SEATTLE, March 28 (UPI) -- Fossil raindrop impressions suggest greenhouse gases warmed an early Earth that should have been icy under a dimmer sun than we have now, U.S. researchers say.
In Earth's ancient past, the sun burned as much as 30 percent dimmer than it does now, which should have had our planet encased in ice, but there is geologic evidence for rivers and ocean sediments between 2 billion and 4 billion years ago, the University of Washington reported Wednesday.
"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," Sanjoy Som, a researcher at NASA's Ames Research Center in Mountain View, Calif., said.
Som conducted the research as part of his UW doctoral work.
Using evidence from fossilized raindrop impressions from 2.7 billion years ago to deduce atmospheric pressure then, the researches demonstrated that an abundance of greenhouse gases -- created by microbes teeming on the planet --most likely caused the warm temperatures.
"Setting limits on atmospheric pressure is the first step towards understanding what the atmospheric composition was then," Som said.
Som said the finding could prove important in the search for life on planets orbiting other stars because the Earth of 2.7 billion years ago was very different from what we know today, and yet it supported abundant life in the form of microbes.
"Today's Earth and the ancient Earth are like two different planets," he said.