Supercontinent cycle

The supercontinent cycle is the quasi-periodic aggregation and dispersal of Earth's continental crust. There are varying opinions as to whether the amount of continental crust is increasing, decreasing, or staying about the same, but it is agreed that the Earth's crust is constantly being reconfigured. One complete supercontinent cycle is said to take 300 to 500 million years. Continental collision makes fewer and larger continents while rifting makes more and smaller continents.

The most recent supercontinent, Pangaea, formed about 300 million years ago. There are two different views on the history of earlier supercontinents. The first proposes a series of supercontinents: Vaalbara (c. 3.6 to c. 2.8 billion years ago); Ur (c. 3 billion years ago); Kenorland (c. 2.7 to 2.1 billion years ago); Columbia (c. 1.8 to 1.5 billion years ago); Rodinia (c. 1.25 billion to 750 million years ago); and Pannotia (c. 600 million years ago), whose dispersal produced the fragments that ultimately collided to form Pangaea.

The second view (Protopangea-Paleopangea), based on both palaeomagnetic and geological evidence, is that supercontinent cycles did not occur before about 0.6 Ga (during the Ediacaran Period). Instead, the continental crust comprised a single supercontinent from about 2.7 Ga (Gigaanum, or "billion years ago") until it broke up for the first time, somewhere around 0.6 Ga. This reconstruction is based on the observation that if only small peripheral modifications are made to the primary reconstruction, the data show that the palaeomagnetic poles converged to quasi-static positions for long intervals between about 2.7–2.2, 1.5–1.25 and 0.75–0.6 Ga. During the intervening periods, the poles appear to have conformed to a unified apparent polar wander path. Thus the paleomagnetic data are adequately explained by the existence of a single Protopangea–Paleopangea supercontinent with prolonged quasi-integrity. The prolonged duration of this supercontinent could be explained by the operation of lid tectonics (comparable to the tectonics operating on Mars and Venus) during Precambrian times, as opposed to the plate tectonics seen on the contemporary Earth.

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