No. 63: May-Jun 1989
This long article concludes with an intriguing snippet.
"Plate tectonic processes circulate the entire oceanic crust back into the mantle every 100 million years. Ero sion also removes part of the continental crust, and some of the eroded material may eventually find its way to deep oceanic trenches, where it is also returned to the mantle. This implies that at any given time only about 10% of the crust is at the surface. Much of the continental crust, however, is more than half the age of the earth, so one can infer this part has not recirculated recently."
(Anderson, Don L.; "Where on Earth Is the Crust?" Physics Today, 42:38, 1989.)
Comment. The machinations of plate tectonics, therefore, may well be responsi ble for missing sections of the geologi cal column and fossil record.