The Boring Billion

Also see: Endosymbiotic Theory

One of the real mysteries of deep time on Earth is the apparent stalling of evolution, in general, and of eukaryotes, in particular, during the early proterozoic. Weight of the evidence suggests evolution was in stasis for some billion years despite an atmosphere that had been being oxygenated for a long time through photosynthesis by both prokaryotic and eukaryotic organisms (as early as 3500 mliion years ago). Why didn't eukaryotic life truly take off with their new metabolic engines that used oxygen as a superfuel? Why was their emergence as macroscopic multicellular animals delayed until the Ediacaran, some 635 million years ago (mya)? Why was the Cambrian explosion postponed until until some 521 mya? There are so many competing hypotheses, all scientifically plausible, regarding the boring billion, that perhaps it would be better named: "the equivocal billion.

Wrapped up in the mystery of the boring billion is the so-called Great Oxygenation Event (GOE), sometimes also called the Oxygen Catastrophe. The process leading to the GOE event is believed to have begun in the Paleoproterozoic some 2300 mya when free oxygen began to build in the atmosphere.