In the Archean tectonic regime, the time available for oceanic lithosphere to cool on its journey from ridge to convergent plate boundary was far less than at present. Under these conditions, only an inherently dense lithosphere could have acquired the negative buoyancy necessary for it to subduct. At this time, plate tectonics could have operated only if (1) the oceanic crust was rich in komatiite lava, and (2) the thickness of this crust was not much greater than the thickness of modern oceanic crust.

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