Narrator:       This is Science Today. Scientists have known that about 2.4 billion years ago, the Earth's atmosphere experienced a dramatic change when oxygen levels rose sharply. Less clear has been just when biological oxygen production emerged, and whether it could have altered the chemistry of the ocean and atmosphere prior to this sharp change. A University of California, Riverside-led team of geoscientists set out to get some answers.

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.