New research suggests that oxygen may have been present in Earth's ancient oceans millions of years before it was breathed into the atmosphere.

Researchers from Massachusetts Institute of Technology (MIT) suggest that oxygen may have been laying low in what they call "oxygen oases" in the oceans, long before the Great Oxidation Event, or GOE. They found evidence that tiny aerobic organisms could have evolved to survive on extremely low levels of oxygen in undersea oases.

Former MIT graduate student, Jacob Waldbauer, along with Roger Summons, Professor of Geobiology, and Dianne Newman, formerly with the Department of Biology, MIT, and now at the California Institute of Technology, performed laboratory experiments on yeast, which can survive without oxygen.

They found that yeast has the ability to produce key oxygen-dependent compounds with just little puffs of the gas. With this outcome, they proposed that early ancestors of yeast could have been similarly resourceful, working with tiny amounts of oxygen in the oceans, before the "Great Oxidation Event" nearly 2.3 billion years ago when oxygen was detectable in the atmosphere.

The findings were published in the Proceedings of the National Academy of Sciences.

Looking at modern yeast as a model to test their theory, the scientists set up an experiment to identify the spot at which yeast switches from anaerobic to aerobic activity. Without the presence of oxygen, yeast could take up sterol from the medium without creating any from scratch. When tiny amounts of oxygen were pumped in, yeast started to use O2 in combination with glucose to produce its own sterols. Even vanishingly small, nanomolar concentrations of oxygen were sufficient for yeast to make steroids.

The scientists found that yeast is able to make steroids using vanishingly small, nanomolar concentrations of oxygen, supporting the theory that oxygen — and its producers and consumers — may have indeed been around long before it made an appearance in the atmosphere.

"We know all kinds of biology happens without any O2 at all. But it's quite possible there was a vigorous cycle of O2 happening in some places, and other places it might have been completely absent," said Waldbauer, the Study co-author, in an MIT press release.

"The time at which oxygen became an integral factor in cellular metabolism was a pivotal point in Earth history. The fact that you could have oxygen-dependent biosynthesis very early on in the Earth's history has significant implications," said Summons in a press release.

Waldbauer and his colleagues suggest that oxygen may have been actually present on Earth 300 million years before it appeared in the atmosphere, but at such low concentrations that the gas wouldn't have left much of a trace in the rock record. Even at such low levels, this oxygen may have been adequate enough to feed aerobic, sterol-producing organisms.

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