Without the presence of oxygen, yeast could take up sterol from the medium without creating any from scratch. 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.
"The time at which oxygen became an integral factor in cellular metabolism was a pivotal point in Earth history. Even at such low levels, this oxygen may have been adequate enough to feed aerobic, sterol-producing organisms.
Oxygen may have been present in Earth's ancient oceans, hundreds of millions of years before it began to mingle with the atmosphere.
MIT researchers say it's possible that oxygen was present in so-called oxygen oases in the oceans, long before what's described as the "Great Oxidation Event" some 2.3 billion years ago loosed the life-giving element into the Earth's atmosphere. The researchers conducted lab experiments which turned up evidence suggesting that aerobic organisms may have been able to survive on very low levels of oxygen in these undersea oases. "The fact that you could have oxygen-dependent biosynthesis very early on in the Earth's history has significant implications."
Oxygen may have been sustaining life in Earth's oceans long before there was any trace of it in the atmosphere.
Yeast — an organism that can survive with or without oxygen — is able to produce key oxygen-dependent compounds, even with only miniscule puffs of the gas, they've discovered.
"The time at which oxygen became an integral factor in cellular metabolism was a pivotal point in Earth history," says Professor of Geobiology Roger Summons.