http://en.wikipedia.org/wiki/List_of_supercontinents
CONTENTS
· Vaalbara (~3.6 Ga ago). Evidence is the Yilgarn Craton, Western Australia and the worldwide Archean greenstone belts that were subsequently spread out across Gondwana and Laurasia.
· Ur (~3 Ga ago). Classified as the earliest known landmass. Ur, however, was probably the largest, perhaps even the only continent three billion years ago. While probably not a supercontinent, one can argue that Ur was a supercontinent for its time, even if it was smaller than Australia is today. Still, an older rock formation now located in Greenland dates back from Hadean times.
· Kenorland (~2.7 Ga ago). Neoarchean sanukitoid cratons and new continental crust formed Kenorland. Protracted tectonic magna plume rifting occurred 2.48 to 2.45 Ga and this contributed to the Paleoproterozoic glacial events in 2.45 to 2.22 Ga. Final breakup occurred ~2.1 Ga.
· Nena (~1.8 Ga)
· Columbia, also called Nuna (~1.8–1.5 Ga ago)
· Rodinia (~1.1 Ga–~750 million years ago)
· Pannotia, also called Vendian (~600–~540 million years ago)
· Oldredia (~418–~380 million years ago)
· Euramerica (~300 million years ago)
· Pangaea (~300–~200 million years ago)
· Laurasia (~510–~200 million years ago)
· Gondwana (~510–~180 million years ago)
Cratons are the masses of rock composing the basic, initial structure of continents; they have remained stable for billions of years throughout the process of the ocean crust being continually created and destroyed. Continental plates, containing the ancient cratons, have periodically collided and assembled in geologic periods of orogenesis (mountain building) to form supercontinents. A supercontinent is a landmass composed of more than one craton.
Supercontinents act as thermal lids, blocking the escape of Earth's internal heat, so the asthenosphere overheats. Eventually the lithosphere begins to dome upward, it cracks, magma wells upward and fragments of the supercontinent slide off the overswell. The East African Rift valleys are a modern-day example of this breaking apart. This cycle – the Wilson Cycle – of supercontinent formation, breakup, and dispersal, followed by convergence and patching through plate tectonics, occurs every 450 million years or so.
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Vaalbara is theorized to be Earth's first supercontinent, beginning its formation about 3,600 million years ago, completing its formation by about 3,100 million years ago and breaking up by 2,500 million years ago. The name Vaalbara is derived from the eastern South African Kaapvaal craton and the Pilbara craton in northwest Western Australia. (The name Vaalbara is derived from the last four letters of each craton's name.) These cratons were combined during the time of the Vaalbara supercontinent.
Identical radiometric ages of 3,470 ± 2 million years ago have been obtained for the ejecta from the oldest impact events in each craton. Remarkably similar structural sequences between these two cratons have been noted for the period between 3,500 to 2,700 million years ago.
Paleomagnetic data from two ultramafic complexes in the cratons showed that at 3,870 million years the two cratons could have been part of the same supercontinent. The reconstructed apparent polar wander path for the two cratons shows marked similarities. Both the Pilbara and Kaapvaal cratons show extensional faults which were active about the same time during felsic volcanism and coeval with the impact layers.
Continental plates have periodically collided and assembled in geologic periods of orogenesis (mountain building) to form supercontinents. The cycle of supercontinent formation, breakup, dispersal and reformation by plate tectonics occurs every 450 million years or so.
It is uncertain when Vaalbara began to break up; geochronological and palaeomagnetic evidence show that the two cratons had a rotational 30° latitudinal separation in the time period of 2.78 to 2.77 billion years ago, which indicates they were no longer joined after ~2,800 million years ago.
Ur was a supercontinent that formed 3,000 million years ago (3 billion) in the early Archean eon; perhaps the oldest continent on Earth, half a billion years older than Arctica, but it may have been preceded by one other supercontinent, Vaalbara, which is suggested to have formed about 3,600 to 3,100 million years ago. Ur joined with the continents Nena and Atlantica about 1,000 million years ago (1 billion) to form the supercontinent Rodinia. Ur survived as a single unit until it was sundered when the supercontinent Pangaea broke apart into Laurasia and Gondwana. Rocks that made up Ur are now parts of Africa, Australia, and India.
