history of earth essay

Formation of Earth

Our planet began as part of a cloud of dust and gas. It has evolved into our home, which has an abundance of rocky landscapes, an atmosphere that supports life, and oceans filled with mysteries.

Chemistry, Earth Science, Astronomy, Geology

Manicouagan Crater

Asteroids were not only important in Earth's early formation, but have continued to shape our planet. A five-kilometer (three-mile) diameter asteroid is theorized to have formed the Manicouagan Crater about 215.5 million years ago.

We live on Earth’s hard, rocky surface, breathe the air that surrounds the planet , drink the water that falls from the sky, and eat the food that grows in the soil. But Earth did not always exist within this expansive universe, and it was not always a hospitable haven for life. Billions of years ago, Earth, along with the rest of our solar system, was entirely unrecognizable, existing only as an enormous cloud of dust and gas. Eventually, a mysterious occurrence—one that even the world’s foremost scientists have yet been unable to determine—created a disturbance in that dust cloud, setting forth a string of events that would lead to the formation of life as we know it. One common belief among scientists is that a distant star collapsed, creating a supernova explosion, which disrupted the dust cloud and caused it to pull together. This formed a spinning disc of gas and dust, known as a solar nebula . The faster the cloud spun, the more the dust and gas became concentrated at the center, further fueling the speed of the nebula . Over time, the gravity at the center of the cloud became so intense that hydrogen atoms began to move more rapidly and violently. The hydrogen protons began fusing, forming helium and releasing massive amounts of energy. This led to the formation of the star that is the center point of our solar system—the sun—roughly 4.6 billion years ago. Planet Formation The formation of the sun consumed more than 99 percent of the matter in the nebula . The remaining material began to coalesce into various masses. The cloud was still spinning, and clumps of matter continued to collide with others. Eventually, some of those clusters of matter grew large enough to maintain their own gravitational pull, which shaped them into the planets and dwarf planets that make up our solar system today. Earth is one of the four inner, terrestrial planets in our solar system. Just like the other inner planets —Mercury, Venus, and Mars—it is relatively small and rocky. Early in the history of the solar system, rocky material was the only substance that could exist so close to the Sun and withstand its heat. In Earth's Beginning At its beginning, Earth was unrecognizable from its modern form. At first, it was extremely hot, to the point that the planet likely consisted almost entirely of molten magma . Over the course of a few hundred million years, the planet began to cool and oceans of liquid water formed. Heavy elements began sinking past the oceans and magma toward the center of the planet . As this occurred, Earth became differentiated into layers, with the outermost layer being a solid covering of relatively lighter material while the denser, molten material sunk to the center. Scientists believe that Earth, like the other inner planets , came to its current state in three different stages. The first stage, described above, is known as accretion, or the formation of a planet from the existing particles within the solar system as they collided with each other to form larger and larger bodies. Scientists believe the next stage involved the collision of a proto planet with a very young planet Earth. This is thought to have occurred more than 4.5 billion years ago and may have resulted in the formation of Earth’s moon. The final stage of development saw the bombardment of the planet with asteroids . Earth’s early atmosphere was most likely composed of hydrogen and helium . As the planet changed, and the crust began to form, volcanic eruptions occurred frequently. These volcanoes pumped water vapor, ammonia, and carbon dioxide into the atmosphere around Earth. Slowly, the oceans began to take shape, and eventually, primitive life evolved in those oceans. Contributions from Asteroids Other events were occurring on our young planet at this time as well. It is believed that during the early formation of Earth, asteroids were continuously bombarding the planet , and could have been carrying with them an important source of water. Scientists believe the asteroids that slammed into Earth, the moon, and other inner planets contained a significant amount of water in their minerals, needed for the creation of life. It seems the asteroids , when they hit the surface of Earth at a great speed, shattered, leaving behind fragments of rock. Some suggest that nearly 30 percent of the water contained initially in the asteroids would have remained in the fragmented sections of rock on Earth, even after impact. A few hundred million years after this process—around 2.2 billion to 2.7 billion years ago—photosynthesizing bacteria evolved . They released oxygen into the atmosphere via photosynthesis and, in a few hundred million years, were able to change the composition of the atmosphere into what we have today. Our modern atmosphere is comprised of 78 percent nitrogen and 21 percent oxygen, among other gases, which enables it to support the many lives residing within it.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

October 19, 2023

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

Covering a story? Visit our page for journalists or call (773) 702-8360.

New Certificate Program

Top Stories

• Inside the Lab: A first-hand look at University of Chicago research
• Scav reflections: “for the love of the pursuit and the joy in the attempt”

W. Ralph Johnson, pre-eminent UChicago critic of Latin poetry, 1933‒2024

The origin of life on earth, explained.

The origin of life on Earth stands as one of the great mysteries of science. Various answers have been proposed, all of which remain unverified. To find out if we are alone in the galaxy, we will need to better understand what geochemical conditions nurtured the first life forms. What water, chemistry and temperature cycles fostered the chemical reactions that allowed life to emerge on our planet? Because life arose in the largely unknown surface conditions of Earth’s early history, answering these and other questions remains a challenge.

Several seminal experiments in this topic have been conducted at the University of Chicago, including the Miller-Urey experiment that suggested how the building blocks of life could form in a primordial soup.

Jump to a section:

• When did life on Earth begin?

Where did life on Earth begin?

What are the ingredients of life on earth, what are the major scientific theories for how life emerged, what is chirality and why is it biologically important, what research are uchicago scientists currently conducting on the origins of life, when did life on earth begin .

Earth is about 4.5 billion years old. Scientists think that by 4.3 billion years ago, Earth may have developed conditions suitable to support life. The oldest known fossils, however, are only 3.7 billion years old. During that 600 million-year window, life may have emerged repeatedly, only to be snuffed out by catastrophic collisions with asteroids and comets.

The details of those early events are not well preserved in Earth’s oldest rocks. Some hints come from the oldest zircons, highly durable minerals that formed in magma. Scientists have found traces of a form of carbon—an important element in living organisms— in one such 4.1 billion-year-old zircon . However, it does not provide enough evidence to prove life’s existence at that early date.

Two possibilities are in volcanically active hydrothermal environments on land and at sea.

Some microorganisms thrive in the scalding, highly acidic hot springs environments like those found today in Iceland, Norway and Yellowstone National Park. The same goes for deep-sea hydrothermal vents. These chimney-like vents form where seawater comes into contact with magma on the ocean floor, resulting in streams of superheated plumes. The microorganisms that live near such plumes have led some scientists to suggest them as the birthplaces of Earth’s first life forms.

Organic molecules may also have formed in certain types of clay minerals that could have offered favorable conditions for protection and preservation. This could have happened on Earth during its early history, or on comets and asteroids that later brought them to Earth in collisions. This would suggest that the same process could have seeded life on planets elsewhere in the universe.

The recipe consists of a steady energy source, organic compounds and water.

Sunlight provides the energy source at the surface, which drives photosynthesis. On the ocean floor, geothermal energy supplies the chemical nutrients that organisms need to live.

Also crucial are the elements important to life . For us, these are carbon, hydrogen, oxygen, nitrogen, and phosphorus. But there are several scientific mysteries about how these elements wound up together on Earth. For example, scientists would not expect a planet that formed so close to the sun to naturally incorporate carbon and nitrogen. These elements become solid only under very cold temperatures, such as exist in the outer solar system, not nearer to the sun where Earth is. Also, carbon, like gold, is rare at the Earth’s surface. That’s because carbon chemically bonds more often with iron than rock. Gold also bonds more often with metal, so most of it ends up in the Earth’s core. So, how did the small amounts found at the surface get there? Could a similar process also have unfolded on other planets?

The last ingredient is water. Water now covers about 70% of Earth’s surface, but how much sat on the surface 4 billion years ago? Like carbon and nitrogen, water is much more likely to become a part of solid objects that formed at a greater distance from the sun. To explain its presence on Earth, one theory proposes that a class of meteorites called carbonaceous chondrites formed far enough from the sun to have served as a water-delivery system.

There are several theories for how life came to be on Earth. These include:

Life emerged from a primordial soup

As a University of Chicago graduate student in 1952, Stanley Miller performed a famous experiment with Harold Urey, a Nobel laureate in chemistry. Their results explored the idea that life formed in a primordial soup.

Miller and Urey injected ammonia, methane and water vapor into an enclosed glass container to simulate what were then believed to be the conditions of Earth’s early atmosphere. Then they passed electrical sparks through the container to simulate lightning. Amino acids, the building blocks of proteins, soon formed. Miller and Urey realized that this process could have paved the way for the molecules needed to produce life.

Scientists now believe that Earth’s early atmosphere had a different chemical makeup from Miller and Urey’s recipe. Even so, the experiment gave rise to a new scientific field called prebiotic or abiotic chemistry, the chemistry that preceded the origin of life. This is the opposite of biogenesis, the idea that only a living organism can beget another living organism.

Seeded by comets or meteors

Some scientists think that some of the molecules important to life may be produced outside the Earth. Instead, they suggest that these ingredients came from meteorites or comets.

“A colleague once told me, ‘It’s a lot easier to build a house out of Legos when they’re falling from the sky,’” said Fred Ciesla, a geophysical sciences professor at UChicago. Ciesla and that colleague, Scott Sandford of the NASA Ames Research Center, published research showing that complex organic compounds were readily produced under conditions that likely prevailed in the early solar system when many meteorites formed.

Meteorites then might have served as the cosmic Mayflowers that transported molecular seeds to Earth. In 1969, the Murchison meteorite that fell in Australia contained dozens of different amino acids—the building blocks of life.

Comets may also have offered a ride to Earth-bound hitchhiking molecules, according to experimental results published in 2001 by a team of researchers from Argonne National Laboratory, the University of California Berkeley, and Lawrence Berkeley National Laboratory. By showing that amino acids could survive a fiery comet collision with Earth, the team bolstered the idea that life’s raw materials came from space.

In 2019, a team of researchers in France and Italy reported finding extraterrestrial organic material preserved in the 3.3 billion-year-old sediments of Barberton, South Africa. The team suggested micrometeorites as the material’s likely source. Further such evidence came in 2022 from samples of asteroid Ryugu returned to Earth by Japan’s Hayabusa2 mission. The count of amino acids found in the Ryugu samples now exceeds 20 different types .

In 1953, UChicago researchers published a landmark paper in the Journal of Biological Chemistry that marked the discovery of the pro-chirality concept , which pervades modern chemistry and biology. The paper described an experiment showing that the chirality of molecules—or “handedness,” much the way the right and left hands differ from one another—drives all life processes. Without chirality, large biological molecules such as proteins would be unable to form structures that could be reproduced.

Today, research on the origin of life at UChicago is expanding. As scientists have been able to find more and more exoplanets—that is, planets around stars elsewhere in the galaxy—the question of what the essential ingredients for life are and how to look for signs of them has heated up.

Nobel laureate Jack Szostak joined the UChicago faculty as University Professor in Chemistry in 2022 and will lead the University’s new interdisciplinary Origins of Life Initiative to coordinate research efforts into the origin of life on Earth. Scientists from several departments of the Physical Sciences Division are joining the initiative, including specialists in chemistry, astronomy, geology and geophysics.

“Right now we are getting truly unprecedented amounts of data coming in: Missions like Hayabusa and OSIRIS-REx are bringing us pieces of asteroids, which helps us understand the conditions that form planets, and NASA’s new JWST telescope is taking astounding data on the solar system and the planets around us ,” said Prof. Ciesla. “I think we’re going to make huge progress on this question.”

Last updated Sept. 19, 2022.

Faculty Experts

Clara Blättler

Fred Ciesla

Jack Szostak

Recommended Stories

Earth could have supported crust, life earlier than thought

Earth’s building blocks formed during the solar system’s first…

Additional Resources

The Origins of Life Speaker Series

Recommended Podcasts

Big Brains podcast: Unraveling the mystery of life’s origins on Earth

Discovering the Missing Link with Neil Shubin (Ep. 1)

More Explainers

Improv, Explained

Cosmic rays, explained

Related Topics

Latest news, ‘inside the lab’ series provides a unique look at uchicago research.

Mavis Staples, legendary singer and activist, returns to UChicago to inspire next generation

Geophysical Sciences

Scientists find evidence that meltwater is fracturing ice shelves in Antarctica

Pritzker School of Molecular Engineering

UChicago scientists use machine learning to turn cell snapshots dynamic

Where do breakthrough discoveries and ideas come from?

Explore The Day Tomorrow Began

Pulitzer Prize

Trina Reynolds-Tyler, MPP'20, wins Pulitzer Prize in Local Reporting

Around uchicago, uchicago to offer new postbaccalaureate premedical certificate program.

Carnegie Fellow

UChicago political scientist Molly Offer-Westort named Carnegie Fellow

National Academy of Sciences

Five UChicago faculty elected to National Academy of Sciences in 2024

Laing Award

UChicago Press awards top honor to Margareta Ingrid Christian for ‘Objects in A…

Winners of the 2024 UChicago Science as Art competition announced

Six UChicago scholars elected to American Academy of Arts and Sciences in 2024

Biological Sciences Division

“You have to be open minded, planning to reinvent yourself every five to seven years.”

UChicago paleontologist Paul Sereno’s fossil lab moves to Washington Park

Historical Geology

A free online textbook for Historical Geology courses

A Brief History of Earth

After reading this chapter, students should be able to:

• Describe the origins the of the Universe in the context of Big Bang theory
• Describe the origins of our solar system in the context of nebular theory
• Identify major tectonic and biologic events that occurred in various geologic eons

Based on An Introduction to Geology, Chapter 8: Earth History

Entire courses and careers have been based on the wide-ranging topics covering Earth’s history. Throughout the long history of Earth, change has been the norm. Looking back in time, an untrained eye would see many unfamiliar life forms and terrains. The main topics studied in Earth history are paleogeography, paleontology, and paleoecology and paleoclimatology —respectively, past landscapes, past organisms, past ecosystems, and past environments. This chapter will cover (briefly) the origin of the universe and the 4.6 billion year history of Earth. It will act as a guide, linking out to other chapters, case studies, and sections in this book.

