The Geological Evolution of the Earth

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The Geological Evolution of the Earth

This document presents in a vertical time line images of the Earth's geologic evolution from 510 million years ago to the present -- roughly the last 10% of the Earth's existence. The crust has already solidified and the atmosphere has accumulated oxygen from 300 million years of algal growth in the Earth's vast oceans.

 

The continental events of the period covered here form three very large scale episodes: [1] the break up of the ancient south polar supercontinent of Rodinia, [2] the reassembly of Rodinian fragments (Gondwana and Laurasia) into the pole-to-pole supercontinent of Pangaea, and [3] the fragmentation and reassembly of Pangaea into the continental pattern of today.

 

These geologic transformations are illustrated in hemispheric views approximately centered on the North American and northern European (Baltic) continental blocks. They are adapted from exhibits at the fine plate tectonics site assembled by Dr. Ron Blakey of the University of Arizona. These are in turn based principally on data from: Cook and Bally, Stratigraphic Atlas of North and Central America, Princeton University Press (1975); Scotese and Glonka, Paleomap, University of Texas at Arlington (1992); and Ziegler, Evolution of the Arctic-North Atlantic and the Western Tethys, AAPG Memoir 43 (1988).

 

The images illustrating terrestrial life in the various geologic eras draw on exhibits linked from the online U.C. Berkeley Museum of Paleontology, which also offers several animated images of plate tectonics.

 

START THE TIMELINE

 

 

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In the late Cambrian, continental blocks comprising about one third of the supercontinent Rodinia, which extended from the South Pole to the equator, broke away and drifted north and west. These blocks included ancestral parts of North America or Laurentia [NA in the image], northern Europe or Baltica , Siberia , and central Asia (extreme upper right edge of globe). Each continental block carried with it a broad and shallow coastal shelf where Cambrian marine life thrived.

 

The ancestral North American continent stretched across the Cambrian equator, turned clockwise nearly 90° from its modern orientation (today's east coast lay along the south). An arc [ocean mountain range] and ocean trench, the ancestral American east coast, approached from the south, while ancestral northern Europe [baltica B] and Central Asia [siberia S] drifted upwards from the southeast.

 

Not seen in this image are the massive remains of Rodinia -- including South America, Africa, Australia, Antarctica, two blocks comprising modern China, and blocks forming Southeastern Asia, India and the Middle East.

 

With one exception (the phylum Bryozoa), every metazoan phylum with hard parts, and many that lack hard parts, make their first appearances in the Cambrian. However, Cambrian marine life was quite different from modern life forms; the dominant invertebrates with hard parts were trilobites, inarticulate brachiopods, archaeocyathids, and problematic conical fossils known as hyolithids. Many Early Cambrian invertebrates are known only from "small shelly fossils" -- tiny plates and scales and spines and tubes and so on, many of which were pieces of the skeletons of larger animals.

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In the Ordovician era, Baltica and Siberia continued their drift toward North America, creating a loose collection of large land masses separated by shallow coastal seas. The central Asian block continued to drift toward the North Pole. Rotating slightly as a result of these approaching land masses, much of eastern North America (today's western Canada and United States) lay submerged as a very large coastal shelf (white in the image).

 

The Caledonian orogeny [mountain range] built up from the pressure between Siberia and the eastern edge of North America (modern Greenland). Further south, the long Taconic orogeny resulted from the approach of Baltica. Both the Avalonian arc, stretching east-west in the Iapetus Ocean (south of the North American plate), and the Taconic orogeny along the ancestral Appalachian Mountains in North America were areas of extensive volcanic activity.

 

The large blocks that will become modern Tibet and China appear at the far right edge of the globe. The remnants of Rodinia (now called Gondwana), remained on the other side of the globe, stretching from the South Pole to the equator, with South America and Africa upside down from their current position and closest to the South Pole.

 

The Ordovician is best known for the presence of its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More recently, tetrahedral spores similar to those of primitive land plants have been found, suggesting that plants invaded land at this time.

 

From the Early to Middle Ordovician, the earth experienced a milder, warmer and more humid climate. However, massive glaciers formed when Gondwana moved over the South Pole during the Late Ordovician, causing shallow seas to drain and sea levels to drop. These climate shifts likely caused the mass extinctions that characterize the end of the Ordovician, in which 60% of all marine invertebrate genera and 25% of all biological families went extinct.

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During the Silurian era, the continents of North America, Baltica and Siberia reassembled into the supercontinent of Laurasia [the Old Red continent]. This process raised new mountain ranges in the Caledonian orogeny along the impact edges of the Siberian and North American continental blocks. The Avalonian arc moved very close to Laurentia, working with the colliding Baltic [northern European, E] block to raise the Taconic orogeny further.

