Pangaea
Pangaea or Pangea (
Origin of the concept
The name "Pangaea" is derived from
The name "Pangaea" occurs in the 1920 edition of Die Entstehung der Kontinente und Ozeane, but only once, when Wegener refers to the ancient supercontinent as "the Pangaea of the Carboniferous".[11] Wegener used the Germanized form "Pangäa," but the name entered German and English scientific literature (in 1922[12] and 1926, respectively) in the Latinized form "Pangaea" (of the Greek "Pangaia"), especially due to a symposium of the American Association of Petroleum Geologists in November 1926.[13]
Wegener originally proposed that the breakup of Pangaea was due to
Evidence of existence
The geography of the continents bordering the Atlantic Ocean was the first evidence suggesting the existence of Pangaea. The seemingly close fit of the coastlines of North and South America with Europe and Africa was remarked on almost as soon as these coasts were charted. The first to suggest that these continents were once joined and later separated may have been Abraham Ortelius in 1596.[17] Careful reconstructions showed that the mismatch at the 500 fathoms (3,000 feet; 910 meters) contour was less than 130 km (81 mi), and it was argued that this was much too good to be attributed to chance.[18]
Additional evidence for Pangaea is found in the
Fossil evidence for Pangaea includes the presence of similar and identical species on continents that are now great distances apart. For example, fossils of the therapsid Lystrosaurus have been found in South Africa, India and Antarctica, alongside members of the Glossopteris flora, whose distribution would have ranged from the polar circle to the equator if the continents had been in their present position; similarly, the freshwater reptile Mesosaurus has been found in only localized regions of the coasts of Brazil and West Africa.[21]
Geologists can also determine
Formation
Pangaea is only the most recent supercontinent reconstructed from the geologic record. The formation of supercontinents and their breakup appears to have been cyclical through Earth's history. There may have been several others before Pangaea.
Paleomagnetic measurements help geologists determine the latitude and orientation of ancient continental blocks, and newer techniques may help determine longitudes.[23] Paleontology helps determine ancient climates, confirming latitude estimates from paleomagnetic measurements, and the distribution of ancient forms of life provides clues on which continental blocks were close to each other at particular geological moments.[24] However, reconstructions of continents prior to Pangaea, including the ones in this section, remain partially speculative, and different reconstructions will differ in some details.[25]
Previous supercontinents
The fourth-last supercontinent, called
According to one reconstruction,
Formation of Euramerica (Laurussia)
In the
Collision of Gondwana with Euramerica
The second step in the formation of Pangaea was the collision of Gondwana with Euramerica. By the middle of the Silurian, 430 Ma, Baltica had already collided with Laurentia, forming Euramerica, an event called the Caledonian orogeny. Avalonia had not yet collided with Laurentia, but as Avalonia inched towards Laurentia, the seaway between them, a remnant of the Iapetus Ocean, was slowly shrinking. Meanwhile, southern Europe broke off from Gondwana and began to move towards Euramerica across the Rheic Ocean. It collided with southern Baltica in the Devonian.[34]
By the late Silurian, Annamia and
The Variscan orogeny raised the
Formation of Laurasia
Western
By the
Life
Pangaea existed as a supercontinent for 160 million years, from its assembly around 335 million years ago (
The evolution of life in this time reflected the conditions created by the assembly of Pangaea. The union of most of the continental crust into one landmass reduced the extent of sea coasts. Increased erosion from uplifted continental crust increased the importance of floodplain and delta environments relative to shallow marine environments. Continental assembly and uplift also meant increasingly arid land climates, favoring the evolution of
The lack of oceanic barriers is thought to have favored cosmopolitanism, in which successful species attain wide geographical distribution. Cosmopolitanism was also driven by
Mass extinctions
The tectonics and geography of Pangaea may have worsened the Permian–Triassic extinction event or other extinctions. For example, the reduced area of continental shelf environments may have left marine species vulnerable to extinction.[49] However, no evidence for a species-area effect has been found in more recent and better characterized portions of the geologic record.[50][51] Another possibility is that reduced sea-floor spreading associated with the formation of Pangaea, and the resulting cooling and subsidence of oceanic crust, may have reduced the number of islands that could have served as refugia for marine species. Species diversity may have already been reduced prior to mass extinction events due to mingling of species possible when formerly separate continents were merged. However, there is strong evidence that climate barriers continued to separate ecological communities in different parts of Pangaea. The eruptions of the Emeishan Traps may have eliminated South China, one of the few continental areas not merged with Pangaea, as a refugium.[52]
Rifting and break-up
There were three major phases in the break-up of Pangaea.
