Wanderings
The Earth formed about 4.6 billion years ago. As it cooled the lithosphere, consisting of the crust and the rigid uppermost part of the mantle solidified. The lithosphere rides on the asthenosphere, which is also solid but can flow like a liquid on geological time scales. The lithosphere is broken up into tectonic plates, which slowly move in relation to one another at speeds of 50–100 mm annually, colliding, combining into continents, splitting and drifting apart to form new continental configurations.
It is difficult to reconstruct the early wanderings of the West African Craton, but around 1,100 million years ago it seems to have been one of the cratons that came together to form Rodinia, a supercontinent. At that time, the Congo Craton lay to the west of the Amazonia Craton, and the West African Craton lay to the south of them (rotated about 180°, they retain this relative configuration.)
Around 750 million years ago Rodinia rifted apart into three continents: Proto-Laurasia, the Congo craton and Proto-Gondwana. The West African Craton may then have combined with other cratons to form Pannotia, a hypothetical supercontinent that existed from the Pan-African orogeny about 600 million years ago to the end of the Precambrian about 540 million years ago. Later it became part of Gondwana, and later still part of Pangaea, the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before North and South America separated from Eurasia and Africa and the continents started to drift towards their current configuration.
Read more about this topic: West African Craton
Famous quotes containing the word wanderings:
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