: single pottery finds from sites such as Tel Abu Hawam, Megiddo, Samaria, Hama [ 10 ], and more recently Tel Rehov [ 11 ] [ 12 ], were ascribed an absolute date that was obtained by the historical dating of the destruction layers of the respective site they were found in.

While there is practically no evidence that would support the chronological definition of the tripartite Protogeometric period, the transition from the Late Protogeometric to the Early Geometric is unceasingly based on a couple of sherds from a layer at Tel Abu Hawam, which has been variably dated. Similarly, a mere handful of sherds from Megiddo and Samaria has been used to describe, and date, the transitions from Early to Middle Geometric I (850 BC), Middle Geometric I to II (800 BC), Middle Geometric II to Late Geometric (760/750 BC). The same method, already partly used in construction of the Greek periodization by German scholars having worked in the necropolis of Kerameikos at Athens [ 13 ], was firmly established in Classical archaeology, following the comprehensive studies of Greek Protogeometric and Geometric pottery by Vincent R.d’A Desborough and Nicolas Coldstream [ 14 ] [ 15 ].

Aegean archaeology barely took into consideration the continuing discussions in Near Eastern archaeology about the historical dating of at least some of these sites that brought some large ambiguity about the validity of the evidence used in definition of the Greek Early Iron Age chronology. Although some of the eastern Mediterranean sites that yielded Greek pottery have recently also provided long series of precise 14 C-determinations, such as Megiddo and Tel Rehov [ 16 ] [ 17 ] [ 18 ], these sites can still not be taken as safe anchor points for the Greek absolute chronology. This is typically due to the unclear contextual provenance of the randomly discovered Greek pottery finds [ 19 ].

Higher value is often placed on the chronological evidence that derives from the foundation dates of the Greek colonies in Sicily, which are still today widely used as anchor points for the absolute chronology of the Late Geometric and early Archaic period. This was due to an unwavering trust in the credibility of Thucydides, the most respected ancient Greek historiographer, who furnished both the foundation dates of some of the earliest Greek colonies, as well as the potential for correlation of the very same dates with the assumed earliest ‘colonial’ pottery found in the Greek establishments on Sicily [ 20 ] [ 21 ]. Single archaeological finds such as a scarab of the Egyptian king Bocchoris in a tomb at Pithekoussai may support the validity of this method, in certain cases [ 22 ] [ 23 ]. However, unexpectedly ‘earlier’ Greek pottery was soon found to have been used at some of those colonial sites, which was explained as the outcome of ‘precolonial’ contacts. Furthermore, there is still no consensus concerning the actual historicity and the sources of information available to Thucydides, who presents historical data concerning events that took place at least three centuries before his time [ 24 ]. Despite these open questions, the Sicilian evidence is usually considered as safer for the definition of the Late Geometric and Early Archaic periods than the available data from the eastern Mediterranean for the earlier Protogeometric and Geometric periods.

The construction of the relative and absolute chronology of the Greek Early Iron Age, which was the major outcome of Desborough’s and Coldstream’s studies, was not only based on the sequencing of Greek pottery by means of contextual approaches. Also integrated were the results of art historical methods according to the Zeitgeist. A good example, in this respect, is the main argument for the definition of the first part of the Late Geometric that predates the Greek colonisation. This was defined by Coldstream according to the artistic output of a specific Painter, the so-called Dipylon Master: Late Geometric Ia was thought to cover his early work and was therefore given a time span of ten years from 760 to 750 BC. The closely following Late Geometric Ib (750–735 BC) was associated with his late work, with the longer time span of 15 years given, if only to allow for his work together with other painters. While the earlier phases of the Greek Geometric period are based on ambiguous (but: at least) empirical ceramic evidence from the eastern Mediterranean, the beginning of Late Geometric and practically the entire Protogeometric periods are defined according to archaeological intuition [ 14 ] [ 15 ].

Radiocarbon inconsistencies in the Greek Early Iron Age

Unfortunately, the radiocarbon evidence from the Aegean is neither consistent, nor itself sufficiently precise, to support the existence of proposed discrepancies between the historical and the 14 C-based chronological systems. Although there are a number of 14 C-dates from Submycenaean and Early to Middle Protogeometric contexts available at other sites apart from Assiros, e.g. at Kastanas [ 25 ] and Torone [ 26 ] in the northern Aegean, as well as at few other sites in the central and southern Aegean [ 27 ], if we take a closer look at the achieved dating precision (in statistical terms) or otherwise at the sampling and documentation methods (in archaeological terms), the quality of these 14 C-series is insufficient to support further discussion.

The radiocarbon dates of Sindos

The tell mound of Sindos is located some 20 km west of Thessaloniki in northern Greece (40°42’01°N and 22°47’35°E) ( Fig 3 ). This is one of the largest and most complex formed tell settlements in central Macedonia. A settlement system comprising almost exclusively tells developed in the river valleys and coastal plains of this region during the Bronze and Early Iron Age. These settlement sites have the form of conical mounds, known as toumbas in regional archaeology, during the Bronze Age. From the beginning of the Early Iron Age onwards new and larger settlement mounds emerged. They have the form of extended and elevated plateaus that are known as tables. These later tells emerged either independently as new settlement sites or adjacent to older toumbas as means to expand habitation surface.

The two conical structures to the left are modern (photo taken in 2001).

Excavations conducted in the 1990’s and early 2000’s at several parts of the ancient settlement of Sindos revealed long stratigraphic sequences–particularly of the Early Iron Age. These excavations highlighted all major episodes in this tell’s formation: adjacent to an ancient core settlement that initially—during the Bronze Age—probably had the form of a conical tell (toumba), in the following Early Iron Age there emerged not one but two large tells, both with flat surfaces (tables) and both significantly expanding the settlement’s habitation area. Such complex processes in the formation of Macedonian tells, that typically involve extensive levelling and other major earthworks, mainly the construction of extensive terraces made of clay, are not only documented at Sindos, but are analytically presented in the final publication of the excavations, and hence available in all detail necessary for further research [ 28 ].

Complexities in tell formation and depositional history

The formation of a tell mound is a complex depositional process that may hide pitfalls in age-depth modelling due to deep stratigraphic reworking. Sindos presents several characteristic cases of such complex processes in tell formation. For example, the deposition of Late Bronze Age layers immediately below the superficial Late Archaic layers at the top of the toumba may seem puzzling, if someone considers that long sequences of Early Iron Age levels were attested at almost all other parts of the settlement. Apparently debris and layers of this period were missing from the top of the toumba due to continuous levelling works. Furthermore, according to conventional pottery dates, following phase 4 at Sindos we might expect the existence of a major hiatus that dates from the end of the 8 th century BC. Further, since the layers of the immediately overlying phase 3 were deposited after the mid-6 th century BC, acceptance of the conventional dates would imply that a 150 yrs long hiatus marked the settlement history of Sindos during the Archaic period. Below, we will return to our many suspicions that there is something wrong with the conventional historical chronology, when applied to Sindos, and this is evident without application of radiocarbon dating. For the moment, let us begin by analysing the strengths and weaknesses of radiocarbon dating, quite specifically, in the context of a complex tell stratigraphy.

