In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia[1] qualifies as a supercontinent today.
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Most commonly, paleogeographers employ the term supercontinent to refer to a single landmass consisting of all the modern continents. The earliest known supercontinent was Vaalbara. It formed from proto-continents and was a supercontinent by 3.1 billion years ago (3.1 Ga). Vaalbara broke up ~2.8 Ga. The supercontinent Kenorland was formed ~2.7 Ga and then broke sometime after 2.5 Ga into the proto-continent cratons called Laurentia, Baltica, Australia, and Kalahari. The supercontinent Columbia formed and broke up during a period of 1.8 to 1.5 billion years (1.8-1.5 Ga) ago.
The supercontinent Rodinia broke up roughly 750 million years ago. One of the fragments included large parts of the continents now located in the southern hemisphere. Plate tectonics brought the fragments of Rodinia back together in a different configuration during the late Paleozoic era, forming the best-known supercontinent, Pangaea. Pangaea subsequently broke up into the northern and southern supercontinents, Laurasia and Gondwana.
Modern studies [which?] have suggested that supercontinents form in cycles, coming together and breaking apart again through plate tectonics, very roughly about every 250 million years.
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 plate tectonics makes them re-join after travelling around the planet, or if they move apart and then back together again.
In other areas of study such as history and geography, land masses connected with an isthmus are also considered supercontinents or just continents, such as the Americas. Some historians call the combined land mass of Africa and Eurasia the supercontinent Afro-Eurasia.
In reverse-chronological order (stratolithic order) comprising nearly all land at the time.