In the early period of Ur's existence, it was probably the only continent on Earth. Thus Ur is considered to be a supercontinent, even though it was probably smaller than Australia is now. Current day New Zealand has a vague resemblance to Ur, but rotated 90 degrees out of phase, and is about 1000 km too far South. When Ur was the only continent on Earth, all other land was in the form of small granite islands and small land-masses like Kenorland that were not large enough to be continents.
Kenorland was one of the earliest supercontinents on Earth. It is believed to have formed during the Neoarchaean Era ~2.7 billion years ago (2.7 Ga) by the accretion of Neoarchaean cratons and the formation of new continental crust. Kenorland comprised what later became Laurentia (the core of today's North America and Greenland), Baltica (today's Scandinavia and Baltic), Western Australia and Kalaharia.
Swarms of volcanic dikes and their paleomagnetic orientation as well as the existence of similar stratigraphic sequences permit this reconstruction. The core of Kenorland, the Baltic/Fennoscandian Shield, traces its origins back to over 3.1 Ga. The Yilgarn Craton (present-day Western Australia) contains zircon crystals in its crust that date back to 4.4 Ga.
Nena was an ancient minor supercontinent that consisted of the cratons of Arctica, Baltica, and East Antarctica. Forming about 1.8 billion years ago, the continent was part of the global supercontinent, Columbia. Nena is an acronym that derives from Northern Europe and North America.
Columbia, also known as Nuna and Hudsonland, was one of Earth's ancient supercontinents. It was first proposed by J.J.W. Rogers and M. Santosh (2002) and is thought to have existed approximately 1.8 to 1.5 billion years (Ga) ago in the Paleoproterozoic Era. Zhao et al. (2002) proposed that the assembly of the supercontinent Columbia (Nuna) was completed by global-scale collisional events during 2.1–1.8 Ga. It consisted of the proto-cratons that made up the former continents of Laurentia, Baltica, Ukrainian Shield, Amazonian Shield, Australia, and possibly Siberia, North China, and Kalaharia as well. The evidence of Columbia's existence is based upon geological and paleomagnetic data.
Columbia is estimated to have been about 12,900 kilometres from North to South, and about 4,800 km across at its broadest part. The east coast of India was attached to western North America, with southern Australia against western Canada. Most of South America spun so that the western edge of modern-day Brazil lined up with eastern North America, forming a continental margin that extended into the southern edge of Scandinavia.
Columbia was assembled along global-scale 2.0–1.8 Ga collisional orogens and contained almost all of Earth’s continental blocks. The cratonic blocks in South America and West Africa were welded by the 2.1-2.0 Ga Transamazonian and Eburnean Orogens; the Kaapvaal and Zimbabwe cratons in southern Africa were collided along the ~2.0 Ga Limpopo Belt; the cratonic blocks of Laurentia were sutured along the 1.9–1.8 Ga Trans-Hudson, Penokean, Taltson–Thelon, Wopmay, Ungava, Torngat, and Nagssugtoqidain Orogens; the Kola, Karelia, Volgo-Uralia, and Sarmatia cratons in Baltica (Eastern Europe) were joined by the 1.9–1.8 Ga Kola–Karelia, Svecofennian, Volhyn-Central Russian, and Pachelma Orogens; the Anabar and Aldan Cratons in Siberia were connected by the 1.9–1.8 Ga Akitkan and Central Aldan Orogens; the East Antarctica and an unknown continental block were joined by the Transantarctic Mountains Orogen; the South and North Indian Blocks were amalgamated along the Central Indian Tectonic Zone; and the Eastern and Western Blocks of the North China Craton were welded together by the ~1.85 Ga Trans-North China Orogen.
Columbia began to fragment about 1.6 Ga ago, associated with continental rifting along the western margin of Laurentia (Belt-Purcell Supergroup), eastern India (Mahanadi and the Godavari), southern margin of Baltica (Telemark Supergroup), southeastern margin of Siberia (Riphean aulacogens), northwestern margin of South Africa (Kalahari Copper Belt), and northern margin of the North China Block (Zhaertai-Bayan Obo Belt).