One main concern for application of radiocarbon dating at tell sites pertains to the possibility of stratigraphic reworking of the dated samples. In this respect what immediately comes to mind is the often encountered (upward) reworking of older materials to younger levels. Indeed, since this upward reworking runs parallel to the growth direction of the tell, this would appear the most ‘natural’ direction for the large majority of disturbances. Further, such upwards directional-modelling of tell deposits also corresponds to what may be called the main ‘axiom’ of stratigraphic analysis, that is: the deposits are best dated by their ‘youngest’ inventary. Equally possibly, however, is the stratigraphic re-working in the opposite direction i.e. from younger to older levels, and this would be the immediate (and equally ‘natural’) consequence of the often large-scale and systematic site-management activities of the tell-community. At the Neolithic site of Shir in Syria, for example, some ~45% of all (N = 40) 14 C-dated grain samples from settlement pits have ages 100–200 yrs younger than the 14 C-ages of (incorrectly assumed) ‘contemporaneous’ (i.e. same depth) settlement layers [ 29 ]. Actually, such an unexpected inversion of the more accustomed upwards direction of re-deposition may help to explain one of the major still-existing discrepancies between calibrated 14 C-ages and historical dates. Namely, given the accumulation rate of ~1–2 cm/yr for a typical tell-mound, in combination with the depth of ~1 m for a typical storage pit, such secondary re-deposition of dated materials in younger-> older direction would provide a ‘natural’ explanation at least in quantitative terms for the observed offset of ~100 yrs between the Egyptian historical chronology and the calibrated 14 C-ages from Tell el Daba [ 30 ]. In a nut-shell, resolving such issues is of importance, since enforcing a chronology at fault in one field of research has immediate consequences for other research fields.

Of course, we cannot exclude the occurrence of either sedimentational effects (upwards or downwards) also at Sindos, after having indeed identified a number of possible cases. Nevertheless, it is difficult to imagine that any such material re-deposition would explain all the discrepancies with the historical chronology that we observe at Sindos, and which would allow us to (artificially) maintain its validity vis-a-vis the emerging evidence of its faults (cf. below). Maintaining its validity has consequences, for example, it would imply (ad hoc ) that the (historically dated) pottery sherds and the ( 14 C-dated) animal bones–which show an excellent linear sequence (see below)–would have undergone some kind of systematic vertical separation, in the order of ~1 m, but for which there is no presently ascertained physical or cultural process. The point hereby is that, even if there did exist some unrecognised (say ~1 m deep) storage pits, and even if these pits were in-filled from above, this would not affect the original association of the (historically dated) pottery sherds with the ( 14 C-dated) animal bones. The same argument would apply, similarly, even for the alternative case that the pottery and bones do not derive from some unrecognised deep-storage pit but from some other of the many types of tell-management deposits. We may expect the original association of pottery and bones to remain intact, under the large majority of depositional conditions, unless we assume the existence of some material-discriminating physical or cultural process that would act differently for sherds and broken bones (but which is unlikely, as noted above, if only with the exception that dogs seldom eat sherds). Another point-at-stake is that–in clear contrast to the aforementioned case of Shir–the 14 C-data at Sindos do not show any unusually wide spread of 14 C-ages, that would be indicative for the postulated inter-level (or inter-phase) sample movement.

Nonetheless, an important issue in age-modelling is to critically contrast the primary (sedimentological) site-formation processes with the (cultural) definition of settlement-formation according to archaeological phases/periods. Inevitably, the sedimentological sequence of layers will seldom find a match in the temporal sequence of phases/periods. At Kastanas, for example, a site in close vicinity to Sindos, some buildings were destroyed only a few years or decades after erection, whereas others (e.g. level 12) have a life-span of more than a century before being levelled for purposes of rebuilding [ 31 ]. In contrast to the applied linear age-depth modelling, at Sindos the actual tell-formation is indeed (possibly) not well-represented as series of continuous, successive, and equilength sedimentological episodes.

Sampling methods and strategies

Despite all complexities in tell formation, archaeological exploration at such settlement sites is often accompanied with the welcome opportunity of working with successive destruction layers, that have clearly distinct ash and other burnt materials covering well preserved artefacts on surfaces of use. The house-floor assemblages that were found directly beneath thick layers of ashes and collapsed walls do not necessarily provide direct comparisons with the Pompeii-like systemic inventories that have both rapid and abrupt depositional qualities (Pompeii premise). They may nevertheless be taken as assemblages of artefacts, archaeobotanical and faunal material that were deposited and probably also used in the same period. At Sindos, such near-ideal stratigraphic conditions for radiocarbon sampling are given in a number of instances. An example is the fire-destruction of phase 7, from which six short-lived bone samples were sampled (cf. Table 1 ).

Although a reconstruction of the Early Iron Age settlement plan is not possible at Sindos, as at few other Aegean Geometric sites such as Zagora, Sindos offers the unique opportunity for studying the Aegean material culture by means of a 13 m deep stratigraphy, which shows more than 16 settlement phases, at least 13 of which are successive ( Fig 4 ). The large amount of pottery from its stratified contexts allows the comparative study of several Aegean pottery styles, in a region where pottery sequences of the Early Iron Age have until now been known almost exclusively by means of burial contexts. The finds from Sindos include non-local ceramic wares from many different Aegean micro-regions, such as Euboea, Attica and Corinth, and of course Macedonia. Regional correlations between the chronologies of the central and southern Aegean were already developed by Coldstream, as demonstrated in his most influential book on the Greek Geometric Pottery [ 15 ]. At that time any synchronization with the northern ‘periphery’ was still unthinkable. The Greek relative chronological system still suffers from all biases and ambiguities that resulted from its construction by means of burial contexts given that evidence from stratigraphies was practically missing. The fact that the inhabitants of this Aegean gateway to the Balkans made use of pottery from several parts of central and southern Greece makes Sindos a most appropriate place to achieve a major geographic expansion of the Aegean Early Iron Age relative chronology, and this now applies–due to its many Aegean contacts–to essentially the entire Mediterranean (see below).

An additional benefit of the long stratigraphy at Sindos is that it allows the newly developed Early Iron Age pottery chronology sequence to be dated by a series of N = 21 short-lived 14 C-samples, that were all measured to high-precision (σ < 25 BP) by the Mannheim 14 C-AMS laboratory (Lab-Code MAMS). The series covers essentially almost the entire cultural sequence of the Aegean Early Iron Age, beginning with Late Protogeometric, through Early Geometric I and II, Middle Geometric I and II, up to the Late Geometric Ia and Ib ( Table 1 ).