Origin of the Universe

The universe appears to have an infinite number of galaxies and solar systems and our solar system occupies a small section of this vast entirety. The origins of the universe and solar system set the context for conceptualizing the Earth’s origin and early history.

Big-Bang Theory

The big-bang theory proposes the universe was formed from an infinitely dense and hot core of material. The bang in the title suggests there was an explosive, outward expansion of all matter and space that created atoms. Spectroscopy confirms that hydrogen makes up about 74% of all matter in the universe. Since its creation, the universe has been expanding for 13.8 billion years and recent observations suggest the rate of this expansion is increasing . 

Spectroscopy

Cosmic Microwave Background Radiation

Stellar Evolution

Birth of a star.

Death of a Star

The death of a star can range from spectacular to other-worldly (see figure). Stars like the Sun form a planetary nebula, which comes from the collapse of the star’s outer layers in an event like the implosion of a building. In the tug-of-war between gravity’s inward pull and fusion’s outward push, gravity instantly takes over when fusion ends, with the outer gasses puffing away to form a nebula. More massive stars do this as well but with a more energetic collapse, which starts another type of energy release mixed with element creation known as a supernova. In a supernova , the collapse of the core suddenly halts, creating a massive outward-propagating shock wave. A supernova is the most energetic explosion in the universe short of the big bang. The energy release is so significant the ensuing fusion can make every element up through uranium .

The death of the star can result in the creation of white dwarfs, neutron stars, or black holes. Following their deaths, stars like the Sun turn into white dwarfs .

White dwarfs are hot star embers, formed by packing most of a dying star’s mass into a small and dense object about the size of Earth. Larger stars may explode in a supernova that packs their mass even tighter to become neutron stars. Neutron stars are so dense that protons combine with electrons to form neutrons. The largest stars collapse their mass even further, becoming objects so dense that light cannot escape their gravitational grasp. These are the infamous black holes and the details of the physics of what occurs in them are still up for debate.

Origin of the Solar System: The Nebular Hypothesis

Planet Arrangement and Segregation

Pluto and planet definition

Geoscientists use the geological time scale to assign relative age names to events and rocks, separating major events in Earth’s history based on significant changes as recorded in rocks and fossils. This section summarizes the most notable events of each major time interval. For a breakdown on how these time intervals are chosen and organized, see chapter 7 .

The Hadean Eon, named after the Greek god and ruler of the underworld Hades, is the oldest eon and dates from 4.5–4.0 billion years ago .  

Origin of Earth’s Crust

Origin of the Moon

Computer simulation of the evolution of the Moon (2 minutes).

Origin of Earth’s Water

Archean Eon

Late Heavy Bombardment

Objects were chaotically flying around at the start of the solar system, building the planets and moons. There is evidence that after the planets formed, about 4.1–3.8 billion years ago, a second large spike of asteroid and comet impacted the Earth and Moon in an event called late heavy bombardment . Meteorites and comets in stable or semi-stable orbits became unstable and started impacting objects throughout the solar system. In addition, this event is called the lunar cataclysm because most of the Moons craters are from this event. During late heavy bombardment, the Earth, Moon, and all planets in the solar system were pummeled by material from the asteroid and Kuiper belts. Evidence of this bombardment was found within samples collected from the Moon.

Origin of the Continents

The first solid evidence of modern plate tectonics is found at the end of the Archean, indicating at least some continental lithosphere must have been in place. This evidence does not necessarily mark the starting point of plate tectonics; remnants of earlier tectonic activity could have been erased by the rock cycle .

The stable interiors of the current continents are called cratons and were mostly formed in the Archean Eon. A craton has two main parts: the shield , which is crystalline basement rock near the surface, and the platform made of sedimentary rocks covering the shield. Most cratons have remained relatively unchanged with most tectonic activity having occurred around cratons instead of within them. Whether they were created by plate tectonics or another process, Archean continents gave rise to the Proterozoic continents that now dominate our planet.

First Life on Earth

Although the origin of life on Earth is unknown, hypotheses include a chemical origin in the early atmosphere and ocean, deep-sea hydrothermal vents, and delivery to Earth by comets or other objects. One hypothesis is that life arose from the chemical environment of the Earth’s early atmosphere and oceans, which was very different than today. The oxygen-free atmosphere produced a reducing environment with abundant methane, carbon dioxide, sulfur, and nitrogen compounds. This is what the atmosphere is like on other bodies in the solar system. In the famous Miller-Urey experiment, researchers simulated early Earth’s atmosphere and lightning within a sealed vessel. After igniting sparks within the vessel, they discovered the formation of amino acids, the fundamental building blocks of proteins.  In 1977, when scientists discovered an isolated ecosystem around hydrothermal vents on a deep-sea mid-ocean ridge (see Chapter 4 ), it opened the door for another explanation of the origin of life. The hydrothermal vents have a unique ecosystem of critters with chemosynthesis as the foundation of the food chain instead of photosynthesis. The ecosystem is deriving its energy from hot chemical-rich waters pouring out of underground towers. This suggests that life could have started on the deep ocean floor and derived energy from the heat from the Earth’s interior via chemosynthesis. Scientists have since expanded the search for life to more unconventional places, like Jupiter’s icy moon Europa.

Animation of the original Miller-Urey 1959 experiment that simulated the early atmosphere and created amino acids from simple elements and compounds.

Another possibility is that life or its building blocks came to Earth from space, carried aboard comets or other objects. Amino acids, for example, have been found within comets and meteorites. This intriguing possibility also implies a high likelihood of life existing elsewhere in the cosmos.

Proterozoic Eon

An oxygenated world also changed the chemistry of the planet in significant ways. For example, iron remained in solution in the non-oxygenated environment of the earlier Archean Eon. In chemistry, this is known as a reducing environment. Once the environment was oxygenated, iron combined with free oxygen to form solid precipitates of iron oxide, such as the mineral hematite or magnetite. These precipitates accumulated into large mineral deposits with red chert known as banded-iron formations, which are dated at about 2 billion years .

The disagreements over these complex reconstructions is exemplified by geologists proposing at least six different models for the breakup of Rodinia to create Australia , Antarctica , parts of China , the Tarim craton north of the Himalaya , Siberia , or the Kalahari craton of eastern Africa . This breakup created lots of shallow-water, biologically favorable environments that fostered the evolutionary breakthroughs marking the start of the next eon, the Phanerozoic.

Life Evolves

Another important event in Earth’s biological history occurred about 1.2 billion years ago when eukaryotes invented sexual reproduction. Sharing genetic material from two reproducing individuals, male and female, greatly increased genetic variability in their offspring. This genetic mixing accelerated evolutionary change, contributing to more complexity among individual organisms and within ecosystems (see Chapter 7 ).

Proterozoic land surfaces were barren of plants and animals and geologic processes actively shaped the environment differently because land surfaces were not protected by leafy and woody vegetation. For example, rain and rivers would have caused erosion at much higher rates on land surfaces devoid of plants. This resulted in thick accumulations of pure quartz sandstone from the Proterozoic Eon such as the extensive quartzite formations in the core of the Uinta Mountains in Utah.

Phanerozoic Eon: Paleozoic Era

Life in the early Paleozoic Era was dominated by marine organisms but by the middle of the era plants and animals evolved to live and reproduce on land . Fish evolved jaws and fins evolved into jointed limbs. The development of lungs allowed animals to emerge from the sea and become the first air-breathing tetrapods (four-legged animals) such as amphibians. From amphibians evolved reptiles with the amniotic egg. From reptiles evolved an early ancestor to birds and mammals  and their scales became feathers and fur. Near the end of the Paleozoic Era, the Carboniferous Period had some of the most extensive forests in Earth’s history. Their fossilized remains became the coal that powered the industrial revolution

Paleozoic Tectonics and Paleogeography

During the Paleozoic Era, sea-levels rose and fell four times. With each sea-level rise, the majority of North America was covered by a shallow tropical ocean. Evidence of these submersions are the abundant marine sedimentary rocks such as limestone with fossils corals and ooids. Extensive sea-level falls are documented by widespread unconformities. Today, the midcontinent has extensive marine sedimentary rocks from the Paleozoic and western North America has thick layers of marine limestone on block faulted mountain ranges such as Mt. Timpanogos near Provo, Utah . 

Animation of plate movement the last 3.3 billion years. Pangea occurs at the 4:40 mark.

While the east coast of North America was tectonically active during the Paleozoic Era, the west coast remained mostly inactive as a passive margin during the early Paleozoic. The western edge of North American continent was near the present-day Nevada-Utah border and was an expansive shallow continental shelf near the paleoequator. However, by the Devonian Period, the Antler orogeny started on the west coast and lasted until the Pennsylvanian Period. The Antler orogeny was a volcanic island arc that was accreted onto western North America with the subduction direction away from North America. This created a mountain range on the west coast of North American called the Antler highlands and was the first part of building the land in the west that would eventually make most of California, Oregon, and Washington states. By the late Paleozoic, the Sonoma orogeny began on the west coast and was another collision of an island arc. The Sonoma orogeny marks the change in subduction direction to be toward North America with a volcanic arc along the entire west coast of North America by late Paleozoic to early Mesozoic Eras .

By the end of the Paleozoic Era, the east coast of North America had a very high mountain range due to continental collision and the creation of Pangea. The west coast of North America had smaller and isolated volcanic highlands associated with island arc accretion. During the Mesozoic Era, the size of the mountains on either side of North America would flip, with the west coast being a more tectonically active plate boundary and the east coast changing into a passive margin after the breakup of Pangea.

Paleozoic Evolution

According to evidence from glacial deposits, a small ice age caused sea-levels to drop and led to a major mass extinction by the end of the Ordovician. This is the earliest of five mass extinction events documented in the fossil record. During this mass extinction, an unusually large number of species abruptly disappear in the fossil record (see video). 

4-minute video describing mass extinctions.

 Land plants had also evolved into the first trees and forests . Toward the end of the Devonian, another mass extinction event occurred. This extinction, while severe, is the least temporally defined, with wide variations in the timing of the event or events. Reef building organisms were the hardest hit, leading to dramatic changes in marine ecosystems .

Permian Mass Extinction

Phanerozoic Eon: Mesozoic Era

8.7.1 Mesozoic Tectonics and Paleogeography

This age pattern shows how the Atlantic Ocean opened as the young Mid-Atlantic Ridge began to create the seafloor. This means the Atlantic ocean started opening and was first formed here. The southern Atlantic opened next, with South America separating from central and southern Africa. Last (happening after the Mesozoic ended) was the northernmost Atlantic, with Greenland and Scandinavia parting ways.  The breaking points of each rifted plate margin eventually turned into the passive plate boundaries of the east coast of the Americas today.

Video of Pangea breaking apart and plates moving to their present locations. By Tanya Atwater.

Tectonics had an influence in one more important geographic feature in North America: the Cretaceous Western Interior Foreland Basin, which flooded during high sea levels forming the Cretaceous Interior Seaway . Subduction from the west was the Farallon Plate, an oceanic plate connected to the Pacific Plate (seen today as remnants such as the Juan de Fuca Plate, off the coast of the Pacific Northwest). Subduction was shallow at this time because a very young, hot and less dense portion of the Farallon plate was subducted. This shallow subduction caused a downwarping in the central part of North America . High sea levels due to shallow subduction, and increasing rates of seafloor spreading and subduction, high temperatures, and melted ice also contributed to the high sea levels . These factors allowed a shallow epicontinental seaway that extended from the Gulf of Mexico to the Arctic Ocean to divide North America into two separate land masses , Laramidia to the west and Appalachia to the east, for 25 million years . Many of the coal deposits in Utah and Wyoming formed from swamps along the shores of this seaway . By the end of the Cretaceous, cooling temperatures caused the seaway to regress .

8.7.2 Mesozoic Evolution

K-T Extinction

Similar to the end of the Paleozoic era, the Mesozoic Era ended with the K-Pg Mass Extinction (previously known as the K-T Extinction ) 66 million years ago . This extinction event was likely caused by a large bolide ( an extraterrestrial impactor such as an asteroid, meteoroid, or comet) that collided with earth . Ninety percent of plankton species, 75% of plant species, and all the dinosaurs went extinct at this time.

Phanerozoic Eon: Cenozoic Era

8.8.1 Cenozoic Tectonics and Paleogeography

Animation of the last 38 million years of movement in western North America. Note, that after the ridge is subducted, convergent turns to transform (with divergent inland).

8.8.2 Cenozoic Evolution

Anthropocene and Extinction

The changes that have occurred since the inception of Earth are vast and significant. From the oxygenation of the atmosphere, the progression of life forms, the assembly and deconstruction of several supercontinents, to the extinction of more life forms than exist today, having a general understanding of these changes can put present change into a more rounded perspective.

Chapter Contents

• 1.1.1.1 Spectroscopy
• 1.1.1.2 Redshift
• 1.1.1.3 Cosmic Microwave Background Radiation
• 1.1.2.1 Birth of a star
• 1.1.2.2 Fusion
• 1.1.2.3 Death of a Star
• 1.2.1.1 Pluto and planet definition
• 1.3.1 Origin of Earth’s Crust
• 1.3.2 Origin of the Moon
• 1.3.3 Origin of Earth’s Water
• 1.4.1 Late Heavy Bombardment
• 1.4.2 Origin of the Continents
• 1.4.3 First Life on Earth
• 1.5.1 Rodinia
• 1.5.2 Life Evolves
• 1.6.1 Paleozoic Tectonics and Paleogeography
• 1.6.2.1 Permian Mass Extinction
• 1.7.1 8.7.1 Mesozoic Tectonics and Paleogeography
• 1.7.2.1 K-T Extinction
• 1.8.1 8.8.1 Cenozoic Tectonics and Paleogeography
• 1.8.2.1 Anthropocene and Extinction
• 1.9 Summary
• 1.10 References

July 1, 2005

19 min read

Evolution of Earth

The evolution of this planet and its atmosphere gave rise to life, which shaped Earth's subsequent development. Our future lies in interpreting this geologic past and considering what changes--good and bad--may lie ahead

By Claude J. Allègre & Stephen H. Schneider

Like the lapis lazuli gem it resembles, the blue, cloud-enveloped planet the we recognize immediately from satellite pictures seems remarkably stable. Continents and oceans, encircled by an oxygen-rich atmosphere, support familiar life-forms. Yet this constancy is an illusion produced by the human experience of time. Earth and its atmosphere are continuously altered. Plate tectonics shift the continents, raise mountains and move the ocean floor while processes not fully understood alter the climate.

