Supercontinent Cycle

The supercontinent cycle describes 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 last supercontinent, Pangaea, formed about 300 million years ago. The previous supercontinent, Pannotia, formed about 600 million years ago, and its dispersal formed the fragments that ultimately collided to form Pangaea. But beyond this the time span between supercontinents becomes more irregular. For example, the supercontinent before Pannotia, Rodinia, existed ~1.25 billion to ~750 million years ago - a mere 150 million years before Pannotia. The supercontinent before this was Columbia: ~1.8 to 1.5 billion years ago. And before this was Kenorland: ~2.7 to ~2.1 billion years ago. The first supercontinents were Ur (existed ~3 billion years ago) and Vaalbara (~3.6 to ~2.8 billion years ago).

Analysis of the composition of mineral inclusions inside ancient diamonds suggests that the cycle of supercontinental formation and breakup began roughly 3.0 billion years ago. Before 3.2 billion years ago only diamonds with peridotitic compositions (commonly found in the Earth's mantle) formed whereas after 3.0 billion years ago eclogitic diamonds (rocks from the Earth's surface crust) became prevalent. This is thought to be due to the introduction of eclogite into subcontinental diamond-forming fluids via subduction and continental collision.

The hypothetical supercontinent cycle is, in some ways, the complement to the Wilson cycle. The latter is named after plate tectonics pioneer J. Tuzo Wilson and describes the periodic opening and closing of ocean basins. Because the oldest seafloor is only 170 million years old, whereas the oldest bit of continental crust goes back to 4 billion years or more, it makes sense to emphasize the much longer record of the planetary pulse that is recorded in the continents.