All 21 samples of animal bone for the radiocarbon analysis were taken from good and relatively well-dated contexts at the stratigraphic trench A.0 that was excavated from 2000 to 2002 at the south-eastern side of the high table. The successive layers sloping to the south on this trench’s profiles reflect long process of debris accumulation at that side of the Early Iron Age table ( Fig 4 ). While some of the earliest excavations at Sindos were conducted with the method of arbitrary layers, the most recent trenches including trench A.0 were excavated with the method of single context recording. Nevertheless, there is no archaeological procedure (known to us) to determine whether bones from allegedly ‘undisturbed’ contexts could be residual from earlier layers, or not. Such re-depositional processes may however be traced by means of pottery , especially in assemblages that have been statistically and typologically studied in such detail as those of Sindos. From these studies we know, for example, that the floors and contexts at trench A.0 of Sindos, where the animal bone samples were finally deposited, did not yield any noticeable residual ceramic or other artefacts.

The sampled bones of domestic animals (oxen/cows, pigs, sheep/goats) come from six successive phases of the settlement (phase 11 to 6) that date according to the conventional relative chronology from the Late Protogeometric (950–900 histBC) to the Late Geometric Ib (750–735 histBC). Note that samples were purposely also taken from phases 6, 7, and 8, despite the threatening expectation that their 14 C-ages would have readings on the Hallstatt plateau (~800–400 calBC) of the 14 C-age calibration curve.

The two latest samples were collected from the floor of a house of phase 6. Two of the six bones analysed from phase 7 were collected from the floor below the collapsed mudbrick wall and the roof of an earlier house. The other four bones of the same phase were found in contexts mixed with burnt material from the same house close to this wall. A thick layer of ash containing burnt clay probably from a house roof was covering the three bone samples together with other artefacts that were found on a floor of phase 8. Part of this destroyed settlement phase was levelled with debris that may have been brought from another part of the contemporary settlement. In any case no samples were collected from that context. The three bone samples from phase 9 were collected above the surface of a thin layer of yellow clay that used to cover the debris of an earlier phase and formed a new surface of use. All four bone samples of phase 10 were collected just above and within two successive thin layers of black earth that represent surfaces of use and relate to them. These were well-defined contexts that contained burnt material and large quantities of pottery and sea shells close to a wall that used to support a layer of yellow clay (terrace). The two sampled bones from phase 11 come from a similar context. This was a burnt layer with a lot of pottery and sea shells deposited on the surface of use, close to a massive and better preserved terrace wall. A more detailed description of the contexts of the bone samples can be taken from the section profiles and plans, which are available and analytically commented in the final publication of Sindos’ excavations [ 28 ].

To complete our brief review of the excavations, we note that the archaeozoological as well as archaeological material from the excavations at the settlement of Sindos is stored within the facilities of the Ephorate of the city of Thessaloniki. All necessary permits (ΥΠΟΠΑΙΘ/ΓΔΑΠΚ/ΔΣΑΝΜ/ΤΕΕ/Φ77/164609/3721) were obtained by the Greek Ministry of Culture for the described study, which complied with all relevant regulations.

Introduction of the Sindos 14 C-data

Based on minimal age-modelling (i.e. albeit model-neutral, but not distortion-free; cf. below), Fig 5 provides an overview of the contents of the 14 C-database ( Table 1 ). In joint context with the INTCAL13-calibration curve and the high-precision laboratory data used in INTCAL-13 construction, Fig 5 shows the 14 C-histogram and the summed calibrated 14 C-age probability distribution of the summed Sindos data (N = 21), both in context with their individual BarCode-ages (small vertical lines on the calendric time-scale). The applied numbering of samples and Sindos-phases is useful for first screening of potential outliers (cf. Fig 5 , lowest line), but this is more efficiently achieved by stratigraphic (metric) age-depth modelling (see below). The Barcode-ages are pragmatically defined as central values of the 95%-confidence intervals. For this kind of data-representation, aimed only on achieving a first summary of the overall data spread, it is important to note that the calendric-scale position of the barcodes is practically always strongly offset, in relation to the (unknown) calendric age. The horizontal age-distortion of single 14 C-ages can be quite strong, in all variables (i.e. not only those evident in this graph), and is typically in the order of– 100 to + 100 yrs, but often more. This distortion is often only attributed to the existence of multiple calibration curve readings. However, from a more fundamental mathematical perspective, there are many such effects (including e.g. the decadal-scale clustering of Barcode-values, as can be taken from Fig 5 ), and all caused by one and the same factor, that is the non-commutative probabilistic algebra that is underlying the statistical properties of the 14 C-age calibration curve. As goes for the present Sindos-series, the strongest age-distortion applies to the youngest date (ID2, MAMS-27019: 2552 ± 23 BP). This is easily recognisable, both from the extreme length of its error-bar as well as from the strong age-shift of the corresponding Barcode-line. Note that, in Fig 5 , in order not to clutter up the picture, we have decided to show the error bars only at 68% confidence.

As goes for the Hallstatt Plateau (~800–400 calBC), an essentially flat region of the calibration curve that archaeologists prefer to avoid, it has its cause in the chance compensation of the increase in the natural atmospheric production of 14 C and its decrease due to radioactive decay in parallel to its oceanic uptake. In consequence, when samples are taken from this time-window, by conventional wisdom all 14 C-ages for the Middle Geometric II (800–760 histBC), Late Geometric Ia (760–750 hist BC) and Late Geometric Ib (750–735 histBC) would be expected to give the same 14 C-age of 2480± 30 BP. As it turned out, none of the samples from Sindos have this 14 C-content ( Fig 5 ), with the exception of the obviously only quasi-distorted sample ID2, from the very youngest 14 C-dated phase 6 at Sindos. Knowing that phase 6 follows immediately after phase 7, from the intercept of the 14 C-age for ID2 with the INTCAL13 curve we can immediately provide a most precise (first) estimated reading of 780 ± 25 calBC for this phase. This is confirmed, later, by the explicit age-modelling (see below). Going back in time, all nine samples from phase 7 and phase 8 came from layers that were destroyed by fire, as evidenced by the large amounts of ashes, charcoal, and collapsed mud brick walls on the settlements floors. Even such apparently ‘safe’ contexts, however, do not entirely eliminate the possibility that some of the animals, whose bones were deposited in these two (or any of the other settlement phases), may actually have been consumed in an earlier phase. There are however reasons to think that such biases are less possible to have affected our sampling (see above).

Stratigraphic 14 C-based age-depth modelling at Sindos

For age-depth modelling at Sindos we have applied the method of Gaussian Monte Carlo Wiggle Matching (GMCWM or GaussWM) [ 2 ]. The achieved chronological results are shown in Fig 6 , with corresponding modelling uncertainties shown in Fig 7 . The numeric modelling values are provided in Table 2 . Before continuing with the archaeological discussion of these results, let us take a moment to evaluate the applied method itself. In historical perspective, GMWCM is an extended and today largely automated version of the wiggle-matching method that was first introduced in the year 1986 by Gordon Pearson in support of the (preliminary) dating of floating tree-ring chronologies based on matching a series of 14 C-ages to the calibration curve [ 32 ]. Also in 1986 essentially the same (Chi-squared) method was applied to stratified 14 C-ages from Tell Dipsis (Bulgaria), Niederwil (Switzerland) and Arslantepe (Turkey), as well as to historically seriated 14 C-data from the Egyptian 1 st Dynasty [ 33 ]. An important drawback of these earliest applications, however, was the difficulty in determining the statistical uncertainties of the dating results, but which can be overcome by including a Monte-Carlo simulation of the different error sources [ 34 ]. Hence, despite a steadily increasing number of extensions and modifications applied over the years (e.g. [ 1 ] [ 2 ] [ 3 ] [ 34 ]), the GMWCM-procedure is still today based on essentially the same method as it was, some 30 years ago. As illustrated (schematically) in Eq (1) , the approach taken is to minimize the statistical distance (on the 14 C-scale) between the discretely measured sequence of tree-ring (or archaeological) samples that have 14 C-ages D i ± σ(D) i [BP], but unknown calendric ages, and the continuous (e.g. splined) calibration curve that has 14 C-ages K(t) ± σ(K) i [BP]) at certain known-age calendric years t.

