- Geological history of Earth
, impacting the Earth in a glancing blow. [cite journal | last = R. Canup and E. Asphaug | title = Origin of the Moon in a giant impact near the end of the Earth's formation | journal = Nature | volume = 412 | pages = 708–712 | date = 2001 | url = http://www.nature.com/nature/journal/v412/n6848/abs/412708a0.html | doi = 10.1038/35089010 ] Some of this object's mass merged with the Earth and a portion was ejected into space, but enough material survived to form an orbiting moon. Outgassing and volcanic activity produced the primordial atmosphere. Condensing
water vapor, augmented by ice delivered by comets, produced the oceans. [cite journal | author=Morbidelli, A.; Chambers, J.; Lunine, J. I.; Petit, J. M.; Robert, F.; Valsecchi, G. B.; Cyr, K. E. | title=Source regions and time scales for the delivery of water to Earth | journal=Meteoritics & Planetary Science | year=2000 | volume=35 | issue=6 | pages=1309–1320 | url=http://adsabs.harvard.edu/abs/2000M&PS...35.1309M | accessdate=2007-03-06 ] As the surface continually reshaped itself, over hundreds of millions of years, continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 Ma (million years ago) (ICS 2004), the earliest known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 Ma (ICS 2004), then finally Pangaea, which broke apart 180 Ma (ICS 2004). [cite journal | author=Murphy, J. B.; Nance, R. D. | title=How do supercontinents assemble? | journal=American Scientist | year=1965 | volume=92 | pages=324–33 | url=http://scienceweek.com/2004/sa040730-5.htm | accessdate=2007-03-05 | doi=10.1511/2004.4.324 ] The present pattern of ice ages began about 40 Ma (ICS 2004), then intensified during the Pleistoceneabout 3 Ma (ICS 2004). The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40,000–100,000 years. The last glacial periodof the current ice age ended about 10,000 years ago. [cite web | author=Staff | url = http://www.lakepowell.net/sciencecenter/paleoclimate.htm | title = Paleoclimatology - The Study of Ancient Climates | publisher = Page Paleontology Science Center | accessdate = 2007-03-02 ]
The geological history of the
Earthcan be broadly classified into two periods: the Precambriansupereon and the Phanerozoiceon.
Precambrian includes approximately 90% of geologic time. It extends from 4.6 billion years ago to the beginning of the Cambrian Period (about 570 Ma). It includes 3 eons namely:
Hadeantime (4.6 - 3.8 bya), the Solar Systemwas forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The Hadean Eon isn't formally recognized, but it essentially marks the era before there were any rocks. The oldest dated zircons date from about 4400 Ma (ICS 2004) [ [http://www.nature.com/nature/journal/v409/n6817/abs/409175A0.html Wilde, S. A.; Valley, J.W.; Peck, W.H. and Graham, C.M. (2001) "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago" "Nature" 409: pp. 175-178] Abstract] - very close to the hypothesized time of the Earth's formation.
During the Hadean period the
Late Heavy Bombardmentoccurred (approximately 3800 to 4100 Ma) during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well.
The Earth of the early
Archean(3.8-2.5 bya) may have had a different tectonic style. During this time, the Earth's crust cooled enough that rocks and continental plates began to form. Some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today, resulting in a much greater rate of recycling of crustal material. This may have prevented cratonisation and continent formation until the mantle cooled and convection slowed down. Others argue that the sub continental lithospheric mantle is too buoyant to subduct and that the lack of Archean rocks is a function of erosionand subsequent tectonicevents.
In contrast to the
Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments, and banded iron formations. Carbonaterocks are rare, indicating that the oceans were more acidic due to dissolved carbon dioxidethan during the Proterozoic. [John D. Cooper, Richard H. Miller, and Jacqueline Patterson, "A Trip Through Time: Principles of Historical Geology", (Columbus: Merrill Publishing Company, 1986), p. 180.] Greenstone belts are typical Archean formations, consisting of alternating high and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island arcs and deposited in a forearc basin. In short, greenstone belts represent sutured protocontinents. [Stanley, pp. 302-3]
The geologic record of the Proterozoic (2.5-0.57 bya) is much better than that for the preceding
Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of these rocks are less metamorphosed than Archean-age ones, and plenty are unaltered. [cite book| last=Stanley| first=Steven M.| title=Earth System History| location=New York| publisher=W.H. Freeman and Company| year=1999| id=ISBN 0-7167-2882-6 | pages= 315] Study of these rocks show that the eon featured massive, rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and wholly-modern orogenic activity. [Stanley, 315-18, 329-32]
The first known glaciations occurred during the Proterozoic, one began shortly after the beginning of the eon, while there were at least four during the Neoproterozoic, climaxing with the
Snowball Earthof the Varangian glaciation. [Stanley, 320-1, 325]
The Phanerozoic Eon is the current eon in the geologic timescale. It covers roughly 545 million years. During the period covered, continents drifted about, eventually collected into a single landmass known as
Pangeaand then split up into the current continental landmasses.The Phanerozoic is divided into three eras — the Paleozoic, the Mesozoic, and the Cenozoic.
