Abstract
The episodicity of impacts on the Moon, which must take place also on the Earth, appears to be accompanied by orogenic episodes on the Earth. Seven of eleven episodes of major impacts in the Precambrian era were followed by orogenic events with a time lag of about 100Myr. A possible scenario explaining the coincidence is as follows. A shock wave from a major impact might have caused the spinel-post-spinel transformation in megaliths accumlated around the 670km discontinuity and/or huge melting in the upper mantle. The gravitational instabilities of the megaliths or the melted parts brought about down-welling or up-welling superplumes, respectively. Then rapid mantle convections induced by the superplumes produced global tectonics such as a formation or breakup of a supercontinent.
