Models for the thermal evolution of the Earth together with evidence from seismology and studies of mantle derived xenoliths suggest that surviving Archean lithosphere has a mantle part that is chemically distinct from ‘normal’ upper mantle material elsewhere. The distinctive chemical composition was a key to its preservation, being necessary during the Archean to protect the lithosphere from widespread melting at its base. However, a major change takes place once the mantle cools to the point that the rheological properties of ‘normal’ mantle are sufficient to produce a thickness of lithosphere such that the geotherm no longer intersects the mantle solidus. This transition, which seems to have taken place at or near the Archean-Proterozoic boundary, should be seen in the seismic velocities under Proterozoic areas being different from those under Archean cratons, and more like that under old ocean basins. The transition should also be seen as a major time of crustal stabilization, for which there is evidence at least from North America, as well as a time of drastic reduction in the rate of crustal recycling. The Nd isotopic evolution of the mantle can be interpreted in terms of just such a reduction in recycling taking place near the beginning of the Proterozoic.
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Frank M. Richter (1988) studied this question.