The samples are arranged in stratigraphic order, with stratigraphically highest (‘youngest’) sample (Hd-27019) at table top, and stratigraphically lowest (‘oldest’) sample (Hd-27034) at table bottom. The Monte Carlo results are provided with measured marginal uncertainties (noted at 95%-confidence), without numeric rounding. During run-time, a Gaussian-shaped random error of ± 10 [a] was added to the numeric age of each sample derived from the (itself randomised) depth-position. The intention hereby is to include not only (possible) phase-internal but also phase-overlapping sample re-location. Note that, due to the Monte Carlo procedures, the overall dating results are given, not for each sample ( per se ) but for the associated stratigraphic sample position. Further quadratic addition of 20 yrs error (95%-confidence) to each of these stratigraphic positions would appear advisable, to account for unrecognised error components, but which cannot be proven to exist.

Accordingly, there exists a statistically best-fitting year t, not only for 14 C-ages measured on tree-ring series (as in the application by Gordon Pearson), but similarly for many other kinds of seriated, sequenced, or otherwise stratified sample series. All that is needed is that the series has a temporal structure (call it an ‘age model’). Potential applications for the required age-modelling can be based on known (metric-scale) historical time-spans, as for the Egyptian historical chronology mentioned above, but also on sequences of ordinal-scale (older/younger) settlement phases. The method is also applicable to archaeological tell-stratigraphies, as in the present paper, in which case the age-modelling can be based on the measured (metric-scale) stratigraphic sample depth. The special advantage of applying the χ2-method to metric-scaled sample sequences is that the required numeric modelling values are immediately available (as measured depths) and forthwith only require rescaling (depth->age). Of course, in practical applications, the necessary depth->age rescaling requires a fair amount of statistical processing (cf. below). But, from a mathematical viewpoint, there are only minor differences between the different Chi-squared approaches. For example, whereas in dendro-studies the distances between the 14 C-dated (annual growth) samples have small sampling errors (0–2 yrs), in archaeological studies the distances between dated samples can be quite large (for settlement phases: 10–50 yrs). This makes the necessary modelling estimates, in archaeological studies, inherently much more error-prone than in the dendrochronological application. In consequence, although archaeological GMWCM-studies require no fundamental change in the mathematical algorithms, they do require further attention in terms of error analysis. Next to such technical aspects, the really important advantage of applying GMWCM to tell-stratigraphies (e.g. Sindos) is that the validity of the modelling assumptions can be checked, namely, by direct comparison of the model-ages achieved for each sample, with the results based on the respective (unmodelled) single calibrated 14 C-ages. This also applies vice-versa .

Nevertheless, although in concept simple, the advantages of metric age-modelling are not received for free. Rather more, the application of metric modelling to real archaeological data is immediately complicated by the need for more advanced (and higher quality-level) requirements already during archaeological sampling, and similarly during the statistical data processing, hereby in terms of data input/output procedures, age-modelling algorithms, application of randomization requirements, calculation of probabilities, and graphic output routines. In the course of the methodological extensions of the GMCWM-method described in [ 29 ] [ 34 ], today the technical procedures are largely automated.

The application of GMCWM to the Sindos 14 C-series is illustrated by a screenshot ( Fig 8 ) of the most recent GaussWM-dialog, which is integrated in CalPal-software (Version 2020.2). In terms of hardware, the results were obtained using workstation Celsius W530 ® with Xeon E3-1281v3 ® 3.7 GHz CPU. In terms of software, CalPal is written in programming language Fortran 95, with compilation by Intel ® Parallel Studio XE Fortran Compiler, in combination with Winteracter ® 13 and IMSL6.0 ® libraries. Data transfer in Excel © -format is achieved through the ODBC © -Interface (Open Database Connectivity). Such ODBC-compliancy greatly simplifies the analysis of archaeological 14 C-data, due to the possibility of user-convenient external data-editing.

Left : spreadsheet with input of data and results; program functions; tools for age-model construction; tools for statistical analysis. Right Upper : Graph showing on-screen (Monte Carlo run-time animation) the presently achieved best-fit position of the archaeological 14 C-series in context with the selected calibration curve. Right Middle : Histogram showing the dating probability and precision of the step-wise expanded 14 C-series. Right Lower : Statistical fit parameters are given as run-time series of the stepwise expanded sequence. Red = dating probability; Blue = dating precision; Green = simultaneously optimized precision and probability. Note: During run-time the GaussWM tables and graphs are continually refreshed (every ~3 secs). An explorative model analysis requires ca. 1–5 min run-time. Typical runs require 6–16 hours.

An important amendment of the GMCWM procedure, used in the Sindos-analysis, is the application of a refined data/curve fitting method, based on the non-central Chi-squared distribution instead of Chi-squared. This does not change the GMCWM results, but makes the analysis less sensitive to slightly asymmetric 14 C-data, as may be caused by chance, or small (decadel-scale) 14 C-reservoir deviations and interlaboratory offsets. The use of non-central Chi-squared probabilities require calculations of the incomplete Gamma function, which were conveniently performed (in Fortran 95) by a call to the IMSL ® -subroutine CSNDF. The advantage of using CSNDF, in comparison to GAMMQ, is that allows passing of a variable noncentrality parameter λ. In the Sindos analysis we applied λ = 5 (for λ = 0 CSNDF converges to a Chi-squared test). As shown schematically in Eq (2) ) the calculation of best-fitting probabilities based on CSNDF follows directly after the Chi-squared distance calculations.

Run time parameters

The final Sindos results are based on a GMCWM run with the following parameters and program settings. The model was run for a total of 1000*50*60 = 3*10 6 random iterations. These included, (1) a fixed number of 60 steps in the sequence expansion, (2) a number of 50 Monte Carlo iterations for phase-internal re-ordering, and (3) a total number of 1000 complete run repetitions. In effect, therefore, the modelling results shown in Table 2 (Column: Results ) are based on 1000 independent measurements., each of which was obtained as best-result of an extended search. During run-time, in parallel to the phase-internal randomized sample order ( Table 2 , Column: Random Depth Position ), the sample distances were also randomized, with additional (squared additive) Gaussian calendric-scale distance errors set to σ = 10 yrs ( Table 2 , Column: Random Age ). Finally, as a final error component, applied prior to each model-expansion, the calibration curve (INTCAL13) was re-splined, with the new curve in each case based on the original INTCAL13 raw data, but re-measured with Gaussian 14 C-scale errors set to σ = 10 BP. The run-time of the final Sindos age-modelling run was 16 hours.