The fragmentation corresponded with widespread anorogenic magmatic activity, forming anorthosite-mangerite-charnockite-granite (AMCG) suites in North America, Baltica, Amazonia, and North China, and continued until the final breakup of the supercontinent at about 1.3-1.2 Ga, marked by the emplacement of the 1.27 Ga Mackenzie and 1.24 Ga Sudbury mafic dike swarms in North America.
In geology, Rodinia (from the Russian rodítj, meaning "to give birth", or ródina, meaning "The Motherland") is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era. It formed at ~1.0 Ga by accretion and collision of fragments produced by breakup of the older supercontinent, Columbia, which was assembled by global-scale 2.0-1.8 Ga collisional events. Rodinia has entered popular consciousness as one of the two great supercontinents of earth history, the other being Pangaea.
Rodinia broke up in the Neoproterozoic and its continental fragments were re-assembled to form Pangaea 300-250 million years ago. In contrast with Pangaea, little is known yet about the exact configuration and geodynamic history of Rodinia. Paleomagnetic evidence provides some clues to the paleolatitude of individual pieces of the Earth's crust, but not to their longitude, which geologists have pieced together by comparing similar geologic features, often now widely dispersed.
The extreme cooling of the global climate around 700 million years ago (the so-called Snowball Earth of the Cryogenian period) and the rapid evolution of primitive life during the subsequent Ediacaran and Cambrian periods are often thought to have been triggered by the breaking up of Rodinia.
The idea that a supercontinent existed in the early Neoproterozoic arose in the 1970s, when geologists determined that orogens of this age exist on virtually all cratons. Examples are the Grenville orogeny in North America, the Uralian orogeny in Siberia and the Dalslandian orogeny in Europe.
Since then, many alternative reconstructions have been proposed for the configuration of the cratons in this supercontinent. Most of these reconstructions are based on the correlation of the orogens on different cratons. Though the configuration of the core cratons in Rodinia is now reasonably well known, recent reconstructions still differ in many details. Geologists try to decrease the uncertainties by collecting geological and paleomagnetical data.
Rodinia's landmass was probably centered south of the equator. Most reconstructions show Rodinia's core was formed by the North American craton (the later paleocontinent of Laurentia), surrounded in the southeast with the East European craton (the later paleocontinent of Baltica), the Amazonian craton ("Amazonia") and the West African craton; in the south with the Rio de la Plata and São Francisco cratons; in the southwest with the Congo and Kalahari cratons; and in the northeast with Australia, India and eastern Antarctica. The positions of Siberia and North and South China north of the North American craton differ strongly depending on the reconstruction.
Little is known about the paleogeography before the formation of Rodinia. Paleomagnetic and geologic data is only definite enough to form reconstructions that are generally agreed on from the breakup of Rodinia onwards. Rodinia was probably formed between 1100 and 1000 million years ago and broke up again before 750 million years ago. Rodinia was surrounded by the superocean geologists are calling Mirovia (from Russian мировой, mirovoy, meaning "global"; Родина, rodina, meaning "motherland").
In contrast to Rodinia's formation, the movements of continental masses during and since its breakup are fairly well understood. Rifting did not start everywhere simultaneously. Extensive lava flows and volcanic eruptions of Neoproterozoic age are found on most continents, evidence for large scale rifting about 750 million years ago. As early as 850 and 800 million years ago, a rift developed between the continental masses of present-day Australia, eastern Antarctica, India and the Congo and Kalahari cratons on one side and later Laurentia, Baltica, Amazonia and the West African and Rio de la Plata cratons on the other. This rift developed into the Adamastor Ocean during the Ediacaran.
The first group of cratons would eventually, around 550 million years ago (on the boundary between the Ediacaran and Cambrian), fuse again with Amazonia, West Africa and the Rio de la Plata craton. This tectonic phase is called the Pan-African orogeny. It created a configuration of continents that would remain stable for hundreds of millions of years in the form of the continent Gondwana.
In a separate rifting event about 610 million years ago (halfway in the Ediacaran period), the Iapetus Ocean formed. The eastern part of this ocean formed between Baltica and Laurentia, the western part between Amazonia and Laurentia. Because the exact moments of this separation and the partially contemporaneous Pan-African orogeny are hard to correlate, it might be that all continental mass was again joined in one supercontinent between roughly 600 and 550 million years ago. This hypothetical supercontinent is called Pannotia.