Such constant change has characterized Earth since its beginning some 4.5 billion years ago. From the outset, heat and gravity shaped the evolution of the planet. These forces were gradually joined by the global effects of the emergence of life. Exploring this past offers us the only possibility of understanding the origin of life and, perhaps, its future.

Scientists used to believe the rocky planets, including Earth, Mercury, Venus and Mars, were created by the rapid gravitational collapse of a dust cloud, a deation giving rise to a dense orb. In the 1960s the Apollo space program changed this view. Studies of moon craters revealed that these gouges were caused by the impact of objects that were in great abundance about 4.5 billion years ago. Thereafter, the number of impacts appeared to have quickly decreased. This observation rejuvenated the theory of accretion postulated by Otto Schmidt. The Russian geophysicist had suggested in 1944 that planets grew in size gradually, step by step.

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

According to Schmidt, cosmic dust lumped together to form particulates, particulates became gravel, gravel became small balls, then big balls, then tiny planets, or planetesimals, and, nally, dust became the size of the moon. As the planetesimals became larger, their numbers decreased. Consequently, the number of collisions between planetesimals, or meteorites, decreased. Fewer items available for accretion meant that it took a long time to build up a large planet. A calculation made by George W. Wetherill of the Carnegie Institution of Washington suggests that about 100 million years could pass between the formation of an object measuring 10 kilometers in diameter and an object the size of Earth.

The process of accretion had significant thermal consequences for Earth, consequences that forcefully directed its evolution. Large bodies slamming into the planet produced immense heat in its interior, melting the cosmic dust found there. The resulting furnace--situated some 200 to 400 kilometers underground and called a magma ocean--was active for millions of years, giving rise to volcanic eruptions. When Earth was young, heat at the surface caused by volcanism and lava ows from the interior was intensified by the constant bombardment of huge objects, some of them perhaps the size of the moon or even Mars. No life was possible during this period.

Beyond clarifying that Earth had formed through accretion, the Apollo program compelled scientists to try to reconstruct the subsequent temporal and physical development of the early Earth. This undertaking had been considered impossible by founders of geology, including Charles Lyell, to whom the following phrase is attributed: No vestige of a beginning, no prospect for an end. This statement conveys the idea that the young Earth could not be re-created, because its remnants were destroyed by its very activity. But the development of isotope geology in the 1960s had rendered this view obsolete. Their imaginations red by Apollo and the moon ndings, geochemists began to apply this technique to understand the evolution of Earth.

Dating rocks using so-called radioactive clocks allows geologists to work on old terrains that do not contain fossils. The hands of a radioactive clock are isotopes--atoms of the same element that have different atomic weights--and geologic time is measured by the rate of decay of one isotope into another [see "The Earliest History of the Earth," by Derek York; Scientific American , January 1993]. Among the many clocks, those based on the decay of uranium 238 into lead 206 and of uranium 235 into lead 207 are special. Geochronologists can determine the age of samples by analyzing only the daughter product--in this case, lead--of the radioactive parent, uranium.

Panning for zircons ISOTOPE GEOLOGY has permitted geologists to determine that the accretion of Earth culminated in the differentiation of the planet: the creation of the core--the source of Earth's magnetic field--and the beginning of the atmosphere. In 1953 the classic work of Claire C. Patterson of the California Institute of Technology used the uranium-lead clock to establish an age of 4.55 billion years for Earth and many of the meteorites that formed it. In the early 1990s, however, work by one of us (Allègre) on lead isotopes led to a somewhat new interpretation.

As Patterson argued, some meteorites were indeed formed about 4.56 billion years ago, and their debris constituted Earth. But Earth continued to grow through the bombardment of planetesimals until some 120 million to 150 million years later. At that time--4.44 billion to 4.41 billion years ago--Earth began to retain its atmosphere and create its core. This possibility had already been suggested by Bruce R. Doe and Robert E. Zartman of the U.S. Geological Survey in Denver two decades ago and is in agreement with Wetherills estimates.

The emergence of the continents came somewhat later. According to the theory of plate tectonics, these landmasses are the only part of Earth's crust that is not recycled and, consequently, destroyed during the geothermal cycle driven by the convection in the mantle. Continents thus provide a form of memory because the record of early life can be read in their rocks. Geologic activity, however, including plate tectonics, erosion and metamorphism, has destroyed almost all the ancient rocks. Very few fragments have survived this geologic machine.

Nevertheless, in recent decades, several important nds have been made, again using isotope geochemistry. One group, led by Stephen Moorbath of the University of Oxford, discovered terrain in West Greenland that is between 3.7 billion and 3.8 billion years old. In addition, Samuel A. Bowring of the Massachusetts Institute of Technology explored a small area in North America--the Acasta gneiss--that is thought to be 3.96 billion years old.

Ultimately, a quest for the mineral zircon led other researchers to even more ancient terrain. Typically found in continental rocks, zircon is not dissolved during the process of erosion but is deposited in particle form in sediment. A few pieces of zircon can therefore survive for billions of years and can serve as a witness to Earths more ancient crust. The search for old zircons started in Paris with the work of Annie Vitrac and Jol R. Lancelot, later at the University of Marseille and now at the University of Nmes, respectively, as well as with the efforts of Moorbath and Allgre. It was a group at the Australian National University in Canberra, directed by William Compston, that was nally successful. The team discovered zircons in western Australia that were between 4.1 billion and 4.3 billion years old.

Zircons have been crucial not only for understanding the age of the continents but for determining when life rst appeared. The earliest fossils of undisputed age were found in Australia and South Africa. These relics of blue-green algae are about 3.5 billion years old. Manfred Schidlowski of the Max Planck Institute for Chemistry in Mainz studied the Isua formation in West Greenland and argued that organic matter existed as long ago as 3.8 billion years. Because most of the record of early life has been destroyed by geologic activity, we cannot say exactly when it rst appeared--perhaps it arose very quickly, maybe even 4.2 billion years ago.

Stories from gases ONE OF THE MOST important aspects of the planet's evolution is the formation of the atmosphere, because it is this assemblage of gases that allowed life to crawl out of the oceans and to be sustained. Researchers have hypothesized since the 1950s that the terrestrial atmosphere was created by gases emerging from the interior of the planet. When a volcano spews gases, it is an example of the continuous outgassing, as it is called, of Earth. But scientists have questioned whether this process occurred suddenly--about 4.4 billion years ago when the core differentiated--or whether it took place gradually over time.

To answer this question, Allègre and his colleagues studied the isotopes of rare gases. These gases--including helium, argon and xenon--have the peculiarity of being chemically inert, that is, they do not react in nature with other elements. Two of them are particularly important for atmospheric studies: argon and xenon. Argon has three isotopes, of which argon 40 is created by the decay of potassium 40. Xenon has nine, of which xenon 129 has two different origins. Xenon 129 arose as the result of nucleosynthesis before Earth and solar system were formed. It was also created from the decay of radioactive iodine 129, which does not exist on Earth anymore. This form of iodine was present very early on but has died out since, and xenon 129 has grown at its expense.

Like most couples, both argon 40 and potassium 40 and xenon 129 and iodine 129 have stories to tell. They are excellent chronometers. Although the atmosphere was formed by the outgassing of the mantle, it does not contain any potassium 40 or iodine 129. All argon 40 and xenon 129, formed in Earth and released, are found in the atmosphere today. Xenon was expelled from the mantle and retained in the atmosphere; therefore, the atmosphere-mantle ratio of this element allows us to evaluate the age of differentiation. Argon and xenon trapped in the mantle evolved by the radioactive decay of potassium 40 and iodine 129. Thus, if the total outgassing of the mantle occurred at the beginning of Earths formation, the atmosphere would not contain any argon 40 but would contain xenon 129.

The major challenge facing an investigator who wants to measure such ratios of decay is to obtain high concentrations of rare gases in mantle rocks because they are extremely limited. Fortunately, a natural phenomenon occurs at mid-ocean ridges during which volcanic lava transfers some silicates from the mantle to the surface. The small amounts of gases trapped in mantle minerals rise with the melt to the surface and are concentrated in small vesicles in the outer glassy margin of lava ows. This process serves to concentrate the amounts of mantle gases by a factor of 10 4 or 10 5 . Collecting these rocks by dredging the seaoor and then crushing them under vacuum in a sensitive mass spectrometer allows geochemists to determine the ratios of the isotopes in the mantle. The results are quite surprising. Calculations of the ratios indicate that between 80 and 85 percent of the atmosphere was outgassed during Earths rst one million years; the rest was released slowly but constantly during the next 4.4 billion years.

The composition of this primitive atmosphere was most certainly dominated by carbon dioxide, with nitrogen as the second most abundant gas. Trace amounts of methane, ammonia, sulfur dioxide and hydrochloric acid were also present, but there was no oxygen. Except for the presence of abundant water, the atmosphere was similar to that of Venus or Mars. The details of the evolution of the original atmosphere are debated, particularly because we do not know how strong the sun was at that time. Some facts, however, are not disputed. It is evident that carbon dioxide played a crucial role. In addition, many scientists believe the evolving atmosphere contained sufficient quantities of gases such as ammonia and methane to give rise to organic matter.

Still, the problem of the sun remains unresolved. One hypothesis holds that during the Archean eon, which lasted from about 4.5 billion to 2.5 billion years ago, the suns power was only 75 percent of what it is today. This possibility raises a dilemma: How could life have survived in the relatively cold climate that should accompany a weaker sun? A solution to the faint early sun paradox, as it is called, was offered by Carl Sagan and George Mullen of Cornell University in 1970. The two scientists suggested that methane and ammonia, which are very effective at trapping infrared radiation, were quite abundant. These gases could have created a super-greenhouse effect. The idea was criticized on the basis that such gases were highly reactive and have short lifetimes in the atmosphere.

What controlled co? IN THE LATE 1970s Veerabhadran Ramanathan, now at the Scripps Institution of Oceanography, and Robert D. Cess and Tobias Owen of Stony Brook University proposed another solution. They postulated that there was no need for methane in the early atmosphere because carbon dioxide was abundant enough to bring about the super-greenhouse effect. Again this argument raised a different question: How much carbon dioxide was there in the early atmosphere? Terrestrial carbon dioxide is now buried in carbonate rocks, such as limestone, although it is not clear when it became trapped there. Today calcium carbonate is created primarily during biological activity; in the Archean eon, carbon may have been primarily removed during inorganic reactions.

The rapid outgassing of the planet liberated voluminous quantities of water from the mantle, creating the oceans and the hydrologic cycle. The acids that were probably present in the atmosphere eroded rocks, forming carbonate-rich rocks. The relative importance of such a mechanism is, however, debated. Heinrich D. Holland of Harvard University believes the amount of carbon dioxide in the atmosphere rapidly decreased during the Archean and stayed at a low level.

Understanding the carbon dioxide content of the early atmosphere is pivotal to understanding climatic control. Two conicting camps have put forth ideas on how this process works. The rst group holds that global temperatures and carbon dioxide were controlled by inorganic geochemical feedbacks; the second asserts that they were controlled by biological removal.

James C. G. Walker, James F. Kasting and Paul B. Hays, then at the University of Michigan at Ann Arbor, proposed the inorganic model in 1981. They postulated that levels of the gas were high at the outset of the Archean and did not fall precipitously. The trio suggested that as the climate warmed, more water evaporated, and the hydrologic cycle became more vigorous, increasing precipitation and runoff. The carbon dioxide in the atmosphere mixed with rainwater to create carbonic acid runoff, exposing minerals at the surface to weathering. Silicate minerals combined with carbon that had been in the atmosphere, sequestering it in sedimentary rocks. Less carbon dioxide in the atmosphere meant, in turn, less of a greenhouse effect. The inorganic negative feedback process offset the increase in solar energy.

This solution contrasts with a second paradigm: biological removal. One theory advanced by James E. Lovelock, an originator of the Gaia hypothesis, assumed that photosynthesizing microorganisms, such as phytoplankton, would be very productive in a high carbon dioxide environment. These creatures slowly removed carbon dioxide from the air and oceans, converting it into calcium carbonate sediments. Critics retorted that phytoplankton had not even evolved for most of the time that Earth has had life. (The Gaia hypothesis holds that life on Earth has the capacity to regulate temperature and the composition of Earth's surface and to keep it comfortable for living organisms.)

In the early 1990s Tyler Volk of New York University and David W. Schwartzman of Howard University proposed another Gaian solution. They noted that bacteria increase carbon dioxide content in soils by breaking down organic matter and by generating humic acids. Both activities accelerate weathering, removing carbon dioxide from the atmosphere. On this point, however, the controversy becomes acute. Some geochemists, including Kasting, now at Pennsylvania State University, and Holland, postulate that while life may account for some carbon dioxide removal after the Archean, inorganic geochemical processes can explain most of the sequestering. These researchers view life as a rather weak climatic stabilizing mechanism for the bulk of geologic time.

Oxygen from algae THE ISSUE OF CARBON remains critical to how life inuenced the atmosphere. Carbon burial is a key to the vital process of building up atmospheric oxygen concentrations--a prerequisite for the development of certain life-forms. In addition, global warming is taking place now as a result of humans releasing this carbon. For one billion or two billion years, algae in the oceans produced oxygen. But because this gas is highly reactive and because there were many reduced minerals in the ancient oceans--iron, for example, is easily oxidized--much of the oxygen produced by living creatures simply got used up before it could reach the atmosphere, where it would have encountered gases that would react with it.