 

Ancestral Greenland, northern Europe and the eastern United States remained above sea level, while most of the areas that are today western Canada, Russia and the United States were submerged.

 

During this period Gondwana, made up of the fused continents South America, Africa, Antarctica, India and Australia, slowly circled around the globe toward Laurasia from the south and east. Land fragments comprising modern Iberia, western Europe and the Balkans rifted from its southern edge, and these (bottom of globe) moved into the Iapetus Ocean along the southern edge of North America.

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In the Devonian era the consolidation of Laurasia was completed. The large Caledonian-Acadian orogeny resulted from the continued collision of the three continental blocks, but most of what is today central Europe and the United States were submerged under shallow coastal seas. Siberia began to rotate and move north, separating it from the northern European block [E], and creating mountain ranges along modern Greenland in the process.

 

Several large blocks (later to comprise China and Tibet, visible on the far right of the globe) broke away from the north (equatorial) end of Gondwana [GO], while the bulk of this supercontinent -- containing all of ancestral Africa, South America, Antarctica, Australia and India -- began to move over the South Pole and up the opposite side of the globe, toward Laurasia positioned on the Earth's equator. The Prototethys and Rheic Oceans formed in the narrowing gap, which included the ancestral Iberian Peninsula as a large island.

 

As Gondwana moved upward, it pushed the eastern edge of Laurasia against the Pacific plate [Panthalassa Ocean], forming a volcanic arc at the boundary between the North American and Pacific plates along the North America's west (today's southwest) coast. This arc persisted to this day as the eastern edge of the Pacific "ring of fire" -- the earthquake faults and active volcanos along the western North American coast.

 

By the start of the Devonian, the first major radiations of terrestrial (vascular) plants had already taken place, though the vegetation of the early Devonian consisted primarily of small plants up to a meter tall. By the end of the Devonian, ferns, horsetails and seed plants had also appeared, producing the first trees and forests. Also during the Devonian, two major animal groups colonized the land: the first tetrapods or land-living vertebrates, and the first terrestrial arthropods, including wingless insects and spiders. In the Devonian oceans, brachiopods, crinoids and other echinoderms flourished, and tabulate and rugose corals, and ammonites were also common. Many new kinds of fish appeared.

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In the Carboniferous era (the Mississipian is shown here), the Antler arc continued its collision with western North America, creating a widely curving pair of ocean trenches with the Antler orogeny (the ancestral central Rocky Mountains) between them. Most of today's central and south United States remained submerged as a coastal shelf, whose shallow waters laid down the limestone deposits that were later hollowed into the many caves of the American south and southwest.

 

Siberia broke away from Laurasia and drifted northwards, trailing remnants of the Caledonian orogeny in its wake. The remnant blocks of Tibet and China (far right of the globe) remained roughly stationary, while the central Asian block drifted south from the North Pole towards them.

 

Meanwhile Gondwana collided with Laurasia from the south, leading with the continental areas later to become South America [sA] and Africa [AF]. This collision created the Variscan orogeny, rising over the area of today's western Europe and Iberian peninsula, wedged between Laurasia and the advancing northern edge of Africa.

 

The Carboniferous era saw the first amphibians and the climax of large ancient fern forests, which built up over millions of years the coal and petrochemical deposits that fueled the Twentieth Century. Gondwana was covered by a massive polar sheet of ice with many glaciers extending northwards.

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During the Permian era the newly assembled supercontinent of Pangaea ("All Earth") lay across the equator stretching almost from pole to pole. The former Laurasia to the north [E and S] and the African continental block to the south [AF] formed the Tethys Ocean, which opened to the east. Most of the rest of the surface area of the Earth was occupied by a single sea, the Panthalassa Ocean (ancestral Pacific Ocean).

 

As Gondwana collided with Laurasia, it pushed the North American continent northward off the equator (partly submerging the ancestral Rocky Mountains), and carried the northern European continent upwards into Siberia again, creating the Ural orogeny. The Appalachian, Ouachita, Marathon, Ural, Variscan, and Hercynian orogenies that resulted from this massive continental reassembly created some of the largest mountains and longest continuous mountain ranges of all time.

 

Though this mountain-building slowed Gondwana's northward movement, the momentum broke several large blocks from its northeastern edge. These drifted into the Tethys Ocean toward Siberia, ploughing an ocean trench as they moved. Most notable were the Cimmerian blocks -- which probably formed a single long finger of land, just visible (white) at the righthand edge of the globe -- that included today's Turkey, Iran, and Afghanistan.

 

The vast interior regions of this Pangaea were probably dry, with great seasonal fluctuations due to the lack of any moderating effect from nearby bodies of water. Only mountains and coastal areas received rainfall throughout the year. There are indications that glaciation decreased and sea levels rose.