Opening of the Atlantic
The Atlantic Ocean did not open uniformly; rifting began in the north-central Atlantic. The first breakup of Pangaea is proposed for the late Ladinian (230 Ma) with initial spreading in the opening central Atlantic. Then the rifting proceeded along the eastern margin of North America, the northwest African margin and the High, Saharan and Tunisian Atlas.[53]
Another phase began in the Early-Middle Jurassic (about 175 Ma), when Pangaea began to rift from the Tethys Ocean in the east to the Pacific Ocean in the west. The rifting that took place between North America and Africa produced multiple failed rifts. One rift resulted in a new ocean, the North Atlantic Ocean.[20]
The
Break-up of Gondwana
The second major phase in the break-up of Pangaea began in the Early Cretaceous (150–140 Ma), when the landmass of Gondwana separated into multiple continents (Africa, South America, India, Antarctica, and Australia). The subduction at Tethyan Trench probably caused Africa, India and Australia to move northward, causing the opening of a "South Indian Ocean". In the Early Cretaceous, Atlantica, today's South America and Africa, finally separated from eastern Gondwana (Antarctica, India and Australia). Then in the Middle Cretaceous, Gondwana fragmented to open up the South Atlantic Ocean as South America started to move westward away from Africa. The South Atlantic did not develop uniformly; rather, it rifted from south to north.
Also, at the same time,
Opening of the Norwegian Sea and break-up of Australia and Antarctica
The third major and final phase of the break-up of Pangaea occurred in the early Cenozoic (Paleocene to Oligocene). Laurasia split when North America/Greenland (also called Laurentia) broke free from Eurasia, opening the Norwegian Sea about 60–55 Ma. The Atlantic and Indian Oceans continued to expand, closing the Tethys Ocean.
Meanwhile, Australia split from Antarctica and moved quickly northward, just as India had done more than 40 million years before. Australia is currently on a collision course with
Climate change after Pangaea
The breakup of Pangaea was accompanied by outgassing of large quantities of
The expansion of the temperate climate zones that accompanied the breakup of Pangaea may have contributed to the diversification of the
See also
- History of Earth
- Potential future supercontinents: Pangaea Ultima, Novopangaea & Amasia
- Supercontinent cycle
- Wilson Cycle
References
- ^ "Pangaea". Lexico UK English Dictionary. Oxford University Press. Archived from the original on October 25, 2020.
- ^ "Pangea". Encyclopædia Britannica Inc. 2015.
- ^ ISBN 978-0-19-516589-0
- ^ "Pangaea". Online Etymology Dictionary.
- ^ Vergilius Mario, Publius. Georgicon, IV.462
- ^ Lucan. Pharsalia, I.679
- ^ Lewis, C.T. & al. "Pangaeus" in A Latin Dictionary. (New York), 1879.
- ^ Usener, H. Scholia in Lucani Bellum Civile, Vol. I. (Leipzig), 1869.
- scholiast on Lucan glossed Pangaea id est totum terra—"Pangaea: that is, all land"—as having received its name on account of its smooth terrain and unexpected fertility.[8]
- ^ Alfred Wegener: Die Entstehung der Kontinente. Dr. A. Petermann's Mitteilungen aus Justus Perthes' Geographischer Anstalt, 58(1): Gotha 1912
- ^ See:
- Wegener, Alfred, Die Entstehung der Kontinente und Ozeane, 2nd ed. (Braunschweig, Germany: F. Vieweg, 1920), p. 120: "Schon die Pangäa der Karbonzeit hatte so einen Vorderrand ... " [Already the Pangaea of the Carboniferous era had such a leading edge ...] (In the 1922 edition, see p. 130.)
- Wegener, A.; Krause, R.; Thiede, J. (2005). "Kontinental-Verschiebungen: Originalnotizen und Literaturauszüge"(Continental drift: the original notes and quotations). Berichte zur Polar- und Meeresforschung (Reports on Polar and Marine Research) 516. Alfred-Wegener-Institut: Bremerhaven, p. 4, n. 2
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- ^ Willem A. J. M. van Waterschoot van der Gracht (and 13 other authors): Theory of Continental Drift: a Symposium of the Origin and Movements of Land-masses of both Inter-Continental and Intra-Continental, as proposed by Alfred Wegener. X + 240 S., Tulsa, Oklahoma, United States, The American Association of Petroleum Geologists & London, Thomas Murby & Co.
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- ^ Kearey, Klepeis & Vine 2009, p. 2.
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- ^ ISBN 047174705X
- ^ Benton, M.J. (2005) Vertebrate Palaeontology. Third edition, Oxford, p. 25.
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- ^ Torsvik & Cocks 2017, pp. 161, 171–172, 237.
- ^ Torsvik & Cocks 2017, pp. 180–181, 198.
- ^ a b "Life of the Carboniferous". UC Museum of Paleontology. UC Berkeley. Retrieved 19 February 2021.
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- ^ "Jurassic Period: Life". UC Museum of Paleontology. UC Berkeley. Retrieved 19 February 2021.
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- ^ Erwin 1990, p. 83.
- ^ Erwin 1990, pp. 83–84.
- ^ Antonio Schettino, Eugenio Turco: Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions. In: Geophysical Journal International, Band 178, Ausgabe 2, August 2009, S. 1078–1097.
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