Pangaea, Pangæa or Pangea (IPAEng|pænˈdʒiːə [OED] , from παν, "pan", meaning "entire", and Γαῖα, "Gaea", meaning "Earth" in
Ancient Greek) was the supercontinentthat existed during the Paleozoicand Mesozoiceras about 250 million years ago, before the component continents were separated into their current configuration [Plate Tectonics and Crustal Evolution, Third Ed., 1989, by Kent C. Condie, Pergamon Press] .
The name was first used by the German originator of the
continental drifttheory, Alfred Wegener, in the 1920 edition of his book "The Origin of Continents and Oceans (Die Entstehung der Kontinente und Ozeane)", in which a postulated supercontinent Pangaea played a key role.
Configuration of Pangaea
Paleogeographic reconstructions show Pangaea as a roughly C-shaped landmass that was spread across the
equator. The body of waterthat was enclosed within the resulting crescent has been named the Tethys Sea. Owing to Pangaea's massive size, the inland regions appear to have been very dry. The large supercontinent would potentially have allowed terrestrial animals to migrate freely.
The vast ocean that surrounded the
supercontinentof Pangaea has been named Panthalassa, which means "all seas". The break-up of Pangaea began about 180 million years ago (180 mya) in the JurassicPeriod, first into two supercontinents ( Gondwanato the south and Laurasiato the north), thereafter into the continents we have today.
Formation of Pangaea
Rodinia, which formed 1.3 billion years ago during the Proterozoic, was the supercontinent from which all subsequent continents, sub or super, derived. Rodinia does not preclude the possibility of prior supercontinents as the breakup and formation of supercontinents appears to be cyclical through Earth's 4.6 billion years. Gondwanafollowed with several iterations before the formation of Pangaea, which succeeded Pannotia, before the beginning of the Paleozoic Era(545 Ma) and the Phanerozoic Eon.
The minor supercontinent of
Proto-Laurasiadrifted away from Gondwana and moved across the Panthalassic Ocean. A new ocean was forming between the two continents, the Proto-Tethys Ocean. Soon, Proto-Laurasia drifted apart itself to create Laurentia, Siberia and Baltica. The rifting also spawned two new oceans, the Iapetus and Khanty Oceans. Baltica remained east of Laurentia, and Siberia sat northeast of Laurentia.
Cambrianthe independent continent of Laurentiaon what would become North Americasat on the equator, with three bordering oceans: the Panthalassic Oceanto the north and west, the Iapetus Oceanto the south and the Khanty Oceanto the east. In the Earliest Ordovician, the microcontinent of Avalonia, a landmass that would become the northeastern United States, Nova Scotiaand England, broke free from Gondwana and began its journey to Laurentia. [cite book| last =Stanley| first = Steven| authorlink = Steven M. Stanley| title = Earth System History| date = 1998| location = USA| pages = 355-359 ] Balticacollided with Laurentia by the end of the Ordovician and northern Avalonia collided with Baltica and Laurentia. Laurentia, Baltica and Avalonia formed to create a minor supercontinent of Euramericaor Laurussia, closing the Iapetus Ocean, while the Rheic Oceanexpanded in the southern coast of Avalonia. The collision also resulted in the formation of the northern Appalachians. Siberia sat near Euramerica, with the Khanty Oceanbetween the two continents. While all this was happening, Gondwana drifted slowly towards the South Pole. This was the first step of the formation of Pangaea. [cite book| last =Stanley| first = Steven| authorlink = Steven M. Stanley| title = Earth System History| date = 1998| location = USA| pages = 386-392 ]
The second step in the formation of Pangaea was the collision of Gondwana with
Euramerica. By Siluriantime, Baltica had already collided with Laurentia to form Euramerica. Avaloniahadn't collided with Laurentiayet, and a seaway between them, a remnant of the Iapetus Ocean, was still shrinking as Avalonia slowly inched towards Laurentia.
southern Europefragmented from Gondwana and started to head towards Euramerica across the newly formed Rheic Oceanand collided with southern Balticain the Devonian, though this microcontinent was an underwater plate. The Iapetus Ocean's sister ocean, the Khanty Ocean, was also shrinking as an island arc from Siberia collided with eastern Baltica (now part of Euramerica). Behind this island arcwas a new ocean, the Ural Ocean.
By late Silurian time, North and South China rifted away from Gondwana and started to head northward across the shrinking Proto-Tethys Ocean, and on its southern end the new
Paleo-Tethys Oceanwas opening. In the Devonian Period, Gondwana itself headed towards Euramerica, which caused the Rheic Ocean to shrink.
In the Early
Carboniferous, northwest Africahad touched the southeastern coast of Euramerica, creating the southern portion of the Appalachian Mountains, and the Meseta Mountains. South Americamoved northward to southern Euramerica, while the eastern portion of Gondwana ( India, Antarcticaand Australia) headed towards the South Pole from the equator.
North China and South China were on independent continents. The
Kazakhstaniamicrocontinent had collided with Siberia (Siberia had been a separate continent for millions of years since the deformation of the supercontinent Pannotia) in the Middle Carboniferous.
Kazakhstaniacollided with Balticain the Late Carboniferous, closing the Ural Oceanbetween them, and the western Proto-Tethys in them ( Uralian orogeny), causing the formation of the Ural Mountains, and the formation of the supercontinent of Laurasia. This was the last step of the formation of Pangaea.
Meanwhile, South America had collided with southern
Laurentia, closing the Rheic Ocean, and forming the southernmost part of the Appalachiansand Ouachita Mountains. By this time, Gondwana was positioned near the South Pole, and glaciers were forming in Antarctica, India, Australia, southern Africa and South America. The North Chinablock collided with Siberiaby Late Carboniferous time, completely closing the Proto-Tethys Ocean.
