Tectonic Evolution of the Earth

Geoffrey F. Davies 1

1 Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia

The dynamical modelling reported above has substantial implications for the tectonic evolution of the Earth. The thinner early oceanic crust would enhance the viability of plate tectonics, which in turn would provide a straightforward mechanism for cooling the mantle. Such a mechanism has been lacking, as the previously expected thick oceanic crust would tend to inhibit plate tectonics and mantle cooling. This is because oceanic crust is less dense than the mantle and so tends to inhibit or block subduction of plates. The implication that plate tectonics may have been viable very early in the Earth's history was greeted with considerable interest at a Penrose conference on “When Did Plate Tectonics Begin”, which is a controversial question. A jointly authored conference paper is in preparation.

A further implication is that, although cooling of the mantle by plate tectonics is more viable, it is rate-limited by the thickness of the crust. The net result is that the mantle tends to be buffered in a hotter state than it would with unimpeded plates. It is possible there would be a transition, involving heightened volcanic and tectonic activity, into the present, cooler state once radioactive heat generation declined to a threshold level. This implication is still conjectural, but has also generated interest for its potential explanation of the episodicity of the record of tectonic activity. A paper has been contributed to a volume on “The Earth's Oldest Rocks”.