 

The Permian period saw the largest mass extinction in the history of life on Earth. It affected many groups of organisms in many different environments, but marine communities the most by far, causing the extinction of most of the shallow water marine invertebrates of the time and clearing the way for other groups of sea life. On land, a relatively smaller extinction of diapsids and synapsids led to the start of the "Age of Dinosaurs." Great forests of fern-like plants gave way to gymnosperms (seed bearing plants), including modern conifers, while the Permian oceans saw proliferation of corals, sponges and early fishes.

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During the Triassic era the residual northward momentum of Gondwana pushed Siberia to the North Pole. As Siberia moved northward it created a new ocean trench, the ancestral eastern edge of the "ring of fire" circling the Pacific plate. From here it began to pivot south, toward the scattered Asian blocks along its southern edge, which created a long "tail" or peninsula (ancestral Southeast Asia) extending south from Siberia.

 

The redistributing continental plates also lifted the shallow continental seas bordering Laurasia, and more of North America rose as dry land.

 

The Pacific plate collision with the long eastern coast of Pangaea created a north-south arc reaching almost from pole to pole. Contributing to this arc, the continued pressure on the southwestern edge of North America formed the Sonoman orogeny, the ancestral Mexican plateau. The western mountains also extended northward, lifting ancestral Alaska from the sea.

 

The Tethys Ocean expanded considerably, and Cimmeria (Turkey, Iran, and Afghanistan, white area at right of globe) continued to drift northward towards Laurasia.

 

As it fused as a single large land mass, Pangaea brought into contact many families of dinosaurs and plants that had flourished in separate ecologies. Crucially, it exposed these groups to new groups of viruses and bacteria, probably causing many of the Triassic extinctions in larger animals that opened ecological niches for the rise of dinosaurs.

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During the Jurassic era, as the Cimmerian blocks collided with the Siberian extension of Pangaea in the northeast, the various components of the supercontinent began to shift and rotate. These movements formed rifts between the continental components of Pangaea, and began the 100 million-year-long process of continental redistribution that continued through the end of the Cretaceous period (70 million years ago).

 

The first major rift was a southwestward tear from ancestral Mexico to the Tethys Ocean -- along the ancient join of Laurasia and Gondwana, but leaving the Avalonian blocks (ancestral Florida and Piedmont) attached to North America along the Appalachian suture. This rift formed the ancestral Gulf of Mexico and shortly thereafter the ancestral North Atlantic Ocean.

 

The pressure of North America against the Pacific plate extended the Rocky Mountains northward into today's Canada and Alaska. This Cordilleran arc was now firmly established along the Pacific margin of North America.

 

In Asia, a clockwise (southward) movement of Laurasia (Baltica and Siberia) caused complex patterns of subsidence and uplift across the European-Siberia land mass. Asia became isolated from Europe, and Europe became a scattered field of large islands; the ancestral blocks of Italy and the Balkans drifted further into the narrowing Tethys Ocean between Africa and Laurasia. The impact of Cimmeria with Laurasia formed the Cimmerian orogeny, including the ancestral Caucasus Mountains, and the impact of the Chinese and Tibetan blocks raised the ancestral Siberian and Chinese mountains.

 

At the lower right edge of the globe, ancestral India can be seen breaking away from the eastern edge of Africa [AF]. Unseen on the other side of the globe are the continent of Australia (which lies at the other end of a single continental plate shared with India) and Antarctica, near the South Pole.

 

During the Jurassic, vertebrate life evolved its largest and most unusual species. Great plant-eating dinosaurs (among the largest animals that ever lived) fed on lush growths of ferns and palm-like cycads and bennettitaleans. Smaller but highly effective carnivores stalked these giant herbivores -- and each other. The oceans teemed with fish, squid, coiled ammonites, great ichthyosaurs and long-necked plesiosaurs. Vertebrates took to the air (the pterosaurs and earliest birds), and the first mammals appeared.

 

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During the early Cretaceous era continental fragmentation and reassembly continued. The Atlantic expanded as North America drifted north and east, away from Africa, which began to detach from South America. Antarctica and the India-Australia plate detached from the east coast of Africa, drifting north and east toward Asia.

 

In Asia, blocks comprising today's Tibet and China fused with the southern edge of Siberia, raising the Chinese-Tibetan mountain ranges. Blocks ancestral to the Himalaya Mountains, Southeastern Asia and Maylasia remained scattered as a vast archipelago to the south.

 

The Ural Mountains began to rise again as Baltica detached from Greenland. Most of Europe subsided into a loose collection of large islands. The Iberian peninsula, Italy and Greece approached Europe from the south. Much of central Europe, northern Africa and the Middle East remained submerged as shallow seas.

