The study in the journal Nature Geoscience indicates Earth's atmosphere transitioned between an oxygen-rich environment and a thick methane hydrocarbon haze similar to what is now seen on the Saturnian moon Titan.
The work by scientists including Dr Aubrey Zerkle from the University of Newcastle in the United Kingdom, analyzed marine sediments deposited in the Campbellrand-Malmani carbonate platform in South Africa's Ghaap Group.
The platform is one of the oldest on Earth with rocks dating back to between 2.65 and 2.5 billion years ago.
The analyses allowed Zerkle and colleagues to reconstruct the ocean and atmospheric chemistry of the period, finding evidence of oxygen production by microbes.
They also found carbon and sulfur isotopes indicating the oxygen was made in a reduced atmosphere that was periodically rich in methane.
Zerkle and colleagues believe the findings are consistent with previous theories of Earth's early atmosphere having a thick organic haze similar to that on Titan.
However their simulations suggests Earth's atmosphere repeatedly transitioned between two main atmospheric states, one haze free, the other thick in hydrocarbons.
Zerkle and colleagues attribute the transitions to changes in the rate of methane production by microbes.
They say the hydrocarbon haze didn't permanently retreat until the oxygenation of the atmosphere some 100 million years later.
Professor Malcolm Walter from the Australian Center for astro-biology at the University of New South Wales says the paper confirms a very large change in the chemistry of the Earth's surface about 2.65 billion years ago.
Read more at Discovery News
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