Even if evolutionary processes had given rise to more complicated life-forms during this anaerobic era, they would have had no oxygen. Furthermore, un ltered ultraviolet sunlight would have likely killed them if they left the ocean. Researchers such as Walker and Preston Cloud, then at the University of California at Santa Barbara, have suggested that only about two billion years ago, after most of the reduced minerals in the sea were oxidized, did atmospheric oxygen accumulate. Between one billion and two billion years ago oxygen reached current levels, creating a niche for evolving life.

By examining the stability of certain minerals, such as iron oxide or uranium oxide, Holland has shown that the oxygen content of the Archean atmosphere was low before two billion years ago. It is largely agreed that the present-day oxygen content of 20 percent is the result of photosynthetic activity. Still, the question is whether the oxygen content in the atmosphere increased gradually over time or suddenly. Recent studies indicate that the increase of oxygen started abruptly between 2.1 billion and 2.03 billion years ago and that the present situation was reached 1.5 billion years ago.

The presence of oxygen in the atmosphere had another major bene t for an organism trying to live at or above the surface: it ltered ultraviolet radiation. Ultraviolet radiation breaks down many molecules--from DNA and oxygen to the chlorouorocarbons that are implicated in stratospheric ozone depletion. Such energy splits oxygen into the highly unstable atomic form O, which can combine back into O 2 and into the very special molecule O 3 , or ozone. Ozone, in turn, absorbs ultraviolet radiation. It was not until oxygen was abundant enough in the atmosphere to allow the formation of ozone that life even had a chance to get a root-hold or a foothold on land. It is not a coincidence that the rapid evolution of life from prokaryotes (single-celled organisms with no nucleus) to eukaryotes (single-celled organisms with a nucleus) to metazoa (multicelled organisms) took place in the billion-year-long era of oxygen and ozone.

Although the atmosphere was reaching a fairly stable level of oxygen during this period, the climate was hardly uniform. There were long stages of relative warmth or coolness during the transition to modern geologic time. The composition of fossil plankton shells that lived near the ocean oor provides a measure of bottom water temperatures. The record suggests that over the past 100 million years bottom waters cooled by nearly 15 degrees Celsius. Sea levels dropped by hundreds of meters, and continents drifted apart. Inland seas mostly disappeared, and the climate cooled an average of 10 to 15 degrees C. Roughly 20 million years ago permanent ice appears to have built up on Antarctica.

About two million to three million years ago the paleoclimatic record starts to show signi cant expansions and contractions of warm and cold periods in 40,000-year or so cycles. This periodicity is interesting because it corresponds to the time it takes Earth to complete an oscillation of the tilt of its axis of rotation. It has long been speculated, and recently calculated, that known changes in orbital geometry could alter the amount of sunlight coming in between winter and summer by about 10 percent or so and could be responsible for initiating or ending ice ages.

The warm hand of man MOST INTERESTING and perplexing is the discovery that between 600,000 and 800,000 years ago the dominant cycle switched from 40,000-year periods to 100,000-year intervals with very large uctuations. The last major phase of glaciation ended about 10,000 years ago. At its height 20,000 years ago, ice sheets about two kilometers thick covered much of northern Europe and North America. Glaciers expanded in high plateaus and mountains throughout the world. Enough ice was locked up on land to cause sea levels to drop more than 100 meters below where they are today. Massive ice sheets scoured the land and revamped the ecological face of Earth, which was ve degrees C cooler on average than it is currently.

The precise causes of the longer intervals between warm and cold periods are not yet sorted out. Volcanic eruptions may have played a signi cant role, as shown by the effect of El Chichón in Mexico and Mount Pinatubo in the Philippines. Tectonic events, such as the development of the Himalayas, may have inuenced world climate. Even the impact of comets can inuence short-term climatic trends with catastrophic consequences for life [see "What Caused the Mass Extinction? An Extraterrestrial Impact," by Walter Alvarez and Frank Asaro; and "What Caused the Mass Extinction? A Volcanic Eruption," by Vincent E. Courtillot; Scientific American , October 1990]. It is remarkable that despite violent, episodic perturbations, the climate has been buffered enough to sustain life for 3.5 billion years.

One of the most pivotal climatic discoveries of the past 30 years has come from ice cores in Greenland and Antarctica. When snow falls on these frozen continents, the air between the snow grains is trapped as bubbles. The snow is gradually compressed into ice, along with its captured gases. Some of these records can go back more than 500,000 years; scientists can analyze the chemical content of ice and bubbles from sections of ice that lie as deep as 3,600 meters (2.2 miles) below the surface.

The ice-core borers have determined that the air breathed by ancient Egyptians and Anasazi Indians was very similar to that which we inhale today--except for a host of air pollutants introduced over the past 100 or 200 years. Principal among these added gases, or pollutants, are extra carbon dioxide and methane. Since about 1860--the expansion of the Industrial Revolution--carbon dioxide levels in the atmosphere have increased more than 30 percent as a result of industrialization and deforestation; methane levels have more than doubled because of agriculture, land use and energy production. The ability of increased amounts of these gases to trap heat is what drives concerns about climate change in the 21st century [see "The Changing Climate," by Stephen H. Schneider; Scientific American , September 1989].

The ice cores have shown that sustained natural rates of worldwide temperature change are typically about one degree C per millennium. These shifts are still signi cant enough to have radically altered where species live and to have potentially contributed to the extinction of such charismatic megafauna as mammoths and saber-toothed tigers. But a most extraordinary story from the ice cores is not the relative stability of the climate during the past 10,000 years. It appears that during the height of the last ice age 20,000 years ago there was 50 percent less carbon dioxide and less than half as much methane in the air than there has been during our epoch, the Holocene. This nding suggests a positive feedback between carbon dioxide, methane and climatic change.

The reasoning that supports the idea of this destabilizing feedback system goes as follows. When the world was colder, there was less concentration of greenhouse gases, and so less heat was trapped. As Earth warmed up, carbon dioxide and methane levels increased, accelerating the warming. If life had a hand in this story, it would have been to drive, rather than to oppose, climatic change. It appears increasingly likely that when humans became part of this cycle, they, too, helped to accelerate warming. Such warming has been especially pronounced since the mid-1800s because of greenhouse gas emissions from industrialization, land-use change and other phenomena. Once again, though, uncertainties remain.

Nevertheless, most scientists would agree that life could well be the principal factor in the positive feedback between climatic change and greenhouse gases. There was a rapid rise in average global surface temperature at the end of the 20th century [ see illustration on opposite page ]. Indeed, the period from the 1980s onward has been the warmest of the past 2,000 years. Nineteen of the 20 warmest years on record have occurred since 1980, and the 12 warmest have all occurred since 1990. The all-time record high year was 1998, and 2002 and 2003 were in second and third places, respectively. There is good reason to believe that the decade of the 1990s would have been even hotter had not Mount Pinatubo erupted: this volcano put enough dust into the high atmosphere to block some incident sunlight, causing global cooling of a few tenths of a degree for several years.

Could the warming of the past 140 years have occurred naturally? With ever increasing certainty, the answer is no.

The box at the right shows a remarkable study that attempted to push back the Northern Hemisphere's temperature record a full 1,000 years. Climatologist Michael Mann of the University of Virginia and his colleagues performed a complex statistical analysis involving some 112 different factors related to temperature, including tree rings, the extent of mountain glaciers, changes in coral reefs, sunspot activity and volcanism.

The resulting temperature record is a reconstruction of what might have been obtained had thermometer-based measurements been available. (Actual temperature measurements are used for the years after 1860.) As shown by the confidence range, there is considerable uncertainty in each year of this 1,000-year temperature reconstruction. But the overall trend is clear: a gradual temperature decrease over the first 900 years, followed by a sharp temperature upturn in the 20th century. This graph suggests that the decade of the 1990s was not only the warmest of the century but of the entire past millennium.

By studying the transition from the high carbon dioxide, low-oxygen atmosphere of the Archean to the era of great evolutionary progress about half a billion years ago, it becomes clear that life may have been a factor in the stabilization of climate. In another example--during the ice ages and interglacial cycles--life seems to have the opposite function: accelerating the change rather than diminishing it. This observation has led one of us (Schneider) to contend that climate and life coevolved rather than life serving solely as a negative feedback on climate.

If we humans consider ourselves part of life--that is, part of the natural system--then it could be argued that our collective impact on Earth means we may have a signi cant co-evolutionary role in the future of the planet. The current trends of population growth, the demands for increased standards of living and the use of technology and organizations to attain these growth-oriented goals all contribute to pollution. When the price of polluting is low and the atmosphere is used as a free sewer, carbon dioxide, methane, chlorouorocarbons, nitrous oxides, sulfur oxides and other toxics can build up.

Drastic changes ahead IN THEIR REPORT Climate Change 2001 , climate experts on the Intergovernmental Panel on Climate Change estimated that the world will warm between 1.4 and 5.8 degrees C by 2100. The mild end of that range--a warming rate of 1.4 degrees C per 100 years--is still 14 times faster than the one degree C per 1,000 years that historically has been the average rate of natural change on a global scale. Should the higher end of the range occur, then we could see rates of climatic change nearly 60 times faster than natural average conditions, which could lead to changes that many would consider dangerous. Change at this rate would almost certainly force many species to attempt to move their ranges, just as they did from the ice age/interglacial transition between 10,000 and 15,000 years ago. Not only would species have to respond to climatic change at rates 14 to 60 times faster, but few would have undisturbed, open migration routes as they did at the end of the ice age and the onset of the interglacial era. The negative effects of this significant warming--on health, agriculture, coastal geography and heritage sites, to name a few--could also be severe.

To make the critical projections of future climatic change needed to understand the fate of ecosystems on Earth, we must dig through land, sea and ice to learn as much from geologic, paleoclimatic and paleoecological records as we can. These records provide the backdrop against which to calibrate the crude instruments we must use to peer into a shadowy environmental future, a future increasingly inuenced by us.

THE AUTHORS CLAUDE J. ALLGRE and STEPHEN H. SCHNEIDER study various aspects of Earths geologic history and its climate. Allgre is professor at the University of Paris and directs the department of geochemistry at the Paris Geophysical Institute. He is a foreign member of the National Academy of Sciences. Schneider is professor in the department of biological sciences at Stanford University and co-director of the Center for Environmental Science and Policy. He was honored with a MacArthur Prize Fellowship in 1992 and was elected to membership in the National Academy of Sciences in 2002.

Earth’s Geologic History and Global Climate Change Essay

Geologic history of earth, global climate change, drawing conclusions.

Using the Museum of Paleontology website (University of California, 2014), I found six significant events listed when I clicked on “bookmarks” in the tutorial: formation of the Earth and Moon 4.6 billion years ago, the appearance of the earliest life 3.9 billion years ago, the appearance of the earliest land plants 420 million years ago, the largest mass extinction 248 million years ago, dinosaur extinction 65 million years ago, and early hominid (“Lucy”) appearance 4 million years ago.

In the Geologic Time Scale section of the Museum of Paleontology website (University of California, 2014), I found that images of cyanobacteria are included in the Archaean time period. Besides, I discovered that there are three Eras in the history of the Earth: Paleozoic, Mesozoic, and Cenozoic. The Eras’ representative organisms are the following: brachiopods, progymnosperms, and trilobites for Paleozoic Era; conifers, cycads, birds, and dinosaurs For Mesozoic Era; flowering plants, saber-toothed cats, megaloceroses, and mammoths For Cenozoic Era (University of California, 2014).

In the Sam Noble Museum Mass Extinctions website (Sam Noble Museum, 2017), five major mass extinction periods listed: End-Ordovician, Late Devonian, End-Permian, End-Triassic, and End-Cretaceous. The End-Ordovician extinction was caused by a major ice age. Species from trilobites, brachiopods, corals, crinoids, and graptolites groups disappeared. The Late Devonian extinction occurred due to the cooling of the global climate. In this extinction, stromatoporoids, brachiopods, and a lot of trilobites’ species disappeared. The End-Permian extinction was connected to the global climate warming caused by intense volcanic activity. During this extinction, trilobites and tabulate and rugose corals completely disappeared, as well as a lot of species of rhynchonelliform brachiopods, crinoids, shelled cephalopods, and snails.

In the End-Triassic extinction, a lot of species of marine invertebrate groups, including brachiopods, shelled cephalopods, sponges, and corals disappeared as well as a group of land-living phytosaurs. It is believed that the main cause of extinction was climate change. The vast continent Pangea began to break. As a result, the volcanic activity increased, and a major scale of carbon dioxide was introduced into the atmosphere which led to global warming.

In the End-Cretaceous extinction, non-avian dinosaurs, flying pterosaurs, mosasaurs, plesiosaurs, and ichthyosaurs as well as marine invertebrates, including ammonites and some cephalopods and bivalves disappeared. It is believed that the reason for this event is the Earth’s collision with an asteroid and the dust release to the atmosphere (Sam Noble Museum, 2017).

I discovered that human activities which include burning of fossil flues (coal and oil) are related to greenhouse gas production. These activities increase the rate at which carbon is returned to the atmosphere (Pearson education, n.d.a).

From the Greenhouse Gas Simulation (Pearson education, n.d.b), I learned that the relation between temperature and percent greenhouse gases amount is directly proportional (higher gases emission leads to a higher temperature), while the relation between the percentage of gases and ice is inversely proportional (higher gases emission leads to decrease of the ice area).

The current situation reminds me of the End-Permian extinction. It was stated that this extinction was caused by volcanic activity. Carbon dioxide released into the atmosphere during eruptions. Moreover, released lava heated carbon-reach rocks which also led to greenhouse gas production (Sam Noble Museum, 2017).

It could be stated that humans’ activities connected to coal and oil burning currently lead to greenhouse gases emission and global warming.

Based on the provided information, it could be concluded that the history of the Earth includes five mass extinctions. All of the extinctions are connected to global climate changes. Nowadays, human activities cause greenhouse gases emission which leads to climate warming and might result in the sixth extinction. The history of the Earth was estimated using the geologic time scale based on fossil records. Still, it is not entirely clear if humans’ activities are the main reason for climate change or this process is a part of the natural temperature fluctuation.