Unlike later supercontinents, Rodinia itself was entirely barren. It existed before life colonized dry land, and, since it predated the formation of the ozone layer, it was too exposed to ultraviolet sunlight for any organism to inhabit it. Nevertheless, its existence did significantly influence the marine life of its time.
In the Cryogenian period the Earth experienced large glaciations, and temperatures were at least as cool as today. Substantial areas of Rodinia may have been covered by glaciers or the southern polar ice cap.
Low temperatures may have been exaggerated during the early stages of continental rifting. Geothermal heating peaks in crust about to be rifted; and since warmer rocks are less dense, the crustal rocks rise up relative to their surroundings. This rising creates areas of higher altitude, where the air is cooler and ice is less likely to melt with changes in season, and it may explain the evidence of abundant glaciation in the Ediacaran period.
The eventual rifting of the continents created new oceans, and seafloor spreading, which produces warmer, less-dense oceanic lithosphere. Due to its lower density, hot oceanic lithosphere will not lie as deep as old, cool oceanic lithosphere. In periods with relatively large areas of new lithosphere, the ocean floors come up, causing the eustatic sea level to rise. The result was a greater number of shallower seas.
The increased evaporation from the larger water area of the oceans may have increased rainfall, which, in turn, increased the weathering of exposed rock. By inputting data on the ratio of stable isotopes O18 : O16 into computer models, it has been shown that in conjunction with quick-weathering of volcanic rock, this increased rainfall may have reduced greenhouse gas levels to below the threshold required to trigger the period of extreme glaciation known as ‘Snowball Earth’.
Increased volcanic activity also introduced into the marine environment biologically active nutrients, which may have played an important role in the development of the earliest animals.
(See HERE for a news item on Rodinia, dated 25 Feb 2013)
Pannotia, first described by Ian W. D. Dalziel in 1997, is a hypothetical supercontinent that may have existed from the late Neoproterozoic Pan-African orogeny, about six hundred million years ago, to the end of the Precambrian, about five hundred and fifty million years ago. It is also known as the Vendian supercontinent. After that, it split into the islands of Laurentia, Siberia and Baltica, with the main landmass, Gondwana, south of it.
About 750 million years ago (750 Ma), the previous supercontinent Rodinia rifted apart into three continents: Proto-Laurasia (which broke apart and eventually re-formed as Laurasia), the continental craton of Congo, and Proto-Gondwana (all of Gondwana except the Congo craton and Atlantica).
Proto-Laurasia rotated southward toward the South Pole. Proto-Gondwana rotated counter-clockwise. The Congo craton came between Proto-Gondwana and Proto-Laurasia about 600 Ma. This formed Pannotia. With so much landmass around the poles, evidence suggests that there were more glaciers during this time than at any other time in geologic history.
Pannotia looked like a V that faced northeast. Inside the V was an ocean that opened up during the break-up of Rodinia, the Panthalassic Ocean, an ocean that became the early Pacific Ocean. There was a mid-ocean ridge in the middle of the Panthalassic Ocean. Outside of the V was a very large ancient ocean called the Panafrican Ocean that may have surrounded Pannotia, equivalent to the future Panthalassic Ocean.
Pannotia was short-lived. The collisions that formed Pannotia were glancing collisions, and the continents composing Pannotia already had active rifting. By about 540 Ma, or only about 60 million years after Pannotia formed, Pannotia disintegrated into four continents: Laurentia, Baltica, Siberia and Gondwana. Later, altered landmasses would recombine to form the most recent supercontinent, Pangaea.
Another term for the supercontinent that is thought to have existed at the end of Neoproterozoic time is "Greater Gondwanaland", suggested by Stern in 1994. This term recognizes that the supercontinent of Gondwana, which formed at the end of the Neoproterozoic, was once part of the much larger end-Neoproterozoic supercontinent.
