ARCHEAN EON

3.9-2.5 Ga

 

The Archean Earth

Image courtesy of http://www.cotf.edu/ete/modules/msese/earthsysflr/cambrian.html

The Archean Eon represents a fascinating segment of Earth' s history. The first signs of stable continental crust and  life emerged between 3.5-4.0 Ga. The Archean Eon is notable for the development of continental blocks and permobile belts. Permobile belts refer to tectonically active zones characterized by high geothermal gradient, rapid convection and unstable crust. Archean tectonics were marked by a lack of stable cratons--essentially no large masses of continental crust had accumulated 3.9 Ga. Instead, thin lithospheric material of microcontinents and volcanic arcs collided, small "marginal" ocean basins opened and were later subducted. Gradually, the sequence of microcontinent collisions produced larger cratonic blocks. The initial assembly of Archean cratons produced a supercontinent named "Ur "

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