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article imageHow Amasia, Earth's next supercontinent will form

By JohnThomas Didymus     Feb 12, 2012 in Science
Supercontinents are land masses formed by merging of two or more continental cores. The Earth, in the geologic ages, has had several supercontinents. Geologists believe the next supercontinent will be Amasia, a merging of the Americas and Asia.
The best known supercontinent that formed in geologic ages is Pangaea . It was formed 300 million years ago and began breaking up 200 million years ago. The components formed the continents as we know them today.
The other well known supercontinent that formed and broke up in the geologic ages was Gondwana, the southernmost of two supercontinents that formed about 510 to 180 million years ago. Gondwana included most of the landmasses in today's Southern Hemisphere, including Antarctica, South America, Africa, Madagascar, the Australian continent, the Arabian Peninsula and the Indian subcontinent.
Supercontinent Amasia
According to Discovery News, the term Amasia was first coined by Harvard University geologist Paul Hoffman. Since then two dominant theories of how Amasia will form have emerged. Both predict the continents will converge along the equator, but differ on details:
According to geologists, new supercontinents may form in two ways, by introversion or by extroversion. When a new supercontinent forms on top of a previous one the formation processs is called introversion, but when a new continent forms on the other side of the planet relative to the previous, the process is called extroversion.
In the introversion model, it is thought that the oceanic plate that formed between the continents when the supercontinent Pangaea broke up has stopped spreading out and thus the continents may drift back together and form a new configuration of continents. In the extroversion model, the oceanic plates keep spreading out causing them to meet up with each other on the other side of the planet and merge to form a new supercontinental configuration of the continents.
How Amasia will be formed according to Mitchell et al
Recently, Yale University geology and geophysics professor David Evan, along with graduate students Taylor Kilian and Ross N. Mitchell, proposed that Amasia might emerge away from its predecessor Pangaea in the Arctic region rather than along the equator. When a new supercontinent emerges sideways from the previous the process is called orthoversion.The orthoversion model of supercontinent formation proposed by Mitchell and his colleagues says new supercontinents may form sideways from previous ones.
When Pangaea broke up, its edges were subducted (that is plunged downward) into the Earth. The subduction zone coincides with the area of the Pacific Ring of Fire where major earthquakes and volcanic eruptions occur today. According to the orthoversion model, the subduction zone around a previous supercontinent channels the drift of its former components. Consequently, the present continents will drift either north or south around the Pacific Ring of Fire.
Mitchell and his colleagues suggested the continents will drift north and merge at the Arctic region to form Amasia because the Caribbean Sea separating North and South America, and the Arctic Ocean separating the Americas and Asia do not appear permanent geological formations.
The New York Times reports Mitchell said:“The fusion of North and South America together will close the Caribbean Sea and meet Eurasia at the present-day North Pole...And Australia is moving north, and would probably snuggle to join Asia somewhere between India and Japan." quotes Mitchell, saying: “After those water bodies [Carribian sea and the Artic Ocean] close, we’re on our way to the next supercontinent. You’d have the Americas meeting Eurasia practically at the North Pole.”
Test of hypothesis
To test their suggestion, the researchers tried to see which of the alternative Plate Tectonics drift theories best matched available data on how supercontinents emerge. They conducted the test using data from formation of Panagaea and Rodinia which formed 750 million and 1.1 billion years ago. They also used available data for formation of Nuna which existed between 1.5 billion to 1.8 billion years ago.
From their analysis which included an assessment of the effects of the Earth's magnetic field on alignment of magnetic minerals in ancient rocks, the researchers concluded that Pangaea did not form by introversion or extroversion but by orthoversion from Rodinia. They found also that Rodinia, in turn, emerged by orthoversion from Nuna. They, therefore, concluded that new supercontinents form by orthoversion and not by intro- or extroversion as was previously believed.
More questions on Plate Tectonics theory of continental drift
Fox News reports Mitchell said, "Now that we have a clear picture of what the supercontinent cycle actually looks like, we can begin to answer the questions of why the supercontinent cycle operates as it does. Why a supercontinent breaks apart remains an unanswered question."
Scientists are also uncertain when Amasia will form. According to Mitchell, it is "difficult to answer, because the supercontinent cycle is not as regular as the seasonal cycle, for example, but we can get a clue from Earth's history — the cycle is speeding up, such that the recurrence interval between successive supercontinents has become less and less. Knowing that Pangea formed 300 million years ago, we can predict a range of Amasia ages from 50 to 200 million years from now."
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