Euramerica (also known as Laurussia (not to be confused with Laurasia), the Old Red Continent or the Old Red Sandstone Continent) was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica, and Avalonia cratons (Caledonian orogeny). 300 million years ago in the Late Carboniferous tropical rainforests lay over the equator of Euramerica. A major, abrupt change in vegetation occurred when the climate aridified. The forest fragmented and the lycopsids which dominated these wetlands thinned out, being replaced by opportunistic ferns. There was also a great loss of amphibian diversity and simultaneously the drier climate spurred the diversification of reptiles.
Euramerica became a part of the major supercontinent Pangaea in the Permian. In the Jurassic, when Pangaea rifted into two continents, Gondwana and Laurasia, Euramerica was a part of Laurasia.
In the Cretaceous, Laurasia split into the continents of North America and Eurasia. The Laurentian craton became a part of North America while Baltica became a part of Eurasia, and Avalonia was split between the two.
Carboniferous: Climate change devastated tropical rainforests, fragmenting the forests into isolated 'islands' and causing the extinction of many plant and animal species during the Carboniferous Rainforest Collapse (CRC).
Permian: Euramerica became a part of the major supercontinent Pangaea
Jurassic: Pangaea rifted into Gondwana and Laurasia
Cretaceous: Laurasia split into the continents of North America and Eurasia.
Pangaea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras, forming about 300 million years ago and beginning to rift around 200 million years ago, before the component continents were separated into their current configurations. The single global ocean which surrounded Pangaea is accordingly named Panthalassa.
The name Pangaea is derived from Ancient Greek pan meaning "entire," and Gaia meaning "Earth." The name was coined during a 1927 symposium discussing Alfred Wegener's theory of continental drift. In his book The Origin of Continents and Oceans (Die Entstehung der Kontinente und Ozeane), first published in 1915, he postulated that before later breaking up and drifting to their present locations, all the continents had at one time formed a single supercontinent which he called the "Urkontinent".
The forming of supercontinents and their breaking up appears to have been cyclical through Earth's history. There may have been several others before Pangaea. The fourth-last supercontinent, called Columbia or Nuna, appears to have assembled in the period 2.0–1.8 Ga. Columbia/Nuna broke up and the next supercontinent, Rodinia, formed from the accretion and assembly of its fragments. Rodinia lasted from about 1.1 billion years ago (Ga) until about 750 million years ago, but its exact configuration and geodynamic history are not nearly as well understood as those of the later supercontinents, Pannotia and Pangaea.
When Rodinia broke up, it split into three pieces: the supercontinent of Proto-Laurasia, the supercontinent of Proto-Gondwana, and the smaller Congo craton. Proto-Laurasia and Proto-Gondwana were separated by the Proto-Tethys Ocean. Next Proto-Laurasia itself split apart to form the continents of Laurentia, Siberia and Baltica. Baltica moved to the east of Laurentia, and Siberia moved northeast of Laurentia. The splitting also created two new oceans, the Iapetus Ocean and Paleoasian Ocean. Most of the above masses coalesced again to form the relatively short-lived supercontinent of Pannotia. This supercontinent included large amounts of land near the poles and, near the equator, only a relatively small strip connecting the polar masses. Pannotia lasted until 540 Ma, near the beginning of the Cambrian period and then broke up, giving rise to the continents of Laurentia, Baltica, and the southern supercontinent of Gondwana.
In the Cambrian period, the continent of Laurentia, which would later become North America, sat on the equator, with three bordering oceans: the Panthalassic Ocean to the north and west, the Iapetus Ocean to the south and the Khanty Ocean to the east. In the Earliest Ordovician, around 480 Ma, the microcontinent of Avalonia – a landmass that would become the northeastern United States, Nova Scotia, and parts of current Great Britain, Iberia and the Maghreb – broke free from Gondwana and began its journey to Laurentia. Baltica, Laurentia, and Avalonia all came together by the end of the Ordovician to form a minor supercontinent called Euramerica or Laurussia, closing the Iapetus Ocean. The collision also resulted in the formation of the northern Appalachians. Siberia sat near Euramerica, with the Khanty Ocean between 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.
The second step in the formation of Pangaea was the collision of Gondwana with Euramerica. By Silurian time, 440 Ma, Baltica had already collided with Laurentia, forming Euramerica. 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 newly formed Rheic Ocean. It collided with southern Baltica in the Devonian, though this microcontinent was an underwater plate. The Iapetus Ocean's sister ocean, the Khanty Ocean, shrank as an island arc from Siberia collided with eastern Baltica (now part of Euramerica). Behind this island arc was a new ocean, the Ural Ocean.