The Paleozoic spanned from roughly 542 Ma (ICS 2004) to roughly 251 Ma (ICS 2004), and is subdivided into six geologic periods; from oldest to youngest they are: the
Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Geologically, the Paleozoicstarts shortly after the breakup of a supercontinent called Pannotiaand at the end of a global ice age. Throughout the early Palaeozoic, the Earth's landmass was broken up into a substantial number of relatively small continents. Toward the end of the era, the continents gathered together into a supercontinent called Pangaea, which included most of the Earth's land area.
The Cambrian is a major division of the
geologic timescalethat begins about 542 ± 1.0 Ma (ICS 2004). Cambriancontinents are thought to have resulted from the breakup of a Neoproterozoicsupercontinent called Pannotia. The waters of the Cambrian period appear to have been widespread and shallow. Continental drift rates may have been anomalously high. Laurentia, Balticaand Siberiaremained independent continents following the break-up of the supercontinent of Pannotia. Gondwanastarted to drift towards the South Pole. Panthalassacovered most of the southern hemisphere, and minor oceans included the Proto-Tethys Ocean, Iapetus Ocean, and Khanty Ocean.
The Ordovician period started at a major extinction event called the
Cambrian-Ordovician extinction eventssome time about 488.3 ± 1.7 Ma (ICS 2004). During the Ordovician, the southern continents were collected into a single continent called Gondwana. Gondwana started the period in the equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician, the continents Laurentia, Siberia, and Baltica were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Balticabegan to move towards Laurentia later in the period, causing the Iapetus Ocean to shrink between them. Also, Avaloniabroke free from Gondwana and began to head north towards Laurentia. The Rheic Oceanwas formed as a result of this. By the end of the period, Gondwana had neared or approached the pole and was largely glaciated.
The Ordovician came to a close in a series of
extinction events that, taken together, comprise the second largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct. The only larger one was the Permian-Triassic extinction event. The extinctions occurred approximately 444-447 Ma (ICS 2004) and mark the boundary between the Ordovician and the following SilurianPeriod.The most commonly accepted theory is that these events were triggered by the onset of an ice age, in the Hirnantian faunal stage that ended the long, stable greenhouseconditions typical of the Ordovician. The ice age was probably not as long-lasting as once thought; study of oxygen isotopesin fossil brachiopods shows that it was probably no longer than 0.5 to 1.5 million years. [Steven M. Stanley, "Earth System History", (New York: W.H. Freeman and Company, 1999), 358.] The event was preceded by a fall in atmospheric carbon dioxide (from 7000ppm to 4400ppm) which selectively affected the shallow seas where most organisms lived. As the southern supercontinent Gondwanadrifted over the South Pole, ice caps formed on it, which have been detected in Upper Ordovician rock strata of North Africaand then-adjacent northeastern South America, which were south-polar locations at the time.
The Silurian is a major division of the
geologic timescalethat started about 443.7 ± 1.5 Ma (ICS 2004). During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late Ordovician glaciation. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. Other cratons and continent fragments drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. The vast ocean of Panthalassa covered most of the northern hemisphere. Other minor oceans include, Proto-Tethys, Paleo-Tethys, Rheic Ocean, a seaway of Iapetus Ocean (now in between Avalonia and Laurentia), and newly formed Ural Ocean.
The Devonian spanned roughly from 416 to 359 Ma (ICS 2004). The period was a time of great tectonic activity, as
Laurasiaand Gondwanaland drew closer together. The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn. In these near-deserts, the Old Red Sandstonesedimentary beds formed, made red by the oxidized iron ( hematite) characteristic of drought conditions. Near the equator, Pangaea began to consolidate from the plates containing North America and Europe, further raising the northern Appalachian Mountainsand forming the Caledonian Mountainsin Great Britainand Scandinavia. The southern continents remained tied together in the supercontinent of Gondwana. The remainder of modern Eurasia lay in the Northern Hemisphere. Sea levels were high worldwide, and much of the land lay submerged under shallow seas. The deep, enormous Panthalassa (the "universal ocean") covered the rest of the planet. Other minor oceans were Paleo-Tethys, Proto-Tethys, Rheic Ocean, and Ural Ocean (which was closed during the collision with Siberia and Baltica).
