Reinhard: Exactly how much oxygen was or wasn't around when this transition took place and how much oxygen really was there in the atmosphere?
Narrator: UC Riverside graduate student Chris Reinhard was part of a team that found evidence that the effects of biological oxygen production began in the oceans at least 100 million years before the accumulation of significant quantities of atmospheric oxygen.
Reinhard: This is not a new notion. There was some research published in 1999 that suggested that oxygen production had evolved two or three hundred million years before the rise in atmospheric oxygen. So, this idea of oxygen production has sort of been reinvigorated by the work that we're doing now.
Narrator: For Science Today, I'm Larissa Branin.