By late Silurian time, North and South China split from Gondwana and started to head northward, shrinking the Proto-Tethys Ocean in their path and opening the new Paleo-Tethys Ocean to their south. In the Devonian Period, Gondwana itself headed towards Euramerica, causing the Rheic Ocean to shrink. In the Early Carboniferous, northwest Africa had touched the southeastern coast of Euramerica, creating the southern portion of the Appalachian Mountains, and the Meseta Mountains. South America moved northward to southern Euramerica, while the eastern portion of Gondwana (India, Antarctica and Australia) headed toward the South Pole from the equator. North and South China were on independent continents. The Kazakhstania microcontinent 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.)
Western Kazakhstania collided with Baltica in the Late Carboniferous, closing the Ural Ocean between them and the western Proto-Tethys in them (Uralian orogeny), causing the formation of not only the Ural Mountains but also 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 Appalachians and 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 China block collided with Siberia by Late Carboniferous time, completely closing the Proto-Tethys Ocean.
By Early Permian time, the Cimmerian plate split from Gondwana and headed towards Laurasia, thus closing the Paleo-Tethys Ocean, but forming a new ocean, the Tethys Ocean, in its southern end. Most of the landmasses were all in one. By the Triassic Period, Pangaea rotated a little and the Cimmerian plate was still travelling across the shrinking Paleo-Tethys, until the Middle Jurassic time. The Paleo-Tethys had closed from west to east, creating the Cimmerian Orogeny. Pangaea, which looked like a C, with the new Tethys Ocean inside the C, had rifted by the Middle Jurassic, and its deformation is explained below.
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 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 been found in only localized regions of the coasts of Brazil and West Africa.
Additional evidence for Pangaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South America and the western coast of Africa. The polar ice cap of the Carboniferous Period 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.
There were three major phases in the break-up of Pangaea. The first 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 in the west, ultimately giving rise to the supercontinents Laurasia and Gondwana. 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.
The Atlantic Ocean did not open uniformly; rifting began in the north-central Atlantic. The South Atlantic did not open until the Cretaceous when Laurasia started to rotate clockwise and moved northward with North America to the north, and Eurasia to the south. The clockwise motion of Laurasia led to the closing of the Tethys Ocean. Meanwhile, on the other side of Africa and along the adjacent margins of east Africa, Antarctica and Madagascar, new rifts were forming that would not only lead to the formation of the southwestern Indian Ocean but 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 multiple continents (Africa, South America, India, Antarctica, and 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, Madagascar and 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) a year (a plate tectonic record), closing the Tethys Ocean, while Madagascar stopped and became locked to the African Plate. New Zealand, New Caledonia and the rest of Zealandia began to separate from Australia, moving eastward toward the Pacific and opening the Coral Sea and Tasman Sea.
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 rapidly northward, just as India had done more than 40 million years before. It is currently on a collision course with eastern Asia. Both Australia and India are currently moving northeast at 5–6 centimetres (2–3 in) a year. Antarctica has been near or at the South Pole since the formation of Pangaea about 280 Ma. India started to collide with Asia beginning 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. This motion, together with decreasing atmospheric carbon dioxide concentrations, caused a rapid cooling of Antarctica and allowed glaciers to form. This glaciation eventually coalesced into the kilometres-thick ice sheets seen today. 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 Red Sea Rift and East African Rift.
Watch a simple 6-minute video explaining Pangea at:
(If their server is having problems, you might have to copy & paste the URL into your browser)
In paleogeography, Laurasia was the northernmost of two supercontinents (the other being Gondwana) that formed part of the Pangaea supercontinent from approximately 510 to 200 million years ago (Mya). It separated from Gondwana 200 to 180 Mya (the late Triassic era) during the breakup of Pangaea, drifting further north after the split.
The name combines the names of Laurentia, the name given to the North American craton, and Eurasia. As suggested by the geologic naming, Laurasia included most of the landmasses which make up today's continents of the Northern Hemisphere, chiefly Laurentia (i.e. the core North American continent), Baltica, Siberia, Kazakhstania, and the North China and East China cratons.
