Supercontinent

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 qualifies as a supercontinent today.

History
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.

The supercontinent cycle theory postulates that supercontinents form in cycles, coming together and breaking apart again through plate tectonics, very roughly about every 250 million years.

Geology
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 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.