Pearson education. (n.d.a). The carbon cycle and global warming . Web.

Pearson education. (n.d.b). The greenhouse effect . Web.

Sam Noble Museum. (2017). Extinctions in the recent past and the present day. Web.

University of California, Berkeley, Museum of Paleontology. (n.d.). Geologic time . Web.

• Chicago (A-D)
• Chicago (N-B)

IvyPanda. (2020, September 29). Earth's Geologic History and Global Climate Change. https://ivypanda.com/essays/earths-geologic-history-and-global-climate-change/

"Earth's Geologic History and Global Climate Change." IvyPanda , 29 Sept. 2020, ivypanda.com/essays/earths-geologic-history-and-global-climate-change/.

IvyPanda . (2020) 'Earth's Geologic History and Global Climate Change'. 29 September.

IvyPanda . 2020. "Earth's Geologic History and Global Climate Change." September 29, 2020. https://ivypanda.com/essays/earths-geologic-history-and-global-climate-change/.

1. IvyPanda . "Earth's Geologic History and Global Climate Change." September 29, 2020. https://ivypanda.com/essays/earths-geologic-history-and-global-climate-change/.

Bibliography

IvyPanda . "Earth's Geologic History and Global Climate Change." September 29, 2020. https://ivypanda.com/essays/earths-geologic-history-and-global-climate-change/.

• Anthropocene and Human Impact on Environment
• Geology of Palouse Falls
• Geologic Events Log 2008-2009
• Geoengineering as a Possible Response to Climate Change
• Climate Change: Ways of Eliminating Negative Effects
• Climate Change Probability and Predictions
• Climate Changes and Human Population Distribution
• Climate Economists’ Input Into Planet Protection

The History of Earth in Exactly 2000 Words

The history of Earth is obviously a ginormous topic. Really, almost everything humans know is part of the history of Earth. Here, we will cover the geologic and biologic history of Earth, dating all the way back to its creation. Given that earth formed 4.6 billion years old and I only have 2000 words to cover the entire history of earth, this will necessarily be a sweeping overview. We’ve got to cover 2 million years per word!

Pre-Earth – Solar System Formation

The universe is 14 billion years old. Earth, in contrast, is merely a third of that age. The earth’s formation occurred around the team time as our solar system’s formation. 

Our solar system was probably caused by the supernova of another star. A supernova is an incredibly powerful explosion of a star. That explosion creates a shock wave that travels outwards. The  solar nebula hypothesis  proposes that the shockwave from a supernova swept up any space dust that was out in the ether towards the front of a sort of wave. Think of it like sweeping up dust from your floor. As all of this dust, which was spread out over unimaginable distances, becomes (relatively) concentrated in one area at the front of the shock wave, the gravitational pull from each piece of dust began to pull the dust together. This process is called accretion. Accretion continued and the dust turned into rocks, which turned into asteroids, and got bigger until our planet and sun formed. 

Geologic Time

Geologists break time into geologic time. Eons are the largest units on the geologic time scale, lasting 500 million to 2 billion years. Smaller units of time are eras, periods, and epochs. For example, we are in the Holocene epoch, which is part of the Quaternary period, which is part of the Cenozoic era, which is part of the Phanerozoic eon. Here, we will explore planet Earth’s four eons in broad strokes.

Hadean Eon – Hell on Earth 

4.6 – 4 billion years ago

The first eon in the history of Earth was the Hadean Eon. The earth’s surface was a molten ball of magma during this eon. The Hadean eon was incredibly violent, with lots of major impacts from accretion still happening. 

Theia and Our Moon

One particularly noteworthy impact was when the planetary body Theia dealt a glancing blow to early Earth. Both celestial bodies were molten.  When Theia hit Earth , Theia tore off a chunk of Earth’s mass. Theia continued on her orbit, but the torn-off chunk of Earth did not. As it cooled, this chunk remained in the Earth’s orbit and turned into our moon. 

As with everything in geologic time, scientists are currently  rethinking  the creation of the moon, with some arguing that it wasn’t Theia’s impact. 

The Late Heavy Bombardment

The  late heavy bombardment  marks the end of Hadean eon and the beginning of the next eon, which is the Archean. The late heavy bombardment was caused when gas giants Uranus and Neptune fled further away from the sun. This change in solar system gravity caused tons of asteroids, comets, and meteorites from the asteroid belt to be pulled closer towards the sun, and therefore Earth. Tons and tons of these asteroids impacted Earth, Venus, Mars, and Mercury. These collisions made Earth gain mass and heat.  

We have no rocks from the Hadean Eon because the Earth was all lava. Scientists believe life couldn’t have formed before the incredibly riotous time of the late heavy bombardment.

Archean Eon – The Origins of Life

4 – 2.5 billion years ago

The Archean Eon wasn’t nearly as violent as the Hadean, but Earth still wasn’t a place you would want to visit. After the late heavy bombardment, the crust of the earth was able to solidify into a rock, rather than magma. Earth had no atmosphere and the land was completely inhospitable. 

The First Fossils, the First Life

The first fossils of life on earth appear about  4-3.7 billion years ago  during the first part of the Archean era. Of course, early life was incredibly basic compared to what we’re used to today. Viruses also appeared around this time.  Some scientists  think the relatively rapid appearance of living organisms on earth, being only a few hundred million years after the planet itself appeared, is evidence supporting the existence of life all over the universe. The  oldest fossils  we know about are in Australia and date to 3.5 billion years ago. 

Photosynthesis Begins

About 3.5 billion years ago, life figured out how to capture energy from the sun via photosynthesis. These ocean-dwelling microbes released oxygen as a byproduct. However, this oxygen didn’t help create an atmosphere just yet. Instead, the high concentration of iron in the oceans reacted with the oxygen, preventing it from escaping out of the ocean. 

Proterozoic Eon – Something and Then Nothing

2.5 billion – 550 million years ago

The Proterozoic eon is, by far, the longest in Earth’s history, at about 2 billion years. Earth’s atmosphere and lithosphere (rocks) changed significantly during the first part of this period. The second billion years of the Proterozoic, in contrast, were not very exciting.

The Great Oxygenation 

Oxygen began to accumulate in Earth’s atmosphere  around 2.3 billion years ago . The accumulation of oxygen distinguishes the Archaean Eon from the Proterozoic Eon. 

The first snowball Earth occurred during this time. This glaciation was one of the major drivers that pumped oxygen into the atmosphere. When climate change caused the end of this ice age around 2.3 billion years ago, the melting ice introduced vast amounts of oxygen into the atmosphere.

Ironically, the addition of oxygen to the oceans and atmosphere was catastrophic for life on Earth, at least in the short run. Life in the oceans had evolved to live in an anaerobic, or oxygen-free, environment. The introduction of oxygen led to the extinction of many of these anaerobic bacteria. 

The Boring Billion

As the name implies, the period from about 1.8 to 0.8 billion years ago was remarkable in only one way; that Earth was stable and not much happened. Tectonics didn’t shift much, life didn’t really evolve, there weren’t many available nutrients, and the climate didn’t change. 

Some scientists think that eukaryotes (life with a nucleus) evolved all-important characteristics during the boring billion, such as sexual reproduction, which made the Cambrian explosion possible. Additionally, algae and the beginnings of plants evolved during this time. But considering this was over 1000 million years, those evolutionary accomplishments seem fairly minimal. I guess all of us, the Earth included, need periods of rest. 

Plate Tectonics

Geologists aren’t exactly sure when the Earth’s crust divided into different plates, causing plate tectonics. This may have happened anywhere from  1-3 billion years ago . Scientists who argue for the more recent evolution of plate tectonics believe that this process  couldn’t have happened  when the Earth was still a ball of magma or otherwise very hot. Ever since the late heavy bombardment, the earth has been cooling. As the crust of the earth turned from magma to rock, tectonic plates were able to form. 

Plate tectonics has been  essential to the development of life on Earth  over the past billion years. These tectonics create mountain ranges and oceanic troughs. Along with glaciers that crushed rocks, the eroding of mountains made via plate tectonics provided the nutrients necessary for life to finally end the boring billion. 

Phanerozoic Eon – Our Modern Earth

550 million years ago to present

All the nutrients pouring into the ocean from eroding mountains provided the building blocks for life to diversify. The beginning of the Phanerozoic Eon is marked by the  Cambrian Explosion . Tons of exciting life forms first appeared during this time. Importantly for us, the first animals evolved during this biological explosion. While we don’t have fossils of the very first animals, creatures like  hallucigenia  and jellyfish give us clues into the first animals that swam (they were all sea-dwelling) the earth. Here are just a  few examples  of new life that evolved during the explosion; sea creatures evolved eyes and legs, mollusks appeared, predators evolved jaws and teeth, and worms evolved plume-like gills. 

Complex Plants!

About 470 million years ago plants finally made the move from the ocean to land. About 100 million years later, these plants began to resemble the plants we have today with roots, leaves, and stems. Fun fact: grass hadn’t evolved by the time dinosaurs walked the Earth. 

Supercontinents – A Crucial Step in the History of the Earth

The formation and breakup of the  supercontinents Gondwana and Pangea  had massive impacts on the history of the earth. The size of landmass, the location of that landmass relative to the poles of the earth, and the volcanic activity of that landmass all contributed to the different climates of the Phanerozoic eon. 

Dinosaurs – The Mesozoic Era

Of course, dinosaurs are an integral part of the history of Earth and our current eon. Dinos evolved about 250 million years ago and dominated the earth until 66 million years ago. You may recognize the words Triassic, Jurassic, and Cretaceous. These are all periods of geologic time, which are smaller than eras, which in turn are smaller than eons. Dinosaurs roamed during these three geologic periods, which together make the Mesozoic era. 

Mass Extinctions

Since the Cambrian explosion, there have been six mass extinctions ( including the human-caused one happening today ). These extinctions were major events in the evolution of life because they culled down the number of species on the planet. Over the next tens of millions of years, new forms of life evolved from those that made it through the extinction, eventually leading to the world of life we know today.

Humans Evolve – The Antropocene

Some people speak of evolution as if the appearance of humans was the end goal of evolution. Evolution has no goals and will continue long after humans go extinct. We are merely a byproduct of natural processes. As demonstrated above, if the age of the earth was condensed into 12 hours, humans would appear 11 hours 59 minutes 58 seconds into that 12 hours. Our presence is  very  new to this planet. 

However, a history of Earth necessarily ends with the evolution of homo sapiens because that’s where we are today. Some scientists are fighting for the Anthropocene to become our present-day geologic epoch. This geologic period would start after World War II, when humans began to change the climate and create vast amounts of waste, especially plastic. Evidence for this new geologic period is the presence of plastic all over the world, which will eventually become incorporated into rocks and earth’s lithosphere, the rapid warming of the planet, and the mass extinction event happening currently. 

Geologists as a whole haven’t accepted the designation of the Anthropocene as its own geologic period, but that may change in the coming years. 

What can early Earth teach us about the search for life?

by Evan Gough, Universe Today

Earth is the only life-supporting planet we know of, so it's tempting to use it as a standard in the search for life elsewhere. But the modern Earth can't serve as a basis for evaluating exoplanets and their potential to support life. Earth's atmosphere has changed radically over its 4.5 billion years.

A better way is to determine what biomarkers were present in Earth's atmosphere at different stages in its evolution and judge other planets on that basis.

That's what a group of researchers from the UK and the U.S. did. Their research is titled " The early Earth as an analogue for exoplanetary biogeochemistry ," and it appears on the pre-print server arXiv . The lead author is Eva E. Stüeken, a Ph.D. student at the School of Earth & Environmental Sciences, University of St Andrews, UK.

When Earth formed about 4.5 billion years ago, its atmosphere was nothing like it is today. At that time, the atmosphere and oceans were anoxic. About 2.4 billion years ago, free oxygen began to accumulate in the atmosphere during the Great Oxygenation Event, one of the defining periods in Earth's history. But the oxygen came from life itself, meaning life was present when the Earth's atmosphere was much different.

This isn't the only example of how Earth's atmosphere has changed over geological time . But it's an instructive one and shows why searching for life means more than just searching for an atmosphere like modern Earth's. If that's the way we conducted the search, we'd miss worlds where photosynthesis hadn't yet appeared.

In their research, the authors point out how Earth hosted a rich and evolving population of microbes under different atmospheric conditions for billions of years.

"For most of this time, Earth has been inhabited by a purely microbial biosphere albeit with seemingly increasing complexity over time," the authors write. "A rich record of this geobiological evolution over most of Earth's history thus provides insights into the remote detectability of microbial life under a variety of planetary conditions."

It's not just life that's changed over time. Plate tectonics have changed and may have been 'stagnant lid' tectonics for a long time. In stagnant lid tectonics, plates don't move horizontally. That can have consequences for atmospheric chemistry.

The main point is that Earth's atmosphere does not reflect the solar nebula the planet formed in. Multiple intertwined processes have changed the atmosphere over time. The search for life involves not only a better understanding of these processes, but how to identify what stage exoplanets might be in.

It's axiomatic that biological processes can have a dramatic effect on planetary atmospheres. "On the modern Earth, the atmospheric composition is very strongly controlled by life," the researchers write. "However, any potential atmospheric biosignature must be disentangled from a backdrop of abiotic (geological and astrophysical) processes that also contribute to planetary atmospheres and would be dominating on lifeless worlds and on planets with a very small biosphere."

The authors outline what they say are the most important lessons that the early Earth can teach us about the search for life.

The first is that the Earth has actually had three different atmospheres throughout its long history. The first one came from the solar nebula and was lost soon after the planet formed. That's the primary atmosphere. The second one formed from outgassing from the planet's interior.

The third one, Earth's modern atmosphere, is complex. It's a balancing act involving life, plate tectonics, volcanism, and even atmospheric escape. A better understanding of how Earth's atmosphere has changed over time gives researchers a better understanding of what they see in exoplanet atmospheres.

