Oxygen may have been present on Earth 300 million years before it was breathed into the atmosphere, scientists concluded from a new research.
Researchers from Massachusetts Institute of Technology discovered evidence that small aerobic organisms could have evolved to survive on extremely low levels of the gas in undersea "oxygen oases," keeping a low profile in the oceans before its debut in the atmosphere.
Former MIT graduate student Jacob Waldbauer, together with Professor of Geobiology Roger Summons and Dianne Newman, formerly of MIT's Department of Biology and now at the California Institute of Technology, found through lab experiments that yeast has the ability to produce key oxygen-dependent compounds, even with only minuscule puffs of the gas.
Early ancestors of yeast, therefore, could have worked even 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 researchers suggested that oxygen may have existed 300 million years before spiking in the atmosphere, and that oxygen may have been sufficient enough to feed aerobic, sterol-producing organisms.
Looking to 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 oxygen's presence, yeast could take up sterol from the medium without creating any from scratch. When tiny amounts of oxygen was 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.
"This shows us that yeast, and presumably many or all eukaryotes, can make sterols with very, very low concentrations of oxygen," says Alex Sessions, professor of geobiology at Caltech. "The limit that they find is much lower than I - and I suspect most microbiologists - would have expected."
"The time at which oxygen became an integral factor in cellular metabolism was a pivotal point in Earth history," says Summons. "The fact that you could have oxygen-dependent biosynthesis very early on in the Earth's history has significant implications."
Their findings were published in the Proceedings of the National Academy of Sciences.