Geological history of Earth
The Cenozoic era covers the 65.5 million years since the Cretaceous-Tertiary extinction event. The Cenozoic era is ongoing. By the end of the Mesozoic era, the continents had rifted into nearly their present form. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and 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.
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Paleogene Period
The Paleogene (alternatively Palaeogene) period is a unit of geologic time that began 65.5 ± 0.3 and ended 23.03 ± 0.05 Ma (ICS 2004) and comprises the first part of the Cenozoic era. This period consists of the Paleocene, Eocene, and Oligocene Epochs.
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Paleocene Epoch
The Paleocene, lasted from 65.5 ± 0.3 Ma (ICS 2004) to 55.8 ± 0.2 Ma (ICS 2004). In many ways, the Paleocene continued processes that had begun during the late Cretaceous Period. During the Paleocene, the continents continued to drift toward their present positions. Supercontinent Laurasia had not yet separated into three continents - Europe and Greenland were still connected North America and Asia were still intermittently joined by a land bridge, while Greenland and North America were beginning to separate.[29] The Laramide orogeny of the late Cretaceous continued to uplift the Rocky Mountains in 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 Gondwanaland continued to split apart, with Africa, South America, Antarctica and Australia pulling away from each other. Africa was heading north towards Europe, slowly closing the Tethys Ocean, and India began its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas.
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Eocene Epoch
During the 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, Australia and 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 supercontinent of Laurasia began to break up, as Europe, Greenland and North America drifted 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 Sea finally vanished, while the uplift of the Alps isolated 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. India continued its journey away from Africa and began its collision with Asia, folding the Himalayas into existence.
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Oligocene Epoch
The Oligocene epoch extends from about 34 Ma (ICS 2004) to 23 Ma (ICS 2004). During the Oligocene the continents continued to drift toward their present positions. Antarctica continued to become more isolated and finally developed a permanent ice cap. Mountain building in western North America continued, and the Alps started to rise in Europe as 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 America and Europe since the faunas of the two regions are very similar. During sometime in the Oligocene, South America was finally detached from Antarctica and drifted north towards North America. It also allowed the Antarctic Circumpolar Current to flow, rapidly cooling the continent.
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Neogene Period
Neogene Period is a unit of geologic time starting 23.03 ± 0.05 Ma (ICS 2004). The Neogene Period follows the Paleogene Period. Under the current proposal of the International Commission on Stratigraphy (ICS), the Neogene would consist of the Miocene, Pliocene, Pleistocene, and Holocene epochs and continue until the present.[30]
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Miocene Epoch
The Miocene extends from about 23.03 to 5.332 Ma (ICS 2004). During the Miocene continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent, although South America was approaching the western subduction zone in the Pacific Ocean, causing both the rise of the Andes and a southward extension of the Meso-American peninsula. India continued to collide with Asia, creating more mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish-Arabian region between 19 and 12 Ma (ICS 2004) . Subsequent uplift of mountains in the western Mediterranean region 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.
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Pliocene Epoch
The Pliocene extends from 5.332 Ma (ICS 2004) to 1.806 Ma (ICS 2004). During the Pliocene continents continued to drift toward their present positions, moving from positions possibly as far as 250 kilometres (155 mi) from their present locations to positions only 70 km from their current locations. South America became linked to North America through the Isthmus of Panama during 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 Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. Sea level changes exposed the land-bridge between Alaska and Asia. Near the end of the Pliocene, about 2.58 Ma (the start the of the Quaternary Period), the current ice age began.
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Pleistocene Epoch
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 100 kilometres (62 mi) 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.
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Holocene Epoch
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 35 metres (115 ft) 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 180 metres (591 ft) 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 rebound in the Scandinavia region 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 Sea phase, to near its present boundaries.
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References
- ^ Dalrymple, G.B. (1991). The Age of the Earth. California: Stanford University Press. ISBN 0-8047-1569-6.
- ^ Canup, R. M.; Asphaug, E. (Fall Meeting 2001). "An impact origin of the Earth-Moon system". Abstract #U51A-02, American Geophysical Union. Retrieved on 2007-03-10.
- ^ R. Canup and E. Asphaug (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation". Nature 412: 708–712. doi:.
- ^ Morbidelli, A.; Chambers, J.; Lunine, J. I.; Petit, J. M.; Robert, F.; Valsecchi, G. B.; Cyr, K. E. (2000). "Source regions and time scales for the delivery of water to Earth". Meteoritics & Planetary Science 35 (6): 1309–1320.
- ^ Murphy, J. B.; Nance, R. D. (1965). "How do supercontinents assemble?". American Scientist 92: 324–33. doi:.
- ^ Staff. Paleoclimatology - The Study of Ancient Climates. Page Paleontology Science Center. Retrieved on 2007-03-02.
- ^ 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
- ^ John D. Cooper, Richard H. Miller, and Jacqueline Patterson, A Trip Through Time: Principles of Historical Geology, (Columbus: Merrill Publishing Company, 1986), p. 180.
- ^ Stanley, pp. 302-3
- ^ Stanley, Steven M. (1999). Earth System History. New York: W.H. Freeman and Company, 315. ISBN 0-7167-2882-6.
- ^ Stanley, 315-18, 329-32
- ^ Stanley, 320-1, 325
- ^ Steven M. Stanley, Earth System History, (New York: W.H. Freeman and Company, 1999), 358.
- ^ Steven M. Stanley, Earth System History. (New York: W.H. Freeman and Company, 1999), 414.
- ^ Stanley, 414.
- ^ Stanley, 416.
- ^ Stanley, 414.
- ^ Stanley, 414.
- ^ Stanley, 414-6.
- ^ Triassic world. Retrieved on 2007-07-19.
- ^ 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.
- ^ Pangea Begins to Rift Apart. C. R. Scotese. Retrieved on 2007-07-19.
- ^ Land and sea during Jurassic. Urwelt museum hauff. Retrieved on 2007-07-19.
- ^ Jurassic Rocks - 208 to 146 million years ago. nationalatlas.gov. United States Department of the Interior. Retrieved on 2007-07-19.
- ^ Monroe and Wicander, 607.
- ^ Dougal Dixon et al., Atlas of Life on Earth, (New York: Barnes & Noble Books, 2001), p. 215.
- ^ Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 p. 280
- ^ Stanley, pp. 279-81
- ^ 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
- ^ 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.
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External links
- Cosmic Evolution — a detailed look at events from the origin of the universe to the present
- Valley, John W. “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. “Quantum leap of life”. The Guardian. 2005 Dec 20. – discusses speculation into the role of quantum systems in the origin of life
- 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.
- Scientific American Magazine (October 2005 Issue) A Cool Early Earth?
- Artist's Conception of Cold Early Earth
- Theory of the Earth
- Theory of the Earth & Abstract of the Theory of the Earth
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