What triggered the Cambrian Explosion?
Almost all of today’s animal body types evolved in a single period less than ten million years long. This “explosion” of diversity occurred with seemingly random timing in a period tens of millions of years long. The abruptness of the Cambrian Explosion was a severe puzzle to Darwin, and has remained troubling ever since. Why did the Cambrian Explosion happen when it did? If it was so abrupt–just waiting to happen–why didn’t it happen earlier? Chris Phoenix thinks he knows the answer. 585 million years ago (MYA), the earth was heavily glaciated, and life (as far as we know) had not progressed past the single-celled stage. By 575 MYA, the first multicellular fossils have been found. But the Cambrian Explosion waited until about 545 MYA. There were, of course, several enabling factors, such as the retreat of glaciation, the increasing oxygen content of the atmosphere, and the gradual complexification of organisms. But all of these were slow processes, or else predated the Cambrian Expl
