The outer shell of the Earth is broken up into 12 major plates and a few smaller ones. The boundaries between those plates, according to plate tectonic theory, come in three varieties: midocean ridges, where plates diverge; deep-sea trenches and other subduction zones, where two plates converge and one dives under the other; and transform faults like the San Andreas, where plates slide past each other. In 1995, however, this neat scheme stood for some revision: the 12 major plates became 13, and a new type of plate boundary--convergent and divergent at the same time--was discovered in the Indian Ocean.
According to geophysicist James Cochran of the Lamont-Doherty Earth Observatory and his colleagues, India and Australia are going their separate ways: the giant Indo-Australian plate that was once thought to carry both has actually been breaking apart for roughly seven and a half million years. The most likely cause was ...