Although Laurasia is known as a Mesozoic phenomenon, today it is believed that the same continents that formed the later Laurasia also existed as a coherent supercontinent after the breakup of Rodinia around 1 billion years ago. To avoid confusion with the Mesozoic continent, this is referred to as Proto-Laurasia. It is believed that Laurasia did not break up again before it recombined with the southern continents to form the late Precambrian supercontinent of Pannotia, which remained until the early Cambrian. Laurasia was assembled, then broken up, due to the actions of plate tectonics, continental drift and seafloor spreading.
During the Cambrian, Laurasia was largely located in equatorial latitudes and began to break up, with North China and Siberia drifting into latitudes further north than those occupied by continents during the previous 500 million years. By the Devonian, North China was located near the Arctic Circle and it remained the northernmost land in the world during the Carboniferous Ice Age between 300 and 280 million years ago. There is no evidence, though, for any large scale Carboniferous glaciation of the northern continents. This cold period saw the re-joining of Laurentia and Baltica with the formation of the Appalachian Mountains and the vast coal deposits, which are a mainstay of the economies of such regions as West Virginia, Britain and Germany.
Siberia moved southwards and joined with Kazakhstania, a small continental region believed today to have been created during the Silurian by extensive volcanism. When these two continents joined together, Laurasia was nearly reformed, and by the beginning of the Triassic, the East China craton had rejoined the redeveloping Laurasia as it collided with Gondwana to form Pangaea. North China became, as it drifted southwards from near-Arctic latitudes, the last continent to join with Pangaea.
Around 200 million years ago, Pangaea started to break up. Between eastern North America and northwest Africa, a new ocean formed - the Atlantic Ocean, even though Greenland (attached to North America) and Europe were still joined together. The separation of Europe and Greenland occurred around 55 million years ago (at the end of the Paleocene). Laurasia finally divided into the continents after which it is named: Laurentia (now North America) and Eurasia (excluding India).
In paleogeography, Gondwana (originally Gondwanaland) is the name given to the more southerly of two supercontinents (the other being Laurasia) which were part of the Pangaea supercontinent that existed from approximately 510 to 180 million years ago (Mya). Gondwana is believed to have sutured between ca. 570 and 510 Mya, thus joining East Gondwana to West Gondwana. It separated from Laurasia 200-180 Mya (the mid-Mesozoic era) during the breakup of Pangaea, drifting farther south after the split.
Gondwana included most of the landmasses in today's Southern Hemisphere, including Antarctica, South America, Africa, Madagascar and the Australian continent, as well as the Arabian Peninsula and the Indian subcontinent, which have now moved entirely into the Northern Hemisphere.
The continent of Gondwana was named by Austrian scientist Eduard Suess, after the Gondwana region of central northern India (from Sanskrit gondavana "forest of the Gonds"), from which the Gondwana sedimentary sequences (Permian-Triassic) are also described.
The adjective Gondwanan is in common use in biogeography when referring to patterns of distribution of living organisms, typically when the organisms are restricted to two or more of the now-discontinuous regions that were once part of Gondwana, including the Antarctic flora. For example, the Proteaceae family of plants known only from southern South America, South Africa and Australia, is considered to have a "Gondwanan distribution". This pattern is often considered to indicate an archaic, or relict, lineage.
The assembly of Gondwana was a protracted process. Several orogenies led to its final amalgamation 550–500 Mya at the end of the Ediacaran, and into the Cambrian. These include the Brasiliano Orogeny, the East African Orogeny, the Malagasy Orogeny, and the Kuunga Orogeny. The final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval the Cambrian explosion occurred.
Gondwana was formed from the following earlier continents and microcontinents, among others, colliding in the following orogenies:
· Azania: much of central Madagascar, the Horn of Africa and parts of Yemen and Arabia. (Named by Collins and Pisarevsky (2005): "Azania" was a Greek name for the East African coast.);
· The Congo–Tanzania–Bangweulu Block of central Africa;
· Neoproterozoic India: India, the Antongil Block in far eastern Madagascar, the Seychelles, and the Napier and Rayner Complexes in East Antarctica;
· The Australia/Mawson continent: Australia west of Adelaide and a large extension into East Antarctica;
· Other blocks which helped to form Argentina and some surrounding regions, including a piece transferred from Laurentia when the west edge of Gondwana scraped against southeast Laurentia in the Ordovician. This is the Famatinian block (named after Famatina in northwest Argentina) and it formerly continued the line of the Appalachians southwards.
