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SupercontinentA supercontinent, in geology, is a land mass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that forms Eurasia qualifies as a supercontinent today. In other areas of study such as history and geography, land masses connected with an isthmus are also considered a supercontinent or just a continent, such as the Americas. Some historians call the combined land mass of Africa and Eurasia the supercontinent Africa-Eurasia, which is not a geological supercontinent though. Most commonly, paleogeographers employ the term supercontinent to refer to a landmass consisting of all the modern continents, of which the most familiar example is Pangaea (Greek for all lands). For the history and break-up of that supercontinent, see Pangaea and its successors Laurasia and Gondwana. The supercontinent Rodinia broke up roughly 750 million years ago. One of the fragments included large parts of the modern southern hemisphere continents. Continental drift then brought the fragments together in a different configuration, resulting in another supercontinent, Pangaea, forming in the late Paleozoic. Pangaea broke up into the northern and southern supercontinents, Laurasia and Gondwana. Recently Drs. John J. Rogers and M. Santosh have proposed the existence of a yet older supercontinent, Columbia, that was formed and broken up during a period of 1.8 to 1.5 billion years (1.8-1.5 Ga) ago. Modern studies have suggested that supercontinents form in cycles, coming together and breaking apart again, through plate tectonics, very roughly about every 250 million years. Before we can be sure of this, we need to pass through a few more of these cycles. Supercontinents block the flow of heat from the Earth's interior, and thus cause the asthenosphere to overheat. Eventually, the lithosphere will begin to dome upward and crack, magma will then rise, and the fragments will be pushed apart. It is currently a matter of some debate as to how the supercontinents reform, whether or not continental drift makes them re-join after travelling around the planet, or if they drift apart and then back together. Partial (incomplete) List of major past supercontinents Partial (incomplete) list of supercontinents in reverse-chronological order (stratolithic order) comprising nearly all land at the time - Pangaea Ultima (~250 – ~400 million years from now)
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- Pangaea (~300 – ~180 million years ago)
- Pannotia (~600 – ~540 million years ago)
- Rodinia (~1.1 – ~750 million years ago)
- Columbia (~1.8–1.5 Ga ago)
- Kenorland (~2.45 – ~2.10 Ga ago)
- Ur (~3 Ga ago, though probably not a supercontinent; but still however, the earliest known continent. Ur, however, was probably the largest, perhaps even the only continent three billion years ago, so one can argue that Ur was a supercontinent for its time, even if it was smaller than Australia is today)
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