The Carboniferous extends from about 359.2 ± 2.5 Ma (ICS 2004), to about 299.0 ± 0.8 Ma (ICS 2004).A global drop in sea level at the end of the Devonian reversed early in the
Carboniferous; this created the widespread epicontinental seas and carbonate deposition of the Mississippian. [Steven M. Stanley, "Earth System History." (New York: W.H. Freeman and Company, 1999), 414.] There was also a drop in south polar temperatures; southern Gondwanaland was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not. [Stanley, 414.] These conditions apparently had little effect in the deep tropics, where lush coalswamps flourished within 30 degrees of the northernmost glaciers. [Stanley, 416.] A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. [Stanley, 414.] This sea-level drop and the associated unconformity in North America separate the Mississippian periodfrom the Pennsylvanian period. [Stanley, 414.] The Carboniferous was a time of active mountain-building, as the supercontinent Pangea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America-Europe ( Laurussia) along the present line of eastern North America. This continental collision resulted in the Hercynian orogenyin Europe, and the Alleghenian orogenyin North America; it also extended the newly-uplifted Appalachians southwestward as the Ouachita Mountains. [Stanley, 414-6.] In the same time frame, much of present eastern Eurasianplate welded itself to Europe along the line of the Ural mountains. During the Late Carboniferous Pangaea was shaped like an "O". There were two major oceans in the Carboniferous - Panthalassa and Paleo-Tethys, which was inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and eventually closed - the Rheic Ocean(closed by the assembly of South and North America), the small, shallow Ural Ocean(which was closed by the collision of Balticaand Siberia continents, creating the Ural Mountains) and Proto-Tethys Ocean.
The Permian extends from about 299.0 ± 0.8 Ma (ICS 2004) to 251.0 ± 0.4 Ma (ICS 2004).During the
Permian, all the Earth's major land masses except portions of East Asia were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean (" Panthalassa", the "universal sea"), and the Paleo- TethysOcean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmasses create climates with extreme variations of heat and cold ("continental climate") and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea.
MA (million years ago)
The Mesozoic extended roughly from 251 Ma (ICS 2004) to 65 Ma (ICS 2004). After the vigorous convergent plate mountain-building of the late
MA (million years ago)
Paleozoic, Mesozoictectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the supercontinent Pangaea. Pangaea gradually split into a northern continent, Laurasia, and a southern continent, Gondwana. This created the passive continental marginthat characterizes most of the Atlanticcoastline (such as along the U.S. East Coast) today.
The Triassic period extends from about 251 ± 0.4 to 199.6 ± 0.6 Ma (ICS 2004). During the
Triassic, almost all the Earth's land mass was concentrated into a single supercontinentcentered more or less on the equator, called Pangaea("all the land"). This took the form of a giant " Pac-Man" with an east-facing "mouth" constituting the Tethys sea, a vast gulf that opened farther westward in the mid-Triassic, at the expense of the shrinking Paleo-Tethys Ocean, an ocean that existed during the Paleozoic. The remainder was the world-ocean known as Panthalassa("all the sea"). All the deep-ocean sediments laid down during the Triassic have disappeared through subductionof oceanic plates; thus, very little is known of the Triassic open ocean. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated. The first nonmarine sediments in the riftthat marks the initial break-up of Pangea—which separated New Jerseyfrom Morocco—are of Late Triassic age; in the U.S., these thick sediments comprise the Newark Group.cite web
url = http://rainbow.ldeo.columbia.edu/courses/v1001/10.html
title = Triassic world
accessdate = 2007-07-19
publisher = ] Because of the limited shoreline of one super-continental mass, Triassic marine deposits are globally relatively rare, despite their prominence in
Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west. Thus Triassic stratigraphyis mostly based on organisms living in lagoons and hypersaline environments, such as "Estheria" crustaceans. [Sereno, P. C., 1993, The pectoral girdle and forelimb of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology, v. 13, no. 4, p. 425-450.]