The second is that the further we look back in time, the more the rock record of Earth's early life is altered or destroyed. Our best evidence suggests life was present by 3.5 billion years ago, maybe even by 3.7 billion years ago. If that's the case, the first life may have existed on a world covered in oceans, with no continental land masses and only volcanic islands.

If there had been abundant volcanic and geological activity between 3.5 and 3.7 billion years ago, there would've been large fluxes of CO 2 and H 2 . Since these are substrates for methanogenesis, then methane may have been abundant in the atmosphere and detectable.

The third lesson the authors outline is that a planet can host oxygen-producing life for a long time before oxygen can be detected in an atmosphere. Scientists think that oxygenic photosynthesis appeared on Earth in the mid-Archean eon. The Archean spanned from 4 billion to 2.5 billion years ago, so mid-Archean is sometime around 3.25 billion years ago. But oxygen couldn't accumulate in the atmosphere until the Great Oxygenation Event about 2.4 billion years ago.

Oxygen is a powerful biomarker, and if it is found in an exoplanet's atmosphere, it would be cause for excitement. But life on Earth was around for a long time before atmospheric oxygen would've been detectable.

The fourth lesson involves the appearance of horizontal plate tectonics and its effect on chemistry. "From the GOE onwards, the Earth looked tectonically similar to today," the authors write. The oceans were likely stratified into an anoxic layer and an oxygenated surface layer. However, hydrothermal activity constantly introduced ferrous iron into the oceans. That increased the sulfate levels in the seawater which reduced the methane in the atmosphere. Without that methane, Earth's biosphere would've been much less detectable.

"Planet Earth has evolved over the past 4.5 billion years from an entirely anoxic planet with possibly a different tectonic regime to the oxygenated world with horizontal plate tectonics that we know today," the authors explain. All that complex evolution allowed life to appear and to thrive, but it also makes detecting earlier biospheres on exoplanets more complicated.

We're at a huge disadvantage in the search for life on exoplanets. We can literally dig into Earth's ancient rock to try to untangle the long history of life on Earth and how the atmosphere evolved over billions of years. When it comes to exoplanets, all we have is telescopes. Increasingly powerful telescopes, but telescopes nonetheless. While we are beginning to explore our own solar system, especially Mars and the tantalizing ocean moons orbiting the gas giants, other solar systems are beyond our physical reach.

"We must instead remotely recognize the presence of alien biospheres and characterize their biogeochemical cycles in planetary spectra obtained with large ground- and space-based telescopes," the authors write. "These telescopes can probe atmospheric composition by detecting absorption features associated with specific gases." Probing atmospheric gases is our most powerful approach right now, as the JWST shows.

But as scientists get better tools, they'll start to go beyond atmospheric chemistry. "We might also be able to recognize global-scale surface features, including light interaction with photosynthetic pigments and 'glint' arising from specular reflection of light by a liquid ocean."

Understanding what we're seeing in exoplanet atmospheres parallels our understanding of Earth's long history. Earth could be the key to our broadening and accelerating search for life.

"Unraveling the details of Earth's complex biogeochemical history and its relationship with remotely observable spectral signals is an important consideration for instrument design and our own search for life in the universe," the authors write.

Provided by Universe Today

Explore further

Feedback to editors

Scientists create an 'optical conveyor belt' for quasiparticles

40 minutes ago

Scientists develop sticky pesticide to combat pest insects

46 minutes ago

Researchers precisely characterize styrene oxide isomerase, which could help yield 'green' chemicals and drug precursors

4 hours ago

Exploring the ultrasmall and ultrafast through advances in attosecond science

15 hours ago

Machine learning and AI aid in predicting molecular selectivity of chemical reactions

Persistent strain of cholera defends itself against forces of change, scientists find

16 hours ago

Study reveals insights into protein evolution

Scientists help unravel life's cosmic beginnings

Physicists create five-lane superhighway for electrons

Fruit fly testes offer potential tool against harmful insects

17 hours ago

Relevant PhysicsForums posts

Our beautiful universe - photos and videos.

2 hours ago

Solar Activity and Space Weather Update thread

8 hours ago

Strange cosmic particles in my detector

May 13, 2024

U.S. Solar Eclipses - Oct. 14, 2023 (Annular) & Apr. 08, 2024 (Total)

May 12, 2024

Exploring the Sun: Amateur Solar Imaging Techniques

Dark matter and its effect on the orbit of stars.

More from Astronomy and Astrophysics

Related Stories

Webb telescope probably didn't find life on an exoplanet—yet

May 2, 2024

Will we know if TRAPPIST-1e has life?

Apr 23, 2024

Is it life, or is it volcanoes?

Sep 29, 2023

Life might be easiest to find on planets that match an earlier Earth

Nov 17, 2023

Earth holds the key to detecting life beyond our solar system

Feb 19, 2018

If a planet has a lot of methane in its atmosphere, life is the most likely cause

Dec 24, 2020

Recommended for you

Discovery of biomarkers in space—conditions on Saturn's moon Enceladus simulated in the laboratory

21 hours ago

Tracing the origins of organic matter in Martian sediments

22 hours ago

Student's comparative analysis of primitive asteroids provides context for further research, future NASA missions

AI may be to blame for our failure to make contact with alien civilizations

May 11, 2024

Solar storm puts on brilliant light show across the globe, but no serious problems reported

Let us know if there is a problem with our content.

Use this form if you have come across a typo, inaccuracy or would like to send an edit request for the content on this page. For general inquiries, please use our contact form . For general feedback, use the public comments section below (please adhere to guidelines ).

Please select the most appropriate category to facilitate processing of your request

Thank you for taking time to provide your feedback to the editors.

Your feedback is important to us. However, we do not guarantee individual replies due to the high volume of messages.

E-mail the story

Your email address is used only to let the recipient know who sent the email. Neither your address nor the recipient's address will be used for any other purpose. The information you enter will appear in your e-mail message and is not retained by Phys.org in any form.

Newsletter sign up

Get weekly and/or daily updates delivered to your inbox. You can unsubscribe at any time and we'll never share your details to third parties.

More information Privacy policy

Donate and enjoy an ad-free experience

We keep our content available to everyone. Consider supporting Science X's mission by getting a premium account.

E-mail newsletter

The Ordovician-Silurian Extinction: a Turning Point in Earth’s History

This essay about the Ordovician-Silurian extinction event examines one of Earth’s most devastating periods of biodiversity loss, occurring around 443 million years ago. It explores the causes and consequences of this extinction, emphasizing its profound impact on marine ecosystems and the subsequent evolutionary trajectory of life on our planet. By understanding this ancient event, scientists gain insights into the intricate relationship between Earth’s systems and the life it sustains, offering valuable lessons for addressing current environmental challenges and safeguarding biodiversity.

How it works

The Ordovician-Silurian extinction event, occurring approximately 443 million years ago, marks one of the most devastating periods of biodiversity loss in Earth’s history. This event dramatically reshaped the composition of marine ecosystems and had long-lasting effects on the evolutionary trajectory of life on our planet. Understanding this ancient extinction helps scientists appreciate the complex interplay between Earth’s systems and the life it supports.

The Ordovician-Silurian extinction unfolded in two distinct phases, each characterized by massive environmental upheaval and significant biological turnover.

The first phase, which marked the end of the Ordovician Period, saw the extinction of an estimated 85% of marine species. This was followed by a less severe but still substantial second wave during the early Silurian Period. The marine communities that once thrived, including trilobites, brachiopods, and bryozoans, were drastically reduced, paving the way for other groups to rise in prominence.

Several factors contributed to this biotic crisis, with changes in climate and sea levels playing central roles. The end of the Ordovician was marked by a severe ice age that locked much of the planet’s water in ice caps, leading to dramatic drops in sea levels. These changes disrupted marine habitats extensively, particularly affecting the shallow warm-water environments where many organisms thrived. The glaciation likely altered ocean currents, which in turn affected the oxygen and nutrient dynamics critical for marine life.

Furthermore, there is evidence suggesting that volcanic activity might have played a role in triggering some of these environmental changes. The release of volcanic gases could have contributed to an initial greenhouse effect that warmed the planet, only to be followed by rapid cooling as the gases dissipated and dust and aerosols blocked sunlight. This rapid climatic shift would have placed immense stress on ecosystems that were already sensitive to change.

Despite the severity of the extinction, it set the stage for evolutionary innovation and diversification. The post-extinction recovery period saw the emergence and radiation of new species adapted to the altered environments. For instance, fish began to diversify, and new types of coral reefs started to form, indicating a significant shift in marine ecological structures. These changes underscore the dynamic nature of life on Earth and its ability to adapt to even the most challenging conditions.

Studying the Ordovician-Silurian extinction not only informs us about past biological crises but also serves as a poignant reminder of the fragility of ecosystems in the face of rapid environmental changes. Today, as we face our own environmental challenges, including climate change and biodiversity loss, lessons from the distant past can provide valuable insights. Understanding how life on Earth responded to past mass extinctions can help us predict potential outcomes and develop strategies to mitigate the impacts of current environmental stresses.

In summary, the Ordovician-Silurian extinction event was a defining moment in Earth’s history, highlighting the vulnerability and resilience of life. Through the lens of this ancient catastrophe, we gain perspective on the potential long-term impacts of our current ecological footprint and are reminded of the continuous interplay between life and the environmental conditions that sustain it. Such historical insights are crucial as we seek to safeguard biodiversity and ensure the stability of life-supporting systems on our planet.

Cite this page

The Ordovician-Silurian Extinction: A Turning Point in Earth's History. (2024, May 12). Retrieved from https://papersowl.com/examples/the-ordovician-silurian-extinction-a-turning-point-in-earths-history/

"The Ordovician-Silurian Extinction: A Turning Point in Earth's History." PapersOwl.com , 12 May 2024, https://papersowl.com/examples/the-ordovician-silurian-extinction-a-turning-point-in-earths-history/

PapersOwl.com. (2024). The Ordovician-Silurian Extinction: A Turning Point in Earth's History . [Online]. Available at: https://papersowl.com/examples/the-ordovician-silurian-extinction-a-turning-point-in-earths-history/ [Accessed: 14 May. 2024]

"The Ordovician-Silurian Extinction: A Turning Point in Earth's History." PapersOwl.com, May 12, 2024. Accessed May 14, 2024. https://papersowl.com/examples/the-ordovician-silurian-extinction-a-turning-point-in-earths-history/

"The Ordovician-Silurian Extinction: A Turning Point in Earth's History," PapersOwl.com , 12-May-2024. [Online]. Available: https://papersowl.com/examples/the-ordovician-silurian-extinction-a-turning-point-in-earths-history/. [Accessed: 14-May-2024]

PapersOwl.com. (2024). The Ordovician-Silurian Extinction: A Turning Point in Earth's History . [Online]. Available at: https://papersowl.com/examples/the-ordovician-silurian-extinction-a-turning-point-in-earths-history/ [Accessed: 14-May-2024]

Don't let plagiarism ruin your grade

Hire a writer to get a unique paper crafted to your needs.

Our writers will help you fix any mistakes and get an A+!

Please check your inbox.

You can order an original essay written according to your instructions.

Trusted by over 1 million students worldwide

1. Tell Us Your Requirements

2. Pick your perfect writer

3. Get Your Paper and Pay

Hi! I'm Amy, your personal assistant!

Don't know where to start? Give me your paper requirements and I connect you to an academic expert.

short deadlines

100% Plagiarism-Free

Certified writers

• History Classics
• Your Profile
• Find History on Facebook (Opens in a new window)
• Find History on Twitter (Opens in a new window)
• Find History on YouTube (Opens in a new window)
• Find History on Instagram (Opens in a new window)
• Find History on TikTok (Opens in a new window)
• This Day In History
• History Podcasts
• History Vault

Earth Day 2024

By: History.com Editors

Updated: April 22, 2024 | Original: October 27, 2009

Earth Day was founded in 1970 as a day of education about environmental issues, and Earth Day 2024 is on Monday, April 22. The holiday is now a global celebration that’s sometimes extended into Earth Week, a full seven days of events focused on green living and confronting the climate crisis. The brainchild of Senator Gaylord Nelson and inspired by the protests of the 1960s, Earth Day began as a “national teach-in on the environment” and was held on April 22 to maximize the number of students that could be reached on university campuses. By raising public awareness of pollution, Nelson hoped to bring environmental causes into the national spotlight.

Earth Day History

By the early 1960s, Americans were becoming aware of the effects of pollution on the environment. Rachel Carson’s 1962 bestseller Silent Spring raised the specter of the dangerous effects of pesticides on the American countryside. Later in the decade, a 1969 fire on Cleveland’s Cuyahoga River shed light on the problem of chemical waste disposal. Until that time, protecting the planet’s natural resources was not part of the national political agenda, and the number of activists devoted to large-scale issues such as industrial pollution was minimal. Factories pumped pollutants into the air, lakes and rivers with few legal consequences. Big, gas-guzzling cars were considered a sign of prosperity. Only a small portion of the American population was familiar with–let alone practiced–recycling.

Did you know? A highlight of the United Nations' Earth Day celebration in New York City is the ringing of the Peace Bell, a gift from Japan, at the exact moment of the vernal equinox.

Who Started Earth Day?

Elected to the U.S. Senate in 1962, Senator Gaylord Nelson, a Democrat from Wisconsin, was determined to convince the federal government that the planet was at risk. In 1969, Nelson, considered one of the leaders of the modern environmental movement, developed the idea for Earth Day after being inspired by the anti- Vietnam War “teach-ins” that were taking place on college campuses around the United States. According to Nelson, he envisioned a large-scale, grassroots environmental demonstration “to shake up the political establishment and force this issue onto the national agenda.”

Nelson announced the Earth Day concept at a conference in Seattle in the fall of 1969 and invited the entire nation to get involved. He later recalled:

“The wire services carried the story from coast to coast. The response was electric. It took off like gangbusters. Telegrams, letters and telephone inquiries poured in from all across the country. The American people finally had a forum to express its concern about what was happening to the land, rivers, lakes and air—and they did so with spectacular exuberance.”