One of the major sites of Gondwanan amalgamation was the East African Orogeny (Stern, 1994), where these two major orogenies are superimposed. The East African Orogeny at ~650–630 Mya affected a large part of Arabia, north-eastern Africa, East Africa and Madagascar. Collins and Windley (2002) propose that in this orogeny, Azania collided with the Congo–Tanzania–Bangweulu Block.
The later Malagasy orogeny at ~550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt.
At the same time, in the Kuunga Orogeny Neoproterozoic India collided with the Australia/Mawson continent.
Other large continental masses, including the core cratons of North America (the Canadian Shield or Laurentia), Europe (Baltica), and Siberia, were added over time to form the supercontinent Pangaea by Permian time. When Pangea broke up (mostly during the Jurassic), two large masses, Gondwana and Laurasia, were formed. The re-formed Gondwanan continent was not precisely the same as that which had existed before Pangaea formed; for example, most of Florida and southern Georgia and Alabama is underlain by rocks that were originally part of Gondwana but that were left attached to North America when Pangaea broke apart.
Gondwana began to break up in the early Jurassic (about 184 Mya) accompanied by massive eruptions of basalt lava, as East Gondwana, comprising Antarctica, Madagascar, India and Australia, began to separate from Africa. South America began to drift slowly westward from Africa as the South Atlantic Ocean opened, beginning about 130 Mya during the Early Cretaceous, and resulting in open marine conditions by 110 Mya. East Gondwana then began to separate about 120 Mya when India began to move northward.
The Madagascar block, and a narrow remnant microcontinent presently occupied by the Seychelles Islands, were broken off India; elements of this breakup nearly coincide with the Cretaceous–Paleogene extinction event. The India–Madagascar–Seychelles separations appear to coincide with the eruption of the Deccan basalts, whose eruption site may survive as the Réunion hotspot.
Australia began to separate from Antarctica perhaps 80 Mya (Late Cretaceous), but sea-floor spreading between them became most active about 40 Mya during the Eocene epoch of the Paleogene Period.
New Zealand probably separated from Antarctica between 130 and 85 Mya.
As the age of mammals commenced, the continent of Australia-New Guinea began gradually to separate and move north (55 Mya), rotating about its axis to begin with, and thus retaining some connection with the remainder of Gondwana for about 10 million years.
About 45 Mya, the Indian Plate collided with Asia, buckling the crust and forming the Himalayas. At about the same time, the southernmost part of Australia (modern Tasmania) finally separated from Antarctica, letting ocean currents flow between the two continents for the first time. Antarctica became cooler and Australia became drier because ocean currents circling Antarctica were no longer directed around northern Australia into the subtropics.
The separation of South America from West Antarctica some time during the Oligocene, perhaps 30 Mya, also caused climate changes. Immediately before this separation, South America and East Antarctica were not connected directly. However, the many microplates of the Antarctic Peninsula remained near southern South America, acting as "stepping stones" and allowing continued biological interchange and stopped oceanic current circulation. When the Drake Passage opened, there was no longer a barrier to force the cold waters of the Southern Ocean north to be exchanged with warmer tropical water. Instead, a cold circumpolar current developed and Antarctica became what it is today: a frigid continent that locks up much of the world's fresh water as ice. Sea temperatures dropped by almost 10°C, and the global climate became much colder.
By about 15 Mya, the collision between New Guinea (on the leading edge of the Australian Plate) and the southwestern part of the Pacific Plate pushed up the New Guinea Highlands, causing a rain shadow effect which drastically changed weather patterns in Australia, drying it out.
Later, South America was connected to North America via the Isthmus of Panama, cutting off a circulation of warm water and thereby creating the Arctic, as well as allowing the Great American Faunal Interchange.
The Red Sea and East African Rift are modern examples of the continuing dismemberment of Gondwana.