The Jurassic period extends from about 199.6 ± 0.6 Ma (ICS 2004) to 145.4 ± 4.0 Ma (ICS 2004).During the early
Jurassic, the supercontinent Pangaeabroke up into the northern supercontinent Laurasiaand the southern supercontinent Gondwana; the Gulf of Mexicoopened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic Oceanwas relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart.cite web
url = http://www.scotese.com/late1.htm
title = Pangea Begins to Rift Apart
accessdate = 2007-07-19
publisher = C. R. Scotese] The Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed. The Jurassic geological record is good in western
Europe, where extensive marine sequences indicate a time when much of the continent was submerged under shallow tropical seas; famous locales include the Jurassic Coast World Heritage Siteand the renowned late Jurassic " lagerstätten" of Holzmadenand Solnhofen.cite web
url = http://www.urweltmuseum.de/Englisch/museum_eng/Geologie_eng/Tektonik_eng.htm
title = Land and sea during Jurassic
accessdate = 2007-07-19
publisher = Urwelt museum hauff] In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. [cite web |url=http://www.nationalatlas.gov/articles/geology/legend/ages/jurassic.html |title=Jurassic Rocks - 208 to 146 million years ago |accessdate=2007-07-19 |work=nationalatlas.gov |publisher= United States Department of the Interior ] Though the epicontinental
Sundance Sealeft marine deposits in parts of the northern plains of the United Statesand Canadaduring the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation. The first of several massive batholiths were emplaced in the northern Cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. [Monroe and Wicander, 607.] Important Jurassic exposures are also found in Russia, India, South America, Japan, Australasia, and the United Kingdom.
Cretaceousperiod] The Cretaceous period extends from about 145.5 ± 4.0 Ma (ICS 2004) to about 65.5 ± 0.3 Ma (ICS 2004).During the Cretaceous, the late Paleozoic- early Mesozoic supercontinentof Pangaeacompleted its breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Oceanwidened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogenywas followed by the Sevier and Laramide orogenies. Though Gondwana was still intact in the beginning of the Cretaceous, Gondwanaitself broke up as South America, Antarcticaand Australiarifted away from Africa(though Indiaand Madagascarremained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Seacontinued to narrow. Broad shallow seas advanced across central North America(the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coalbeds. At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged. [Dougal Dixon et al., "Atlas of Life on Earth", (New York: Barnes & Noble Books, 2001), p. 215.] The Cretaceous is justly famous for its chalk; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic. [Stanley, Steven M. "Earth System History." New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 p. 280] Mid-ocean ridgeactivity--or rather, the circulation of seawater through the enlarged ridges--enriched the oceans in calcium; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nannoplankton. [Stanley, pp. 279-81] These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous Hell Creek Formation. Other important Cretaceous exposures occur in Europeand China. In the area that is now India, massive lavabeds called the Deccan Trapswere laid down in the very late Cretaceous and early Paleocene.
The Cenozoic era covers the 65.5 million years since the
Cretaceous-Tertiary extinction event. The Cenozoicera is ongoing. By the end of the Mesozoicera, the continents had rifted into nearly their present form. Laurasiabecame North Americaand Eurasia, while Gondwanasplit into South America, Africa, Australia, Antarcticaand the Indian subcontinent, which collided with the Asian plate. This impact also gave rise to the Himalayas. The Tethys Sea, which had separated the northern continents from Africa and India, began to close up, forming the Mediterranean sea.
The Paleogene (alternatively Palaeogene) period is a unit of
geologic timethat began 65.5 ± 0.3 and ended 23.03 ± 0.05 Ma (ICS 2004) and comprises the first part of the Cenozoicera.This period consists of the Paleocene, Eocene, and OligoceneEpochs.
The Paleocene, lasted from 65.5 ± 0.3 Ma (ICS 2004) to 55.8 ± 0.2 Ma (ICS 2004).In many ways, the
Paleocenecontinued processes that had begun during the late Cretaceous Period. During the Paleocene, the continents continued to drift toward their present positions. Supercontinent Laurasiahad not yet separated into three continents - Europeand Greenlandwere still connected North Americaand Asiawere still intermittently joined by a land bridge, while Greenland and North America were beginning to separate. Hooker, J.J., "Tertiary to Present: Paleocene", pp. 459-465, Vol. 5. of Selley, Richard C., L. Robin McCocks, and Ian R. Plimer, Encyclopedia of Geology, Oxford: Elsevier Limited, 2005. ISBN 0-12-636380-3] The Laramide orogenyof the late Cretaceous continued to uplift the Rocky Mountainsin the American west, which ended in the succeeding epoch. South and North America remained separated by equatorial seas (they joined during the Neogene); the components of the former southern supercontinent Gondwanalandcontinued to split apart, with Africa, South America, Antarcticaand Australiapulling away from each other. Africa was heading north towards Europe, slowly closing the Tethys Ocean, and Indiabegan its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas.
