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USGS CMG InfoBank: Early Crust

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Comment: 03:48 - 05:05 (01:17)
Source: Annenberg/CPB Resources - Earth Revealed - 7. Mountain Building
Keywords: water, atmosphere, "oceanic crust", "convergent plate", "island arc", "sea floor spreading", "convective cell", "continental crust", supercontinent, accretion, plate, "upper mantle", "Gary Ernst"

Our transcription: Initially, in the early Earth, the crust of the Earth must have been principally oceanic crust surmounted by a thin veneer of water and a very dense atmosphere.
Gradually, due to convergent plate motion, they were probably pretty small thin platelets back in early times, we're talking three, four billion years ago, small island arcs began to form along and above convergent plate junctions due to the rise of melt from the down-going slab up into these primitive arcs.
As those island arcs formed they were swept together by this continual sea floor spreading process; probably involved a lot of small rapidly overturning convective cells in the upper mantle.
So very rapid growth accompanied the early Earth, and as these accreted together they formed enlarging eventually supercontinental assemblies.
Those assemblies were annealed over time, and gradually they formed relatively larger plates capped by continental crust.
The continental crust itself is an amalgam of these smaller island arcs, which had been all swept together.

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