In a nutshell, the best-fitting position of the Sindos 14 C-data series on the INCAL13 calibration curve (shown in Fig 6 ) was identified by systematic stepwise linear-expansion of the sample sequence. The applied linear-stratigraphic age-model was constructed according to the measured sample depth. The validity of this age-model, with modelling errors in der of range of 10–20 yrs (95% confidence), is confirmed due to the reproducibility of the chronological results when only the single 14 C-ages are used i.e our interpretations are altogether independent of the assumptions (whether critical or not) that are at the base of the age-depth modelling. The modelling results are nonetheless useful. They allow the derivation of a simple linear equation, as shown in Fig 7 , that conveniently supports the dating (with associated errors) for any requested tell-depth.

Although the main aim of GMCWM in stratigraphic studies is, naturally, to identify the best-fitting length and age-position of the 14 C-dated sample sequence on the 14 C-age calibration curve (here: INTCAL13), what is actually challenging–as mentioned above—is the derivation of (albeit) realistic dating errors. Of special interest, in this respect, is to derive the marginal probabilities that are assigned (here) to the different Sindos phases. In the present GMWCM–application to the Sindos data, as it turns out, the (calculated) marginal dating uncertainties are quite small (annual-scale) for the youngest phases (7 and 8), but increase strongly for the older phases ( Fig 7 ). Understandably, this is the immediate consequence of the shape of the calibration curve in the time-window under study (1100–700 calBC), which shows a rather wiggly section for ages 1100–800 calBC, followed by a major increase in slope, if only for some 20 yrs (~800–780 calBC). Lucky are those archaeologists, in terms of achievable supra-precision, whose 14 C-dated samples have readings into this time-window. Yet, this time-window–wide as it may appear ( Fig 5 )–is narrower than it looks (from a statistical perspective), as well as representing a most strongly wobbling target (from the view-point of tell-related sedimentation processes).

Note that, with this intention, we must foremost (quantitatively) allow for possible stratigraphic reworking of samples. In the present application, this is attempted both by controlled intra-phase Monte Carlo randomization of the stratigraphic sample position (for multiple-dated phases i.e. phases 7–10), as well as by Gaussian inter-phase spreading of samples, for all phases. Whereas the Monte Carlo randomization is achieved by application of a random-position algorithm only to samples from the multiple-dated phases, the Gaussian sample spreading is achieved by applying an additional (depth-controlled) Gaussian age-distribution, with chosen width of ± 10 yrs (68% confidence) to all sample depths. Even under such, at least, intentionally realistic Monte Carlo conditions, what we actually observe for the younger phases are calculated dating uncertainties smaller than 10 yrs. Given that 14 C-AMS interlaboratory offsets are presently estimated to have values of ± 10 BP, at best, we have accordingly enlarged the calculated errors to this value (on the calendric time scale: ± 10 yrs) for all phases. Nonetheless, Figs ​ Figs6 6 and ​ and7 7 show the original (uncorrected) uncertainty values, if only for purposes of critical interrogation. Put differently, we believe we have the reserve in dating caution that is necessary for targeting the window of supra-high dating precision, as noted above. However, what is equally if not more critical to demonstrate is the stratigraphic integrity of the 14 C-dated samples, and this in combination with the archaeological finds. To this aim, on the following, we provide a detailed archaeological description of the site. Our focus is on the pottery inventory, which is to be used for wider synchronisms, and which is presented in a phase-by-phase manner, from old to young.

Relative pottery-based chronology at Sindos

The relative chronology of the stratigraphic sequence at Sindos was achieved after some quite exhaustive statistical, typological and technological analysis of its large pottery assemblage that comprised 4897 rim-sherds and numerous other wall and other fragments from well-stratified contexts. The study of pottery technology took place independently from its typological analysis. By means of a x40 stereoscope pottery fabrics were macroscopically described and classified in 32 major ceramic ware groups and further subgroups (plain handmade wares not included). Macroscopic fabric descriptions and ware characterisations were supported by an extensive Neutron Activations Analysis project that was conducted in cooperation with Hans Mommsen (forthcoming). The typological study of the ceramic material of Sindos resulted after detailed contextual analysis and cross-comparison with other contexts in the Aegean and Mediterranean, where pottery shapes and fabrics of the same type as those at Sindos were also in use. Finally, statistical analysis based exclusively on rim sherd count of 4897 fragments from the best stratified settlement contexts [ 28 ] [ 35 ].

Well-dated, non-local pottery facilitated correlation with other regional chronological systems in the Aegean, which was further achieved through analytical studies and cross-checking of local ceramic types. The origin of the local and non-local (mainly Euboean and Attic) pottery types that were used at Sindos has been scientifically defined by means of Neutron Activation Analysis of a representative pottery sample (see above). The non-local pottery used in certain settlement phases comprised a considerable part of the total ceramic assemblage consumed at the site. In particular, 5% of the total pottery in the settlement phase 8 was not local; in phases 7 and 6 the rate was 7% and 9% respectively. The majority of the non-local pottery at Sindos came from Euboea: 92% of the imported wares from phase 7 (169 individuals) came from that island [ 28 ]. The use of such large quantities of non-local pottery can barely support its perception as commodity of particular symbolic or other value that may have remained in use for some considerably longer period of time than it did in its place of origin/production. The assumption of overall short-use is further supported by the fact that broken vessels of non-local origin were never repaired–as otherwise usually happened with similar wares in other non-Greek contexts, where bore holes are common on Greek pots–but were immediately rejected. Finally, most of the non-local pots do not show traces of intense use such as chipping and wearing of the paint. It is thus reasonable to assume that the time from production to final deposition of these pots was not considerably different between the place of origin and place of consumption.

In the lowest 14 C-dated phase 11 at Sindos, for the first time in the stratigraphy, we find pottery sherds of wheel-made vases with concentric semicircles. At Kastanas and Lefkandi, this motive appears for the first time during the Middle Protogeometric period. Nonetheless, phase 11 of Sindos probably does not date that early, since a skyphos fragment with a group of zig-zag lines in the handle zone from this phase has numerous parallels in phase 10 at Kastanas that has been firmly dated to Late Protogeometric [ 28 ] [ 36 ].

The pottery from the immediately following phase 10 of Sindos points to a correlation with the Early Geometric or Subprotogeometric I–II periods in southern and central Greece. In this settlement phase appear at Sindos for the first time–at least in considerable numbers–the Thessalo-macedonian cantharoi of type I. This phase has also yielded the earliest fragments of pendent semicircle skyphoi at Sindos as well as numerous fragments of northern Aegean Transport Amphoras of transitional type. Although production of most of these pottery types began in the Late Protogeometric, and continued into the next period, phase 10 can be dated in the Early Geometric or Subprotogeometric I–II phases, i.e. in the first half of the 9 th century according to the conventional chronology, by means of a sherd from a bowl with offset rim that finds good parallels in a closed burial context of the Subprotogeometric I–II at Lefkandi according to the local ceramic sequence [ 28 ].