Permiantime, the Cimmerian platerifted away from Gondwana and headed towards Laurasia, with a new ocean forming in its southern end, the Tethys Ocean, and the closure of the Paleo-Tethys Ocean. Most of the landmasses were all in one. By the TriassicPeriod, Pangaea rotated a little, in a southwest direction. The Cimmerian plate was still travelling across the shrinking Paleo-Tethys, until the Middle Jurassictime. The Paleo-Tethys had closed from west to east, creating the Cimmerian Orogeny. Pangaea looked like a "C", with an ocean inside the "C", the new Tethys Ocean. Pangaea had rifted by the Middle Jurassic, and its deformation is explained below.
Evidence of Pangaea's existence
Fossilevidence 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 Gandu, South Africa, Indiaand Australia, 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 only been found in localized regions of the coasts of Braziland West Africa. [Benton, M.J. "Vertebrate Palaeontology". Third edition (Oxford 2005), 25.]
Additional evidence for Pangaea is found in the
geologyof adjacent continents, including matching geological trends between the eastern coast of South Americaand the western coast of Africa.
polar ice capof the CarboniferousPeriod covered the southern end of Pangaea. Glacial deposits, specifically till, of the same age and structure are found on many separate continents which would have been together in the continent of Pangaea. [Barbara W. Murck, Brian J. Skinner, "Geology Today: Understanding Our Planet, Study Guide", Wiley, ISBN 978-0-471-32323-5]
Rifting and break-up of Pangaea
There were three major phases in the break-up of Pangaea. The first phase began in the Early-
Middle Jurassic, when Pangaea created a rift from the Tethys Ocean in the east and the Pacificin the west. The rifting took place between North America and Africa, and produced multiple failed rifts. The rift resulted in a new ocean, the Atlantic Ocean.
The Atlantic Ocean did not open uniformly; rifting began in the north-central Atlantic. The
South Atlanticdid not open until the Cretaceous. Laurasia started to rotate clockwise and moved northward with North America to the north, and Eurasiato the south. The clockwise motion of Laurasia also led to the closing of the Tethys Ocean. Meanwhile, on the other side of Africa, new rifts were also forming along the adjacent margins of east Africa, Antarctica and Madagascarthat would lead to the formation of the southwestern Indian Oceanthat would also open up in the Cretaceous.
The second major phase in the break-up of Pangaea began in the
Early Cretaceous(150–140 Ma), when the minor supercontinent of Gondwana separated into four multiple continents (Africa, South America, India and Antarctica/Australia). About 200 Ma, the continent of Cimmeria, as mentioned above (see "Formation of Pangaea"), collided with Eurasia. However, a subduction zone was forming, as soon as Cimmeria collided.
This subduction zone was called the
Tethyan Trench. This trench might have subducted what is called the Tethyan mid-ocean ridge, a ridge responsible for the Tethys Ocean's expansion. It probably caused Africa, India and Australia to move northward. In the Early Cretaceous, Atlantica, today's South America and Africa, finally separated from eastern Gondwana (Antarctica, India and Australia), causing the opening of a "South Indian Ocean". 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,
Madagascarand India began to separate from Antarctica and moved northward, opening up the Indian Ocean. Madagascar and India separated from each other 100–90 Ma in the Late Cretaceous. India continued to move northward toward Eurasia at 15 centimeters (6 in) per year (a plate tectonic record), closing the Tethys Ocean, while Madagascar stopped and became locked to the African Plate. New Zealand, New Caledoniaand the rest of Zealandia began to separate from Australia, moving eastward towards the Pacificand opening the Coral Seaand Tasman Sea.
The third major and final phase of the break-up of Pangaea occurred in the early
Cenozoic( Paleoceneto Oligocene). North America/ Greenlandbroke free from Eurasia, opening the Norwegian Seaabout 60–55 Ma. The Atlantic and Indian Oceans continued to expand, closing the Tethys Ocean.
Meanwhile, Australia split from Antarctica and moved rapidly northward, just as India did more than 40 million years earlier, and is currently on a collision course with
eastern Asia. Both Australia and India are currently moving in a northeastern direction at 5–6 centimeters (2–3 in) per year. Antarctica has been near or at the South Pole since the formation of Pangaea about 280 Ma. India started to collide with Asiabeginning about 35 Ma, forming the Himalayan orogeny, and also finally closing the Tethys Seaway; this collision continues today. The African Plate started to change directions, from west to northwest toward Europe, and South America began to move in a northward direction, separating it from Antarctica and allowing complete oceanic circulation around Antarctica for the first time, causing a rapid cooling of the continent and allowing glaciers to form. Other major events took place during the Cenozoic, including the opening of the Gulf of California, the uplift of the Alps, and the opening of the Sea of Japan. The break-up of Pangaea continues today in the Great Rift Valley; ongoing collisions may indicate the incipient creation of a new supercontinent.
In around 250 million years, all of the world's continents may be merged together in one landmass again as Amasia or
List of supercontinents
History of Earth
* [http://pubs.usgs.gov/publications/text/historical.html USGS Overview]
* In honor of
Alfred Wegener, at the Alfred Wegener Institute for Polar and Marine Research(AWI) an information system for georeferenced data from earth system research is named [http://www.pangaea.de/ "PANGAEA"]
* [http://www.tectonic-forces.org An explanation of tectonic forces]
* [http://www.foxnews.com/story/0,2933,248979,00.html Europe's First Stegosaurus Boosts Pangaea Theory]
* [http://www.scotese.com/newpage8.htm Map of Triassic Pangaea at Paleomaps]
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Look at other dictionaries:
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