August 16, 2011

Oxygen May Have Been Present On An Earlier Earth

New research suggests oxygen may have been made on Earth hundreds of millions of years before its debut in the atmosphere.

MIT researchers found evidence that tiny aerobic organisms may have evolved to survive on extremely low levels of the gas in these undersea oases.

Former MIT graduate student Jacob Waldbauer found while working with colleagues that yeast is able to produce key oxygen-dependent compounds, even with only minuscule puffs of the gas.

The research suggests that early ancestors of yeast could have been similarly resourceful, working with whatever small amounts of oxygen may have been circulating in the oceans before the gas was detectable in the atmosphere.

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

Waldbauer and colleagues believe that oxygen was present on Earth 300 million years before it spiked in the atmosphere.  They say that this oxygen may have even been sufficient enough to feed organisms.

The researchers looked at modern yeast as a model to test their theory.  Yeast naturally uses oxygen in combination with sugars, to synthesize ergosterol, which is its primary sterol. 

The team set up an experiment to find the lowest level of oxygen yeast can consume. 

Waldbauer's yeast cells grew with a mixture of essential ingredients, including ergosterol as well as glucose labeled with carbon-13. 

The team found that when yeast was given tiny amounts of oxygen, it began using it in combination with glucose to produce its own sterols.

The scientists found that yeast are able to make steroids using vanishingly small, nano molar concentrations of oxygen, which supports the theory that oxygen may have been around on Earth before the gas made an appearance in the atmosphere.

"This shows us that yeast, and presumably many or all eukaryotes, can make sterols with very, very low concentrations of oxygen," Alex Sessions, professor of geobiology at Caltech, who was not involved in this research, said in a press release. "The limit that they find is much lower than I "” and I suspect most microbiologists "” would have expected."

The team said oxygen production and consumption may have occurred in the oceans for hundreds of millions of years before the atmosphere saw a trace of the gas.

They said blue-green algae living at the ocean surface evolved the ability to produce oxygen through sunlight in a process known as oxygenic photosynthesis. 

"We know all kinds of biology happens without any O2 at all," Waldbauer, now a postdoc at Caltech, said in a press release. "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."

The research was published in the Proceedings of the National Academy of Sciences (PNAS) last week.


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