The overall picture for the ceramic assemblage of phase 9 leaves no doubt that its wheel- and handmade pottery belongs to a period earlier than Middle Geometric II. Especially two ceramic sherds from closed contexts offer a firm date in Middle Geometric I/Subprotogeometric IIIa. On the one hand, the terminus ante quem is set by a fragment of a pendent semicircle skyphos of type 2, which was not produced any more after the end of the Middle Geometric I/Subprotogeometric period IIIa. The terminus post quem for the date of phase 9, on the other hand, is offered by a sherd of Euboean crater with monochrome conical foot decorated with horizontal bulges. This fragment comes from a crater of type II, which cannot be earlier than Middle Geometric I/Subprotogeometric IIIa.

In settlement phase 8 considerable quantities of imported ceramic wares were now used at Sindos for the first time. The most common non-local wares were pendent semicircle skyphoi of the types 4 and 5 that are usually dated in Middle Geometric II, i.e. first half of the 8 th century according to the conventional chronology. This relative chronology of phase 8 is confirmed by several other imported Euboean and Attic wares, which cannot typologically date before Middle Geometric II or after the beginning of Late Geometric. Buildings and other structures of the two best pottery-dated phases predating the Late Geometric phase 7 were excavated on the upper as well as lower table of the settlement [ 28 ].

With phase 7 the settlement of Sindos reached its largest extent (5 ha), and also experienced some remarkable transformations in material culture, including significant innovations in its pottery technology and consumption [ 35 ]. Phase 7 is securely dated by means of Attic and Euboean pottery to Late Geometric Ia, a chronological sub-period that allegedly occupied a single decade, which would make it by far the shortest settlement phase at Sindos, according to the conventional chronology [ 28 ]. During phase 7 deep Euboean skyphoi decorated with concentric circles, dashes and other linear motives on the high lip as well as panels with meanders or hooks and chevrons ( Fig 9 ) or metopes with birds and quatrefoils in the handle zone–all of which are typical of the Late Geometric I period–appeared for the first time at Sindos. At the same time some very characteristic and well-dated Attic vases of Late Geometric Ia with exact typological parallels in the well-defined seriations of Attic pottery were also imported and used at Sindos ( Fig 10 ).

After the destruction of phase 7 by fire, the lower table was not occupied again until the middle of the 6 th century BC, according to the conventional Aegean chronology. The new settlement of phase 6 was now restricted to the smaller plateau of the higher table. The datable pottery of this phase comes mostly from Euboea and continues the previous tradition of the deep skyphoi with the characteristic motives on the lip and the decoration of the handle zone with metopes and panels with hatched hooks and meanders that disappeared only in Late Geometric II. This settlement phase has been subsequently dated to the sub-period Late Geometric Ib, which was defined in Athens by means of a sequence of burial contexts in combination with typological criteria. The next two habitation phases at Sindos, which both predate the 7 th and early 6 th century hiatus, both belong to the Late Geometric period. Their pottery shows features of the later typological developments in the Euboean ceramic sequence that leave no doubt for an assignment to Late Geometric II [ 28 ].

Implications of Sindos stratigraphy for the Greek relative chronology of the Early Iron Age

The study of the pottery finds at Sindos has strongly enhanced our understanding of the temporal changes in ceramic styles not only in the northern but also in the central Aegean, especially during the Geometric period [ 28 ]. Already for this period, there are eight successive phases at Sindos, two of which–phases 7 and 8 –have been excavated to some large extent. Thanks to the continuous stratigraphy of Sindos, it was possible to elucidate for the first time the typo-chronological development of local ceramic categories such as the Protogeometric and Geometric Transport Amphoras and the K 22-Ware as well as certain categories of Euboean wares, such the pendent semicircle skyphoi, the chevron skyphoi ( Fig 9 ) and other types of Atticising and Euboeaning Geometric pottery.

Another significant outcome of pottery studies at Sindos is that certain ceramic wares, previously identified as hallmarks of the pottery production at microregions in central Greece such as Euboea were apparently also locally produced in Macedonia. What is also important, the Macedonian pottery production does not simply imitate the allegedly innovative pottery styles of these regions, which are usually perceived as ‘centres’ with more complex social and economic organisation. Even the local Macedonian wares were part of a common pottery tradition that was dominant everywhere in the north-western Aegean, from Chalkidike and central Macedonia to eastern Thessaly, Phthiotis, Euboea and northern Cyclades [ 37 ]. We recognise that, for example, locally produced skyphoi with pendent semicircles of the same types were produced and used at the same time in Macedonia and Euboea. In clear contradiction to earlier art historical conceptualisations of ancient pottery production and exchange, the recent typo-chronological analysis of the pendent semicircle skyphoi, based on the new finds from Sindos and other sites in central and western Macedonia, shows that the invention of this type in Euboea should not be taken for granted. We should thus keep distance from views that regard the production of many well-known ceramic types in the Aegean ‘periphery’ as later adaptions to stylistic innovations that originated at certain ‘centres’. The use of essentially identical pottery types of both Euboean and Macedonian origin took place, as it now appears, at the same time at Sindos. This conclusion is significant for the purposes of the present study since it allows to argue also by means of local pottery for the correlation of northern and central Aegean relative chronological systems [ 28 ].

It would be fair to state that the stratigraphy of Sindos has proven as helpful for our comprehension of the temporal development of the many non-local ceramic wares, as the excavations conducted at their assumed place of origin. This is true for certain categories of Euboean Middle and Late Geometric pottery that were widely circulating and used in other regions of the Mediterranean, the typological development of which was a much-disputed topic. The most recent excavations at Eretria and their subsequent publication have added much knowledge for the typological development of these wares, but a detailed pottery sequence is still missing in Euboea itself, since the Eretrian pottery contexts are only broadly datable into two or more chronological periods [ 38 ] [ 39 ]. The fine stratigraphy at Sindos provided more detailed information concerning the typological development of Euboean pottery, especially during Middle and Late Geometric [ 28 ].

There are two main reasons that Euboean and Corinthian pottery of the Geometric period has attracted so much scholarly interest in the past decades: first, these are some of the earliest Aegean wares that were circulated and massively used in the Mediterranean after a long break following the end of the Late Bronze Age. Second, the same wares provide what is perceived through a culture-historical perspective as hard evidence for the Greek colonisation.

Even when viewed from the traditional centre-periphery perspective that has dominated historical interpretations for the last two centuries, Sindos offers detailed data not only for the ‘regional’ Macedonian pottery sequence, but also to comprehend the developments at certain ‘centres’ of the central and southern Aegean. In conclusion, due to its long and continuous stratigraphic sequence and its potential for both long- and short-distance correlation of pottery styles the site of Sindos is one of the few places in the Aegean, where it is possible to test the historical chronology of the Early Iron Age. In the present paper this is now accomplished by a series of radiocarbon dates that were measured on a long stratigraphic sequence of short-lived bone samples.

