Greenhouse gases may have loaded early atmosphere

Earth

Ancient Earth may have been warmed by the presence of greenhouse gases, which made life possible on our planet, a new study, including Indian origin scientist, has suggested.

In ancient Earth history, the sun burned as much as 30 percent dimmer than it does now.

Theoretically that should have encased the planet in ice, but there is geologic evidence for rivers and ocean sediments between 2 billion and 4 billion years ago.

Scientists have speculated that temperatures warm enough to maintain liquid water were the result of a much thicker atmosphere, high concentrations of greenhouse gases or a combination of the two.

Now University of Washington researchers, using evidence from fossilized raindrop impressions from 2.7 billion years ago to deduce atmospheric pressure at the time, have demonstrated that an abundance of greenhouse gases most likely caused the warm temperatures.

 "Because the sun was so much fainter back then, if the atmosphere was the same as it is today the Earth should have been frozen," said lead author Sanjoy Som, a postdoctoral researcher at NASA's Ames Research Center, Mountain View, Calif., who conducted the research as part of his UW doctoral work in Earth and space sciences.

He and his coauthors – David Catling and Roger Buick of UW Earth and space sciences; Jelte Harnmeijer, a UW graduate now at the Edinburgh Centre for Low Carbon Innovation in Scotland; and Peter Polivka, a UW graduate student in civil engineering – set out to determine how the ancient atmosphere differed from that of today.

The new work allowed the scientists to determine limits of ancient air pressure by comparing raindrop impressions from today with the fossilized impressions from a time when there were no plants or animals on Earth but the planet was teeming with microbes.

The sizes of raindrop impressions depend on raindrop velocity, the atmospheric pressure and the composition of material into which the raindrops fall.

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