Eocene(55.8 ± 0.2 - 33.9 ± 0.1 Ma (ICS 2004)), the continents continued to drift toward their present positions. At the beginning of the period, Australiaand Antarctica remained connected, and warm equatorial currents mixed with colder Antarctic waters, distributing the heat around the world and keeping global temperatures high. But when Australia split from the southern continent around 45 mya, the warm equatorial currents were deflected away from Antarctica, and an isolated cold water channel developed between the two continents. The Antarctic region cooled down, and the ocean surrounding Antarctica began to freeze, sending cold water and icefloes north, reinforcing the cooling. The northern supercontinentof Laurasiabegan to break up, as Europe, Greenlandand North Americadrifted apart. In western North America, mountain building started in the Eocene, and huge lakes formed in the high flat basins among uplifts. In Europe, the Tethys Seafinally vanished, while the uplift of the Alpsisolated its final remnant, the Mediterranean, and created another shallow sea with island archipelagos to the north. Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar. Indiacontinued its journey away from Africaand began its collision with Asia, folding the Himalayas into existence.
The Oligocene epoch extends from about 34 Ma (ICS 2004) to 23 Ma (ICS 2004).During the
Oligocenethe continents continued to drift toward their present positions. Antarcticacontinued to become more isolated and finally developed a permanent ice cap. Mountain building in western North Americacontinued, and the Alpsstarted to rise in Europeas the African plate continued to push north into the Eurasian plate, isolating the remnants of Tethys Sea. A brief marine incursion marks the early Oligocene in Europe. There appears to have been a land bridge in the early Oligocene between North Americaand Europesince the faunas of the two regions are very similar. During sometime in the Oligocene, South Americawas finally detached from Antarcticaand drifted north towards North America. It also allowed the Antarctic Circumpolar Currentto flow, rapidly cooling the continent.
Neogene Period is a unit of geologic time starting 23.03 ± 0.05 Ma (ICS 2004). The Neogene Period follows the
PaleogenePeriod. Under the current proposal of the International Commission on Stratigraphy(ICS), the Neogene would consist of the Miocene, Pliocene, Pleistocene, and Holoceneepochs and continue until the present. [Lourens, L., Hilgen, F., Shackleton, N.J., Laskar, J., Wilson, D., (2004) “The Neogene Period”. In: Gradstein, F., Ogg, J., Smith, A.G. (Eds.), "Geologic Time Scale" Cambridge University Press, Cambridge.]
The Miocene extends from about 23.03 to 5.332 Ma (ICS 2004).During the
Miocenecontinents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South Americaand North Americawas absent, although South America was approaching the western subduction zone in the Pacific Ocean, causing both the rise of the Andesand a southward extension of the Meso-Americanpeninsula. Indiacontinued to collide with Asia, creating more mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africacollided with Eurasiain the Turkish- Arabian region between 19 and 12 Ma (ICS 2004) . Subsequent uplift of mountains in the western Mediterraneanregion and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the Messinian salinity crisis) near the end of the Miocene.
The Pliocene extends from 5.332 Ma (ICS 2004) to 1.806 Ma (ICS 2004).During the
Pliocenecontinents continued to drift toward their present positions, moving from positions possibly as far as convert|250|km|mi|0 from their present locations to positions only 70 km from their current locations. South Americabecame linked to North America through the Isthmus of Panamaduring the Pliocene, bringing a nearly complete end to South America's distinctive marsupial faunas. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean. Africa's collision with Europeformed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. Sea level changes exposed the land-bridge between Alaskaand Asia. Near the end of the Pliocene, about 2.58 Ma (the start the of the QuaternaryPeriod), the current ice age began.
The Pleistocene extends from 1,808,000 to 11,550 years before present (ICS 2004). The modern
continents were essentially at their present positions during the Pleistocene, the plates upon which they sit probably having moved no more than convert|100|km|mi|0 relative to each other since the beginning of the period.
The sum of transient factors acting at the Earth's surface is cyclical: climate, ocean currents and other movements, wind currents,
temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glacial advances of the Pleistocene were caused by the same factors.