Revision of the Greek Early Iron Age chronology by means of the new radiocarbon dates from Sindos

The new radiocarbon dates from Sindos have important implications for the Greek Early Iron Age chronology, in particular for the periods older than Late Geometric Ib. The dates for the end of the Late Geometric and the beginning of the Archaic period are less affected. A comparison of the newly achieved 14 C-based absolute chronology from Sindos with the conventional chronology is provided in Fig 11 .

It is noteworthy that the traditional sequence of Protogeometric and Geometric periods is well-confirmed by the stratified 14 C-ages from Sindos. Already the satisfactory coherence of the relative pottery sequence, as established at Sindos in high stratigraphic resolution, speaks for the wider applicability of the new chronology. This, of course, requires further confirmation.

The first major implication of the new chronology relates to our understanding of the Late Geometric I period, which is usually perceived as a transformative phase not only for Greece but also for the Mediterranean through an intensification of contacts between the Aegean and the Levant, and the beginning of Greek ‘colonial’ expansion towards the West. All these events are thought to have taken place within a single generation, from 760 to 735 BC (see analytically above). Eight 14 C determinations from phases 6 and 7 at Sindos dating in Late Geometric Ib and Ia respectively present new solid evidence for a redefinition of this historically significant phase. Hints for a higher chronology of the Late Geometric I period from problematic contexts in central and western Mediterranean such as those of Carthage and others, where random Geometric pottery sherds were found [ 40 ] [ 41 ], are confirmed by the new 14 C-series from the northern Aegean, which show that this period may have been longer than usually thought. At Sindos it has empirically measured time span of ca. 130/140 years. Interestingly, the limit between Late Geometric Ia and Ib is now set at 790 calBC and beginning of Late Geometric I at 870 calBC. Settlement phase 7 of Sindos, which dates to the allegedly only short period of Late Geometric Ia, is the best sampled (N = 6 14 C-ages) settlement phase of the entire sequence. In addition, since the 14 C-ages from phase 7 reach well into the steep section of the calibration curve, Late Geometric Ia is also the most precisely dated period at Sindos. In consequence, Late Geometric Ia should not be taken any more as the shortest chronological phase of the Greek Early Iron Age as originally perceived by Coldstream. It covers a time-span much longer than that of other Geometric periods ( Fig 11 ), just as suggested based on the many discernible cultural changes and innovations that took place during this period, all around the Mediterranean.

Three 14 C-determinations from phase 8 raise the beginning of Middle Geometric II from 800 histBC to 930 calBC, a result which agrees well with the recently published radiocarbon dates for seeds from a secure context at Utica in Tunisia, which contained plentiful amounts of Middle Geometric II pottery [ 42 ].

Three further 14 C-ages from settlement phase 9 place Middle Geometric I well into the 10th century, while five 14 C determinations from phase 10 may raise the Early Geometric period–again by around 100 to 150 years–into the second half of the 11th century BC.

Finally, two radiocarbon dates from phase 11 at Sindos that probably dates to Late Protogeometric seem to place this phase of the relative Greek chronology into the first half of the 11th century BC.

Due to missing scientific evidence we may only assume that the underlying Early and Middle Protogeometric would date somewhere before the end of the 12th and beginning of the 11th century BC. To this point it is important to remember the conjectural character of the tripartite definition of the Protogeometric period. Strongly in need of clarification, in relative terms, is the definition of its Middle phase, which is exclusively based on some few mortuary contexts in combination with some not well-defined typological sequences in central and southern Greece. It is mainly for these reasons that the Middle Protogeometric is an extremely elusive phase, especially within settlement contexts.

Sindos is the first Aegean site for which a continuous sequence of 14 C-ages on short-lived samples (animal bones) from the Early Iron Age is now available. Its main amenity is to support critical evaluation of the orthodox historical chronology for the Protogeometric and Geometric periods in north, central and southern Greece. Classical archaeology has long relished a quite unique privilege throughout the circum-Mediterranean chronological systems, in that the underlying absolute dates are based on comprehensive faith in the validity of the antique historiography. The proposed revision of the Greek Early Iron Age (absolute) chronology is in accordance with previous analyses and studies in the northern Aegean as well as in the eastern and western Mediterranean that support a higher chronology [ 4 ] [ 9 ] [ 40 ] [ 41 ] [ 42 ] [ 43 ], if only within given error limits.

Interestingly, the ascertained discrepancies appear to have their largest (joint) cause in the very short time-span (~10 yrs) that is traditionally assigned to Late Geometric Ia. Once introduced–apparently within ±10 yrs of the beginning of the Late Geometric–from that point in time backwards the dating offset remains effectively constant (in the order of 50–80 yrs) for several hundreds of years. At Sindos this ‘down-core’ propagation (wrongly younger) of a nominally constant error (cf. nearly parallel diagonal lines in Fig 11 ) is observable for all phases 7–11, with the notable exception of phase 6 (Late Geometric Ib). A memory-effect for a propagated dating error with this (actually quite small) magnitude would readily explain many of the observed discrepancies between the different chronologies, which are typically of given magnitude, and in particular the proposed updating of the Early Protogeometric at Assiros [ 4 ]. Unfortunately, it is not the initial occurrence of the dating error itself (in Late Geometric Ib), nor its first propagation steps (through the Middle Geometric), but rather more its down-core arrival in the Protogeometric that is difficult to judge. Namely, as can be taken from Fig 11 , for ages older than ca.1000 calBC the GaussWM-derived dating errors from Sindos have values of ±50 yrs (95%) and higher. For all phases of the Protogeometric, this imprecision effectively hampers further meaningful comparisons.

Conclusions

Implications of the revision of greek chronology on aegean and mediterranean archaeology.

It is especially for the younger sections of the Aegean Early Iron Age, in particular for the Late Protogeometric and Geometric periods, that the new data from Sindos may have an impact in our general perception of the cultural and social transformations that took place in the Mediterranean. After a long period of time interregional contacts between Greece and the eastern Mediterranean began again from the Late Protogeometric onwards, while exchanges between the Aegean and Italy were restored in the following Geometric periods. From an archaeological perspective, these contacts are not only recognisable but also best-dated by means of pottery synchronisms. For example, circulation and consumption of drinking cups of the Middle Geometric and Late Geometric I periods overseas are in certain quarters perceived as indicators of Greek and Phoenician ‘pre- or early colonial’ activity. During those periods the Greeks, and probably also other people, are usually thought to have adopted the alphabet from the Phoenicians, appropriated new cultural and social habits such as the symposion, and prepared the ground for one of the most influential events in Mediterranean history, the ‘apoikismos’. According to the conventional chronology all this is thought to have taken place within a period of two generations, from 800 to 735 BC. Particularly significant in this respect is the allegedly short Late Geometric Ia phase, but which probably contains the bulk of the so-called ‘pre-colonial’ pottery in western Mediterranean. The proposed changes in the absolute Greek and consequently Mediterranean chronology may thus change our understanding of the timing and duration of (short) historical events, or (long) cultural processes that took place during the Early Iron Age. One of the rising questions is, for example, whether the transfer of writing really did take place within the time-span of only one generation, as is often assumed, and whether its adoption really did occur at some time in the 8th century calBC, or not already in the second half of the 9 th century calBC. Furthermore, the archaeologically visible restoration of contacts between the Aegean and the western Mediterranean, following the end of the Late Bronze Age, may not date to the first half of the 8th century calBC, but this occurred instead–based on the new evidence from Sindos–much earlier.

