I get the Geological Society of America's monthly GSA Connection newsletter, and it's almost always good. But I have to bust them for promoting a good site's poor page. The site, named as a resource in this month's newsletter, is the University of California Museum of Paleontology site, an excellent source for anything connected with fossils and evolution. But its page on plate tectonics is old and not fully correct. It repeats a couple of long outmoded ideas. One is that the plates of the lithosphere are moved about by convection currents in the underlying mantle, like porridge on a stove. Not so: it is the plates, cooling and sinking at subduction zones, that stir the mantle instead. (This is one of the most common myths of plate tectonics.) The other is that lava comes from the asthenosphere, the soft layer of rock beneath the plates, because of its heat. Not so: it is water injected into the mantle by subducting plates that causes the overlying rock to melt, not extra heat. Both of these mistaken notions have lived on in textbooks because they seem to be common sense. But plate tectonics is a living field, and the version it started out with 40 years ago has been superseded by surprising science.

This page is a contribution to Accretionary Wedge #5