Denis Hayes, a young activist who had served as student president at Stanford University, was selected as Earth Day’s national coordinator, and he worked with an army of student volunteers and several staff members from Nelson’s Senate office to organize the project. According to Nelson, “Earth Day worked because of the spontaneous response at the grassroots level. We had neither the time nor resources to organize 20 million demonstrators and the thousands of schools and local communities that participated. That was the remarkable thing about Earth Day. It organized itself.”

On the first Earth Day on April 22, 1970, rallies were held in Philadelphia, Chicago , Los Angeles and most other American cities, according to the Environmental Protection Agency. In New York City , Mayor John Lindsay closed off a portion of Fifth Avenue to traffic for several hours and spoke at a rally in Union Square with actors Paul Newman and Ali McGraw. In Washington, D.C. , thousands of people listened to speeches and performances by singer Pete Seeger and others, and Congress went into recess so its members could speak to their constituents at Earth Day events.

The first Earth Day was effective at raising awareness about environmental issues and transforming public attitudes. According to the Environmental Protection Agency, “Public opinion polls indicate that a permanent change in national priorities followed Earth Day 1970. When polled in May 1971, 25 percent of the U.S. public declared protecting the environment to be an important goal, a 2,500 percent increase over 1969.” Earth Day kicked off the “Environmental decade with a bang,” as Senator Nelson later put it. During the 1970s, a number of important pieces of environmental legislation were passed, among them the Clean Air Act, the Water Quality Improvement Act, the Endangered Species Act, the Toxic Substances Control Act and the Surface Mining Control and Reclamation Act. Another key development was the establishment in December 1970 of the Environmental Protection Agency, which was tasked with protecting human health and safeguarding the natural environment—air, water and land.

What Do You Do For Earth Day?

Since 1970, Earth Day celebrations have grown. In 1990, Earth Day went global, with 200 million people in over 140 nations participating, according to the Earth Day Network (EDN), a nonprofit organization that coordinates Earth Day activities. In 2000, Earth Day focused on clean energy and involved hundreds of millions of people in 184 countries and 5,000 environmental groups, according to EDN. Activities ranged from a traveling, talking drum chain in Gabon, Africa, to a gathering of hundreds of thousands of people at the National Mall in Washington, D.C. 

Today, the Earth Day Network collaborates with more than 17,000 partners and organizations in 174 countries. According to EDN, more than 1 billion people are involved in Earth Day activities, making it “the largest secular civic event in the world.”

Sign up for Inside History

Get HISTORY’s most fascinating stories delivered to your inbox three times a week.

By submitting your information, you agree to receive emails from HISTORY and A+E Networks. You can opt out at any time. You must be 16 years or older and a resident of the United States.

More details : Privacy Notice | Terms of Use | Contact Us

An unexpected error occurred. Please try again.

Thank you for signing up

Our History

Every year on april 22, earth day marks the anniversary of the birth of the modern environmental movement in 1970. let’s take a look at the last half-century of mobilization for action:.

THE ORIGINS OF EARTH DAY

In the decades leading up to the first, americans were consuming vast amounts of leaded gas through massive and inefficient automobiles. industry belched out smoke and sludge with little fear of the consequences from either the law or bad press. air pollution was commonly accepted as the smell of prosperity. until this point, mainstream america remained largely oblivious to environmental concerns and how a polluted environment threatens human health., however, the stage was set for change with the publication of rachel carson’s new york times bestseller silent spring in 1962. the book represented a watershed moment, selling more than 500,000 copies in 24 countries as it raised public awareness and concern for living organisms, the environment and the inextricable links between pollution and public health., more on gaylord nelson and denis hayes, the idea for the first earth day, senator gaylord nelson, the junior senator from wisconsin, had long been concerned about the deteriorating environment in the united states. then in january 1969, he and many others witnessed the ravages of a massive oil spill in santa barbara, california. inspired by the student anti-war movement, senator nelson wanted to infuse the energy of student anti-war protests with an emerging public consciousness about air and water pollution. senator nelson announced the idea for a teach-in on college campuses to the national media, and persuaded pete mccloskey, a conservation-minded republican congressman, to serve as his co-chair..

Senator Gaylord Nelson recruited Denis Hayes, a young activist, to organize the campus teach-ins and to scale the idea to a broader public, and they choose April 22, a weekday falling between Spring Break and Final Exams, to maximize the greatest student participation.

Recognizing its potential to inspire all americans, hayes built a national staff of 85 to promote events across the land and the effort soon broadened to include a wide range of organizations, faith groups, and others.  they changed the name to earth day, which immediately sparked national media attention, and caught on across the country.  earth day inspired 20 million americans — at the time, 10% of the total population of the united states — to take to the streets, parks and auditoriums to demonstrate against the impacts of 150 years of industrial development which had left a growing legacy of serious human health impacts. .

Groups that had been fighting individually against oil spills, polluting factories and power plants, raw sewage, toxic dumps, pesticides, freeways, the loss of wilderness and the extinction of wildlife united on Earth Day around these shared common values. Earth Day 1970 achieved a rare political alignment, enlisting support from Republicans and Democrats, rich and poor, urban dwellers and farmers, business and labor leaders.

By the end of 1970, the first earth day led to the creation of the united states environmental protection agency and the passage of other first-of-their-kind environmental laws, including the national environmental education act, the occupational safety and health act, and the clean air act. two years later congress passed the clean water act., the dawn of the modern environmental movement. earth day 1970 became, and continues to be to this day, the largest secular day of protest in the world..

The principal Earth Day event in 1980, held in Washington. D.C. across from the White House, capped a decade of substantial US environmental legislation, including the Endangered Species Act, Marine Mammal Protection Act, Superfund, Toxics Substances Control Act, the Resource Conservation and Recovery Act, and of course the Clean Air Act and Clean Water Act. It had seen the creation of the Environmental Protection Agency and the banning of DDT and of lead in gasoline. Earth Day continued to expand internationally during the 80’s, as did international policy initiatives.

As 1990 approached, a group of environmental leaders approached denis hayes to once again organize another major campaign for the planet. this time, earth day went truly global, mobilizing 200 million people in 141 countries and lifting environmental issues onto the world stage. earth day 1990 gave a huge boost to recycling efforts worldwide and helped pave the way for the 1992 united nations earth summit in rio de janeiro. it also prompted president bill clinton to award senator nelson the presidential medal of freedom — the highest honor given to civilians in the united states — for his role as earth day founder..

As the millennium approached, Hayes agreed to spearhead another campaign, this time focusing on global warming and pushing for clean energy. Earth Day 2000 combined the big-picture feistiness of the first Earth Day with the international grassroots activism of Earth Day 1990. Earth Day had the internet to help link activists around the world. By the time April 22 came around, 5,000 environmental groups worldwide were on board, reaching out to hundreds of millions of people in a record 184 countries. Events varied: A talking drum chain traveled from village to village in Gabon, Africa, for example, while groups of thousands and more gathered worldwide for various events, rallies, and marches.

Nearly one billion people around the world took action for the 40th anniversary of earth day. an estimated 20,000 partners took action on climate change and other environmental issues through climate rallies, billion acts of green™, and by engaging civil leaders in plans to build a green economy, connected through the online action center at earthday.org. through the global day of conversation, more than 200 elected officials in more than 39 countries took part in active dialogues with their constituents about their efforts to create sustainable green economies and reduce their carbon footprints..

Signing of the Paris Agreement. It was no accident that the United Nations selected Earth Day to sign the most significant climate accord in the history of the climate and environmental movement. On Earth Day 2016, world leaders from 175 nations broke a record by doing exactly that.

Earth day 2020 was the 50th anniversary of earth day. activations included activities such as the great global cleanup, citizen science, advocacy, education, and street art. the year’s theme for earth day 2020 was “climate action.” due to the covid-19 pandemic, many of the planned activities were moved online. notably, earthday.org and a coalition of youth activists co-hosted earth day live, a three-day livestream commemorating the 50th anniversary of earth day in the united states. in total, over 1 billion people worldwide participated in earth day actions, and 100 million observed the 50th anniversary in what is being referred to as the largest online mass mobilization in history..

Earth Day Today

Earthday.org continues to build upon the work and legacy of its founders. joining with thousands of partners around the world, the organization continues to build a historic movement as citizens of the world rise up in a united call for the creativity, innovation, ambition, and bravery that we need to meet our climate crisis and seize the enormous opportunities of a zero-carbon future., join the movement.

By providing my phone number, I understand that Earth Day Network and its affiliates, service providers and non for profit partner organizations may use automated calling technologies and/or text message me on my cellular phone on a periodic basis. Earth Day Network will never charge for text message alerts. Carrier message and data rates may apply to such alerts. Text STOP to stop receiving messages.

Thank you for signing up!

Together we can #InvestInOurPlanet

Hi, It seems you are visiting us from India, would you like to visit our India pages?

Yes please No thank you

We will keep fighting for all libraries - stand with us!

Internet Archive Audio

• This Just In
• Grateful Dead
• Old Time Radio
• 78 RPMs and Cylinder Recordings
• Audio Books & Poetry
• Computers, Technology and Science
• Music, Arts & Culture
• News & Public Affairs
• Spirituality & Religion
• Radio News Archive

• Flickr Commons
• Occupy Wall Street Flickr
• NASA Images
• Solar System Collection
• Ames Research Center

• All Software
• Old School Emulation
• MS-DOS Games
• Historical Software
• Classic PC Games
• Software Library
• Kodi Archive and Support File
• Vintage Software
• CD-ROM Software
• CD-ROM Software Library
• Software Sites
• Tucows Software Library
• Shareware CD-ROMs
• Software Capsules Compilation
• CD-ROM Images
• ZX Spectrum
• DOOM Level CD

• Smithsonian Libraries
• FEDLINK (US)
• Lincoln Collection
• American Libraries
• Canadian Libraries
• Universal Library
• Project Gutenberg
• Children's Library
• Biodiversity Heritage Library
• Books by Language
• Additional Collections

• Prelinger Archives
• Democracy Now!
• Occupy Wall Street
• TV NSA Clip Library
• Animation & Cartoons
• Arts & Music
• Computers & Technology
• Cultural & Academic Films
• Ephemeral Films
• Sports Videos
• Videogame Videos
• Youth Media

Search the history of over 866 billion web pages on the Internet.

Mobile Apps

• Wayback Machine (iOS)
• Wayback Machine (Android)

Browser Extensions

Archive-it subscription.

• Explore the Collections
• Build Collections

Save Page Now

Capture a web page as it appears now for use as a trusted citation in the future.

Please enter a valid web address

• Donate Donate icon An illustration of a heart shape

An essay toward a natural history of the earth: and terrestrial bodies, especially minerals: as also of the sea, rivers, and springs. With an account of the universal deluge: and of the effects that it had upon the earth

Bookreader item preview, share or embed this item, flag this item for.

• Graphic Violence
• Explicit Sexual Content
• Hate Speech
• Misinformation/Disinformation
• Marketing/Phishing/Advertising
• Misleading/Inaccurate/Missing Metadata

This book is available with additional data at Biodiversity Heritage Library .

plus-circle Add Review comment Reviews

1,006 Views

3 Favorites

DOWNLOAD OPTIONS

In collections.

Uploaded by associate-daniel-euphrat on October 15, 2014

SIMILAR ITEMS (based on metadata)

History of Earth Day

Celebrate Earth Day with these tips for helping our environment.

Our planet is an amazing place, but it needs our help to thrive! That’s why each year on April 22, more than a billion people celebrate Earth Day to protect the planet from things like pollution and deforestation . By taking part in activities like picking up litter and planting trees, we’re making our world a happier, healthier place to live.

The first Earth Day was celebrated in 1970, when a United States senator from Wisconsin organized a national demonstration to raise awareness about environmental issues. Rallies took place across the country and, by the end of the year, the U.S. government had created the Environmental Protection Agency. By 1990, Earth Day was an event celebrated by more than 140 countries around the globe.

( Learn more at National Geographic .)

You can celebrate and protect the planet at the same time. Check out these Earth Day ideas to help save the planet any time of year.

BECOME A WASTE WARRIOR

The number of garbage trucks Americans fill each year would stretch halfway to the moon. Toilet paper tubes, made from cardboard, take two months to decompose in a landfill. A plastic bottle sticks around for way longer—it can take over 450 years to break down! But instead of turning to the trash bin, you could turn these items into an awesome telescope or a flower planter. Before you throw something away, think about whether it can be recycled or repurposed. You can also limit waste by reducing the amount of things you buy. For example, check the library for that book you have to read before visiting the store.

PLANT A TREE

Researchers estimate roughly 15 billion trees in the world are cut down each year, so help offset that loss by planting a tree of your own. Trees absorb carbon dioxide and release oxygen for people to breathe. They also provide shelter and food for animals such as squirrels and owls . Depending on where trees are planted, their shade can even reduce the need for air-conditioning in hotter months. How many more reasons do you need to go green?

TURN OFF THE LIGHTS

Does that lamp  really need to be on while the sun is out? Electricity doesn’t just happen—it has to be produced from things around us. A lot of times it comes from fossil fuels (such as coal, oil, or natural gas) that contribute to climate change . But electricity can also be made from renewable sources like wind, water, the sun, and even elephant dung! No matter where it’s coming from, try conserving electrical energy by using only what you need.

LIMIT YOUR WATER USAGE

It might seem like it’s everywhere, but clean, drinkable water is a limited resource. In fact less than one percent of the water on Earth can be used by humans. (The rest is either too salty or too difficult to access.) Turning off the faucet when you brush your teeth can conserve up to eight gallons of water a day. To help save even more water, challenge yourself to take a shorter shower (but still get clean!).

OFFER YOUR TIME

With a parent’s permission, volunteer to pick up trash at a nearby park, start a collection drive for recyclable items, or organize a screening of an environmentally themed movie. By getting involved and working with others, you’re not just helping the Earth—you’re making new friends too!