 

The Pacific plate continued to ride the western edge of North America and the Sevier orogeny (southwestern Rocky Mountains) began. The Cordilleran arc became completely isolated from eastern North America by the Inland Sea. As a result, dinosaur species in eastern North America evolved differently from those in the west, which in turn (as the Cordilleran arc joined Siberia across the ancestral Bering Strait) were common with those in Asia. Greenland began to detach from North America.

 

On the other side of the globe, India drifted away from Africa as Antarctica centered on the South Pole. Australia separated from Antarctica and pivoted northward into the southern edge of the Pacific plate.

 

During the Cretaceous life as it now exists on Earth came together. Though it marks the end of the "Age of Dinosaurs," new kinds of dinosaurs appeared even then -- including the first of birds (in Australia), and the first ceratopsians and pachycepalosaurids. In addition, the first fossils of many insect groups, modern mammals, and the first flowering plants appeared at this time. These reflect the increased regional differences in floras and faunas that evolved after Pangaea broke into separate lands.

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During the Late Cretaceous era continental fragmentation reached its peak and the process of continental reassembly began. In particular, the buildup of mountains in southern Laurasia continued from the gradual consolidation of many Asian land blocks.

 

Africa, North America and South America drifted further apart: Africa toward Europe, North America toward the North Pole and Siberia. These drifts enlarged the southern Atlantic Ocean and the Gulf of Mexico, added the Colorado Laramide orogeny to the Sevier orogeny (central Rocky Mountains), and formed the Caribbean arc.

 

Large portions of all the continents remained submerged under shallow coastal seas. The Cordilleran arc, no longer connected to Asia, remained separated from eastern North America by the Inland Sea. The fragmentation of Europe into many large islands reached its peak, and Europe continued isolated from Asia. Greenland drifted farther from North America. Much of northern Africa, the ancestral Middle East, the Indian subcontinent and northeastern South America were submerged under shallow coastal seas.

 

India and Australia continued to move northward towards Eurasia, opening the Indian Ocean and beginning to close the Tethys Ocean. As India separated from the southeast coast of Africa it pulled Madagascar in its wake.

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During the Cenozoic era (the Eocene is shown here), continental reassembly continued, and the modern patterns of Earth finally appeared.

 

The northward momentum of North America into Siberia around the deepening Artic Ocean, pushed the Alaskan and Canadian rockies to their maximum height and extent. The Servier orogeny continued southward to link with South America, and the Caribbean arc uncoiled northward.

 

In Europe, the northward movement of Africa consolidated many southern European land fragments to create the Pyrenees, the Iberian plateau, the Alps, the Balkans, and the northern African Atlas Mountains around the margins of the emerging Mediterranean Sea. As these mountain building forces slowed the northward movement of Africa, the drift momentum detached the Saudi-Arabian Peninsula from its northeastern edge.

 

On the other side of the globe, India began its powerful collision with Eurasia from the south, shepherding northward the many remnant Asian blocks that became Iran, Afghanistan, central Asia, Tibet, China and Southeast Asia, and compressing into Siberia and raising further the Himalayan Mountains. During the Miocene and Holocene, Australia, moving north with India, met with fragments of Southeastern Asia moving south, forming by stages the volcanic island complexes of the Philippines, Borneo, the Indonesian archipelago, New Guinea and the volcanic southern Pacific Island chains. Antarctica rotated around the South pole.

 

The Cenozoic spans about 65 million years, from the extinction of non-avian dinosaurs to the present. The Cenozoic is sometimes called the Age of Mammals, because the largest Cenozoic land animals were herbivorous and carnivorous mammals and birds, though the diversity of life during the Cenozoic includes many new species of fishes, flowering plants and insects.

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Today's Earth continues the process of continental reassembly.

The movement northward of India and Australia continues to raise the Himalaya Mountains and spark many volcanos in Southeast Asian islands and archipelagos. The subduction of the Pacific plate under the North American continent has slowed somewhat, though earthquakes and volcanic eruptions still occur. The Atlantic continues to widen as Africa and Europe drift farther from North and South America.

What does the future hold? The current direction of plate movements suggests that Africa will drive into Europe, rotating clockwise and closing the Mediterranean Sea; South America will drift northward, toward Florida, until all of Brazil is north of the equator; the Bering Strait will close and drift far south; and the Arctic Sea will narrow and shift southward into the edge of the Pacific plate. This implies that volcanic activity around the Pacific rim may move northward, and both Alaska and Siberia will lie below the Arctic circle. India and Australia will likely remain in approximately their present positions, and Antarctica may drift away from the pole in the wake of South America.

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last revised 11.26.01 • © 2001 handprint

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