Any attempt to revise a well-established and widely respected–despite its deficiencies–chronological system is a major challenge. Dating revisions even on the seemingly small (multi-decadal) scale proposed here will naturally be perceived as inconvenient, in many respects, but herein especially due to their implications for the chronological systems and historical narratives of the Early Iron Age that are accepted as authoritative on a supra-regional scale. Instead, we put forward for the first time a series of radiocarbon dates for the Protogeometric and Geometric periods in the Aegean. The results contradict many of the interpretations that were based on, in our view, some largely ambiguous historiographic and archaeological dating methods. What is certainly needed are many further series of 14 C-ages that derive from secure and well-published contexts in the Aegean and other regions, where Greek pottery was used, at best from long tell-stratigraphies and in combination with large-scale statistical pottery dating, based e.g. on Correspondence Analysis [ 34 ].

Acknowledgments

Problems of the Greek and Mediterranean Late Bronze and Early Iron Age were discussed with many colleagues. We are particularly grateful to José Luis Lopez Castro, Alfredo Mederos Martín, Gunnar Lehmann and Francisco J. Nuñez. Special thanks are also to Alfred Galik, who carefully examined the animal bones from Sindos. The comments and suggestions made by the anonymous reviewers of this paper were critical, as well as substantial and helpful in many aspects, and also deserve our particular accreditation. The permission for sampling and 14 C-analysis was kindly issued by the Greek authorities.

Funding Statement

The dating project was funded within the budgets of the stand-alone FWF projects P 26150 and P 30475 that were implemented by Stefanos Gimatzidis ( https://www.fwf.ac.at/de/ ). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability

Using Graphic Organizers for Writing Essays, Summaries and Research

Ask any student – essay writing is one of the most despised tasks of their educational career. Perhaps there is so much displeasure associated with the task because it’s perceived as too linear – there isn’t enough visual and creative appeal. But if you use graphic organizer for writing essays then you can make writing enjoyable – or at least less terrible.

Not only enjoyable but graphic organizers (or diagrams) can make the writing process a snap. They’ll help you think outside the box, draw conclusions you wouldn’t normally observe, and make the entire process faster and more efficient.

Why Use Graphic Organizers for Writing

The phrase “graphic organizer” is just a fancy way of saying “diagram” or “visual aid.” Basically, they are a visual representation of the information you’ve acquired in the research process. There are quite a few reasons why you should use them when writing essays or summaries.

• Helps you visualize your research and how elements connect with each other
• Enhance your essays, summaries and research papers with visual elements
• Track correlations between your thoughts, observations, facts or general ideas

When it comes to essay writing, the most common graphic organizers are webs, mind maps, and concept maps .

Using Webs for Brainstorming

Webbing is a great way to see how various topics are interrelated. This graphic organizer is particularly useful during the brainstorming step of the writing process.

A web can sometimes get a bit messy. Usually, there are lots of arrows to connect overlapping ideas. However, even with lines crisscrossing every which way, it is still a great way to visualize your thoughts. If you’re using an online diagramming software like Creately you can overcome some of this because we automatically arrange the object for you.

Once you’ve created a map to document all your ideas and establish connections, you can easily transition to other forms of diagramming to better organize the information.

For example if you’re writing a research paper about the food web of the Australian bushes you can start creating a food web diagram similar to the one below. This way you can easily visualize the web while writing the paper. This is a simple example but graphic organizers become even more important when the subject gets complex.

Although simple this example shows the importance of using graphic organizers for writing summaries. A comprehensive diagram pretty much does the summation for you.

Using Mind Maps as Graphic Organizers

Mind maps are a great way to depict a hierarchy. What is hierarchical organization ? The concept is simple: a singular topic dominates with each subsequent idea decreasing in importance.

Usually, the mind map starts with the thesis (or main idea) at the center.  From there, you can branch out with your supporting evidence.

Use this process to replace your traditional note taking technique – note cards, outlines, whatever. You’ll quickly realize a mind map is a great way to formulate the structure of your essay. The thing to note here is that the nature of the mind maps force you think about sub topics and how to organize your ideas. And once the ideas are organized writing the essay become very easy.

Above is a mind map of a research proposal. Click on it to see the full image or you can see the fully editable template via this link . As you can see in this mind map the difference areas of the research proposal is highlighted. Similarly when your writing the research paper you can use a mind map to break it down to sub topics. We have more mind map templates for you to get started.

Concept Maps

A concept map will help you visualize the connection between ideas. You can easily see cause and effect – how one concept leads to another. Often times, concept mapping includes the use of short words or phrases to depict the budding relationship between these concepts.

If you look closely you can see that its very similar to a mind map. But a concept maps gives more of a free reign compares to the rigid topic structure of a mind map. I’d say it’s the perfect graphic organizer for writing research papers where you have the license to explore.

By creating a concept map , you can also see how a broad subject can be narrowed down into specific ideas.  This is a great way to counter writers block.  Often, we look at the big picture and fail to see the specifics that lead to it.  Identifying contributing factors and supporting evidence is difficult. But with a concept map, you can easily see how the smaller parts add up to the whole.

Why Bother With Graphic Organizers?

If you already detest the writing process, adding another step might seem insane. However, there really are several advantages of using them.  If you haven’t already accepted the benefits of each individual diagram style, here are some more perks of graphic organizers in general:

• Quality essays are based on detail. No one is going to accept your opinions and reasoning just because you say so. You’ll need proof. And organizing that proof will require attention to detail. Graphic organizers can help you see that detail and how it contributes to the overall concept.
• Graphic organizers are flexible. You don’t need one of those giant pink erasers. You don’t need to restructure your outline. All you have to do is draw a few arrows and bam – the relationship has totally changed.
• No matter what you are writing about, a graphic organizer can help. They can be used to structure an essay on the Great Wall, theoretical physics, or Spanish speaking countries.
• If you write an outline, can you easily see how point A influences point X? Probably not. But if little thought bubble A is sitting out there all by itself, you can visualize the way it ties into point R, T and X.
• Some of us find it difficult to put our opinions, thoughts, and ideas into writing. However, communicating our feelings with little doodles and sketches is far less threatening.
• As a writer, our brain often feels like a 2-year-old’s toy box – a big jumbled mess. Taking that mess and putting it onto paper with some semblance of organization is challenging. Rather than trying to take your thoughts from total chaos to a perfectly structured list, just try to get them out of your brain and onto paper in the form of a diagram.
• A graphic organizer helps you establish validity and relevance. You can easily nix the ideas that don’t support or enhance your thesis.

The next time you are faced with a writing project, take a few minutes to explore the efficiency of graphic organizers. You can find a wealth of templates here.

Have you ever used a graphic organizer to structure an essay? How did it go? Do you have a diagram suggestion for the writing process that wasn’t mentioned here? Let us know!

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