SPREAD THE MESSAGE

Talk to your friends and family members about what you’re doing and ask them to help. Need to get the conversation started? Get everyone together and reconnect with nature by taking one of our Get Outside challenges, or check out some other green tips you can share. The more people do, the better off our planet will be!

BE A PLANET HERO!

• In its lifetime, one reusable bag can prevent the use of 600 plastic bags.

• Recycling one can of soda will save enough energy to power a tv for three hours.

• Shutting down a computer when it's not in use cuts the energy consumption by 85 percent.

• For every mile walked instead of driven, nearly one pound of pollution is kept out of the air.

more to explore

Learn about plastic and how to reduce your use., save the earth, save the earth tips, endangered species act.

• Terms of Use
• Privacy Policy
• Your California Privacy Rights
• Children's Online Privacy Policy
• Interest-Based Ads
• About Nielsen Measurement
• Do Not Sell My Info
• National Geographic
• National Geographic Education
• Shop Nat Geo
• Customer Service
• Manage Your Subscription

Copyright © 1996-2015 National Geographic Society Copyright © 2015-2024 National Geographic Partners, LLC. All rights reserved

• Our Mission

Thich Nhat Hanh’s Walking Meditation

The late Thich Nhat Hanh emphasized the practice of mindful walking as a profound way to deepen our connection with our body and the earth. Read on and learn how to breathe, take a mindful step, and come back to your true home.

• Share on Facebook
• Email this Page

Many of us walk for the sole purpose of getting from one place to another. Now suppose we are walking to a sacred place. We would walk quietly and take each gentle step with reverence. I propose that we walk this way every time we walk on the earth. The earth is sacred and we touch her with each step. We should be very respectful, because we are walking on our mother. If we walk like that, then every step will be grounding, every step will be nourishing.

We can train ourselves to walk with reverence. Wherever we walk, whether it’s the railway station or the supermarket, we are walking on the earth and so we are in a holy sanctuary. If we remember to walk like that, we can be nourished and find solidity with each step.

To walk in this way, we have to notice each step. Each step made in mindfulness can bring us back to the here and the now. Go slowly. Mindfulness lights our way. We don’t rush. With each breath we may take just one step. We may have run all our life, but now we don’t have to run anymore. This is the time to stop running. To be grounded in the earth is to feel its solidity with each step and know that we are right where we are supposed to be.

Each mindful breath, each mindful step, reminds us that we are alive on this beautiful planet. We don’t need anything else. It is wonderful enough just to be alive, to breathe in, and to make one step. We have arrived at where real life is available—the present moment. If we breathe and walk in this way, we become as solid as a mountain.

There are those of us who have a comfortable house, but we don’t feel that we are at home. We don’t want for anything, and yet we don’t feel at home. All of us are looking for our solid ground, our true home. The earth is our true home and it is always there, beneath us and around us. Breathe, take a mindful step, and arrive. We are already at home.

Uniting Body and Mind

We can’t be grounded in our body if our mind is somewhere else. We each have a body that has been given us by the earth. This body is a wonder. In our daily lives, we may spend many hours forgetting the body. We get lost in our computer or in our worries, fear, or busyness. Walking meditation makes us whole again. Only when we are connected with our body are we truly alive. Healing is not possible without that connection. So walk and breathe in such a way that you can connect with your body deeply.

Walking meditation unites our body and our mind. We combine our breathing with our steps. When we breathe in, we may take two or three steps. When we breathe out, we may take three, four, or five steps. We pay attention to what is comfortable for our body.

Our breathing has the function of helping our body and mind to calm down. As we walk, we can say, Breathing in, I calm my body. Breathing out, I bring peace into my body. Calming the breath calms the body and reduces any pain and tension.

Walking meditation is first and foremost a practice to bring body and mind together peacefully.

When we walk like this, with our breath, we bring our body and our mind back together. Our body and our mind are two aspects of the same reality. If we remove our mind from our body, our body is dead. If we take our body out of our mind, our mind is dead. Don’t think that one can be if the other is not.

Walking meditation is first and foremost a practice to bring body and mind together peacefully. No matter what we do, the place to start is to calm down, because when our mind and our body have calmed down, we see more clearly. When we see our anger or sadness clearly, it dissipates. We begin to feel more compassion for ourselves and others. We can only feel this when body and mind are united.

Walking meditation should not be work. It is very pleasant, especially in the early morning when the air is still very fresh. When we walk mindfully, we see the beauty and the wonder of the earth around us, and we wake up. We see that we are living a very wonderful moment. If our mind is caught and preoccupied with our worries and suffering, we miss these things. We can value each step we take, and each step brings us happiness. When we look again at the earth and the sky, we see that the earth is a wonderful reality.

We Are Not Separate From the Earth

We think that the earth is the earth and we are something outside of the earth. But in fact we are inside of the earth. Imagine that the earth is the tree and we are a leaf. The earth is not the environment, something outside of us that we need to care for. The earth is us. Just as your parents, ancestors, and teachers are inside you, the earth is in you. Taking care of the earth, we take care of ourselves.

When we see that the earth is not just the environment, that the earth is in us, at that moment you can have real communion with the earth. But if we see the earth as only the environment, with ourselves in the center, then we only want to do something for the earth in order for us to survive. But that is not enough. That is a dualistic way of seeing.

We have to practice looking at our planet not just as matter, but as a living and sentient being. The universe, the sun, and the stars have contributed many elements to the earth, and when we look into the earth we see that it’s a very beautiful flower containing the presence of the whole universe. When we look into our own bodily formation, we are made of the same elements as the planet. It has made us. The earth and the universe are inside of us.

When we take mindful steps on the earth, our body and mind unite, and we unite with the earth. The earth gave birth to us and the earth will receive us again. Nothing is lost. Nothing is born. Nothing dies. We don’t need to wait until after our body has disintegrated to go back to Mother Earth. We are going back to Mother Earth at every moment. Whenever we breathe, whenever we step, we are returning to the earth. Even when we scratch ourselves, skin cells will fall and return to the earth.

Breathing in, I know Mother Earth is in me. Breathing out, I know Mother Earth is in me.

Earth includes the life sphere and the atmosphere. So you don’t have to wait until you die to go back to Mother Earth, because you are already in Mother Earth. We have to return to take refuge in our beautiful planet. I know that earth is my home. I don’t need to die in order to go back to Mother Earth. I am in Mother Earth right now, and Mother Earth is in me.

You may like to try this exercise while you walk: Breathing in, I know Mother Earth is in me. Breathing out, I know Mother Earth is in me.

Paul Tillich, the German theologian, said, “God is not a person but not less than a person.” This is true of the earth as well. It is more than a person. It has given birth to millions of species, including human beings. Many ancient cultures believed there was a deity that inhabited the sun, and they worshiped the sun. But when I do walking meditation and touching the earth, I do not have that kind of dualistic view. I am not worshiping the earth as a separate deity outside of myself.

I think of the earth as a bodhisattva, a great and compassionate being. A bodhisattva is a being who has awakening, understanding, and love. Any living being who has awakening, peace, understanding, and love can be called a bodhisattva, but a bodhisattva doesn’t have to be a human being. When we look into a tree, we see the tree is fresh, it nourishes life, and it offers shade and beauty. It’s a place of refuge for so many birds and other creatures. A bodhisattva is not something that is up in the clouds far away from us. Bodhisattvas are all around us. A young person who has love, who has freshness, who has understanding, who offers us a lot of happiness, is a bodhisattva. The pine standing in the garden gives us joy, offers us oxygen, and makes life more beautiful.

When we say that earth is a beautiful bodhisattva, this is not our imagination. It is a fact that the earth is giving life and she is very beautiful. The bodhisattva is not a separate spirit inhabiting the earth; we should transcend that idea. There are not two separate things—the earth, which is a material thing, and the spirit of the earth, a nonmaterial thing that inhabits the earth.

Our planet earth is itself a true, great bodhisattva. It embodies so many great virtues. The earth is solid—it can carry so many things. It is patient—it takes its time moving glaciers and carving rocks. The earth doesn’t discriminate. We can throw fragrant flowers on the earth, or we can throw urine and excrement on the earth, and the earth purifies it. The earth has a great capacity to endure, and it offers so much to nourish us—water, shelter, food, and air to breathe.

When we recognize the virtues, the talent, the beauty of the earth bodhisattva, love is born. You love the earth and the earth loves you. You would do anything for the well-being of the earth. And the earth will do anything for your well-being. That is the natural outcome of the real loving relationship. The earth is not just your environment, to be taken care of or worshiped; you are each other. Every mindful step can manifest that love.

With each step the earth heals us, and with each step we heal the earth.

Part of love is responsibility. In Buddhism, we speak of meditation as an act of awakening. To awaken is to be awake to something. We need to be awake to the fact that the earth is in danger and living species on earth are also in danger. When we walk mindfully, each step reminds us of our responsibility. We have to protect the earth with the same commitment we have to protect our family and ourselves. The earth can nourish and heal us but it suffers as well. With each step the earth heals us, and with each step we heal the earth.

When we walk mindfully on the face of the earth, we are grounded in her generosity and we cannot help but be grateful. All of the earth’s qualities of patience, stability, creativity, love, and nondiscrimination are available to us when we walk reverently, aware of our connection.

Let the Buddha Walk

I have a student named Sister Tri Hai who spent a long time in prison. She was a peace activist I knew since she was in middle school. She came to the United States to study English literature before going back to Vietnam and becoming a nun. When she was out in the streets advocating for peaceful change, she was arrested and put in prison.

During the day, the prison guards didn’t like her to sit in meditation. When they see someone sitting in a prison cell solidly and stably, it feels a bit threatening. So she waited until the lights had gone out, and she would sit like a person who has freedom. In outer appearance she was caught in the prison. But inside she was completely free. When you sit like that, the walls are not there. You’re in touch with the whole universe. You have more freedom than people outside who are imprisoning themselves in their agitation.

Sister Tri Hai also practiced walking meditation in her prison cell. It was very small—after seven steps she had to turn around and come back. Sitting and walking mindfully gave her space inside. She taught other prisoners in her cell how to sit and how to breathe so they would suffer less. They were in a cold cell, but through their walking meditation, they were grounded in the solid beauty of the earth.

Those of us who can walk on the earth, who can walk in freedom, should do it. If we rush from one place to another, without practicing walking meditation, it is such a waste. What is walking for? Walking is for nothing. It’s just for walking. That is our ultimate aim—walking in the spring breeze. We have to walk so that we have happiness, so that we can be a free person. We have to let go of everything, and not seek or long or search for anything. There is enough for us to be happy.

All the Buddhist stories tell us that the Buddha had a lot of happiness when he sat, when he walked, when he ate. We have some experience of this. We know there are moments when we’re walking or sitting that we are so happy. We also know that there are times, because of illness or physical disability or because our mind is caught elsewhere, when we cannot walk freely like the Buddha. There are those of us who do not have the use of our legs. There are those of us who are in prison, like Sister Tri Hai, and only have a few feet of space. But we can all invite the Buddha to walk for us. When we have difficulty, we can leave that difficulty behind and let the Buddha walk for us. In a while the solidity of the earth can help us return to ourselves.

If we sit mindfully, if we walk mindfully and reverently on the earth, we will generate the energies of mindfulness, of peace, and of compassion in both body and mind.

We are made of body and mind. Our body can radiate the energy of peace and compassion. Our mind also has energy. The energy of the mind can be powerful. If the energy of the mind is filled with fear and anger, it can be very destructive. But if we sit mindfully, if we walk mindfully and reverently on the earth, we will generate the energies of mindfulness, of peace, and of compassion in both body and mind. This kind of energy can heal and transform.

If you walk reverently on the earth with two other people, soaking in the earth’s solidity, you will all three radiate and benefit from the energy of peace and compassion. If three hundred people sit or walk like this, each one generates the energy of mindfulness, peace, and compassion, and everyone in the group receives that healing energy. The energy of peace and mindfulness does not come from elsewhere. It comes from us. It comes from our capacity to breathe, to walk, to sit mindfully and recognize the wonders of life.

When you walk reverently and solidly on this earth and I do the same, we send out waves of compassion and peace. It is this compassion that will heal ourselves, each other, and this beautiful green earth.

Meditation: Walking on the Earth

Walk slowly, in a relaxed way. When you practice this way, your steps are those of the most secure person on earth. Feel the gravity that makes every step attach to the earth. With each step, you are grounded on the earth.

One way to practice walking meditation is to breathe in and take one step, and focus all your attention on the sole of your foot. If you have not arrived fully, 100 percent in the here and the now, don’t take the next step. I’m sure you can take a step like that because there is buddhanature in you. Buddhanature is the capacity of being aware of what is going on. It is what allows you to recognize what you are doing in the current moment and to say to yourself, I am alive, I am taking a step. Anyone can do this. There is a buddha in every one of us, and we should allow the buddha to walk.

While walking, practice conscious breathing by counting steps. Notice each breath and the number of steps you take as you breathe in and as you breathe out. Don’t try to control your breathing. Allow your lungs as much time and air as they need, and simply notice how many steps you take as your lungs fill up and how many you take as they empty, mindful of both your breath and your steps. The link is the counting.

When you walk uphill or downhill, the number of steps per breath will change. Always follow the needs of your lungs. You may notice that your exhalation is longer than your inhalation. You might find that you take three steps during your in-breath and four steps during your out-breath, or two steps, then three steps. If this is comfortable for you, please enjoy practicing this way. You can also try making the in-breath and the out-breath the same length, so that you take three steps with your in-breath and three with your out-breath. Keep walking and you will find the natural connection between your breath and your steps.

Don’t forget to practice smiling. Your half-smile will bring calm and delight to your steps and your breath, and help sustain your attention. After practicing for half an hour or an hour, you will find that your breath, your steps, your counting, and your half-smile all blend together in a marvelous balance of mindfulness. Each step grounds us in the solidity of the earth. With each step we fully arrive in the present moment.

Walking Meditation Poem

I take refuge in Mother Earth. Every breath, every step manifests our love. Every breath brings happiness. Every step brings happiness. I see the whole cosmos in the earth.

Thich Nhat Hanh