The Holocene epoch began approximately 11,550 calendar years before present (ICS 2004) and continues to the present.During the
Holocene, continental motions have been less than a kilometer. However, ice melt caused world sea levels to rise about convert|35|m|ft|0 in the early part of the Holocene. In addition, many areas above about 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as convert|180|m|ft|0 over the late Pleistocene and Holocene, and are still rising today. The sea level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea. Holocene marine fossils are known from Vermont, Quebec, Ontario, and Michigan. Other than higher latitude temporary marine incursions associated with glacial depression, Holocene fossils are found primarily in lakebed, floodplain, and cave deposits. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any likely upthrusting of non-glacial origin. Post-glacial reboundin the Scandinaviaregion resulted in the formation of the Baltic Sea. The region continues to rise, still causing weak earthquakes across Northern Europe. The equivalent event in North America was the rebound of Hudson Bay, as it shrank from its larger, immediate post-glacial Tyrrell Seaphase, to near its present boundaries.
* [http://www.tufts.edu/as/wright_center/cosmic_evolution/docs/splash.html Cosmic Evolution] — a detailed look at events from the origin of the universe to the present
*Valley, John W. “ [http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0005FA5D-5F7C-1333-9F7C83414B7F0000 A Cool Early Earth?] ” "
Scientific American". 2005 Oct:58–65. – discusses the timing of the formation of the oceans and other major events in Earth’s early history.
*Davies, Paul. “ [http://www.guardian.co.uk/science/story/0,3605,1671164,00.html Quantum leap of life] ”. "
The Guardian". 2005 Dec 20. – discusses speculation into the role of quantum systems in the origin of life
* [http://www.johnkyrk.com/evolution.html Evolution timeline] (uses Shockwave). Animated story of life since about 13,700,000,000 shows everything from the big bang to the formation of the earth and the development of bacteria and other organisms to the ascent of man.
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=0005FA5D-5F7C-1333-9F7C83414B7F0000 Scientific American Magazine (October 2005 Issue) A Cool Early Earth?]
* [http://cosmographica.com/gallery/portfolio/portfolio2007/content/442_CoolEarlyEarth_large.html Artist's Conception of Cold Early Earth]
* [http://www.mala.bc.ca/~johnstoi/essays/Hutton.htm Theory of the Earth]
* [http://www.uwmc.uwc.edu/geography/hutton/hutton.htm Theory of the Earth & Abstract of the Theory of the Earth]
Wikimedia Foundation. 2010.
Look at other dictionaries:
History of Earth — The history of Earth covers approximately 4.6 billion years (4,567,000,000 years), from Earth’s formation out of the solar nebula to the present. This article presents a broad overview, summarizing the leading, most current scientific… … Wikipedia
Geological history — describes geological events that account for the stratigraphy, petrology and structure (see structural geology) seen in rocks or earth materials.See geologic timescale … Wikipedia
Geological history of India — The geological history of India started with the geological evolution of rest of the Earth i.e. 4.57 bya (billion years ago). India has a diverse geology. Different regions in India contain rocks of all types belonging to different geologic… … Wikipedia
History of the Earth — For the history of modern humans, see History of the world. Geological time put in a diagram called a geological clock, showing the relative lengths of the eons of the Earth s history The history of the Earth describes the most important events… … Wikipedia
Earth — This article is about the planet. For other uses, see Earth (disambiguation). Earth … Wikipedia
History — This article is about the academic discipline. For a general history of human beings, see History of the world. For other uses, see History (disambiguation). Historia (Allegory of History) By Nikolaos Gysis (1892) … Wikipedia
Geological features of the solar system — Recommendation Geology of solar terrestrial planets This is a directory of lists of geological features on other planets, moons and asteroids (in order of increasing distance of the Sun): = Mercury = * List of craters on Mercury * List of… … Wikipedia
History of the world (disambiguation) — The history of the world may refer to:*History of Earth, the natural history of the planet Earth:*For a geological history of Earth, please see Geologic time scale:*For a biological history, please see Timeline of evolution *History of the world … Wikipedia
Geological Museum of China — Beijing Geological Museum The Geol … Wikipedia
History of the Pacific Islands — covers the history of the islands in the Pacific Ocean.HistoriesAustraliaThe written history of Australia began when Dutch explorers first sighted the country in the 17th century. The interpretation of the history of Australia is currently a… … Wikipedia