Earth once had hazy methane atmosphere like ice-moon Titan

Microbial flatulence dominated the pre-oxygen era

Billions of years ago, before Earth's atmosphere had oxygen, it periodically possessed a "haze" of organic chemicals including methane, boffins have discovered. During these periods the planet's air was more like that of Titan, ice moon of Saturn, than the stuff we breathe today.

"Models have previously suggested that the Earth's early atmosphere could have been warmed by a layer of organic haze," says Dr Aubrey Zerkle of Newcastle uni. "Our geochemical analyses of marine sediments from this time period provide the first evidence for such an atmosphere."

According to Zerkle and his colleagues, during the period 2.5 to 2.65 billion years ago, microbes were already producing oxygen in the oceans. However very little of this made it into the nitrogen atmosphere; instead there was a fluctuating haze of hydrocarbons, mainly methane (aka natural gas) but with some ethane and propane (patio gas) mixed in. This is similar to the present-day atmosphere on Titan, the giant ice-moon of Saturn, though it's so cold there that the hydrocarbons often fall as rain to form lakes. (Water behaves more like rock.)

Methane is still considered an important atmospheric gas by climate scientists today, as it has a greenhouse effect many times more powerful than carbon dioxide. Zerkle and his colleagues consider that their insights into the past atmosphere could be useful in refining our understanding of our planet's climate today.

"Besides the obvious importance for the evolution of the atmosphere, the role of aerosol formation is one of the most poorly understood components in the present day climate models," explains Professor Mark Thiemens of San Diego. "This provides a new look into this process that is quite new and valuable."

The new boffinry is published in the journal Nature Geoscience. ®

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