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Early Planet Earth Had Thinner Atmosphere Than Today: Study

Reversing the age-old belief, scientists found that the young Earth atmospheric pressure 2.7 billion years ago was less than half of today’s.

In fact, it earth had a thicker atmosphere than today’s, said Indian-origin scientist Sanjoy Som from the University of Washington.

In a paper published in Nature Geoscience, Som and his team used bubbles trapped in 2.7 billion-year-old rocks in Australia to show that air at that time exerted at most half the pressure of today’s atmosphere.

Earlier, scientist believed that Earth had a thicker atmosphere to compensate for weaker sunlight. The new finding will trigger series of changes in views on implications of gases in ancient atmosphere and how biology and climate worked on the early planet.

“Our result is the opposite of what we were expecting,” said Som, pointing out the fact that for long people believed the atmospheric pressure might have been higher back then as the sun was fainter.

Researchers, chose a site where truly ancient lava had undisputedly formed at sea level and they found it in Western Australia, where the Beasley River has exposed 2.7 billion-year-old basalt lava.

The team drilled into the overlying lava flows to examine the size of the bubbles, a technique developed by Roger Buick, a University of Washington professor of Earth and space sciences.

A stream of molten rock quickly cools from top and bottom, and bubbles trapped at the bottom are smaller than those at the top. The size difference shows that the air pressure was pushing down on the lava as it cooled, 2.7 billion years ago.

The initial measurements in the field suggested a surprisingly lightweight atmosphere and more rigorous x-ray scans from several lava flows confirmed the result. These bubbles indicate that the atmospheric pressure at that time was less than half of today’s.

Earth 2.7 billion years ago was home only to single-celled microbes, sunlight was about one-fifth weaker, and the atmosphere contained no oxygen. The result also reinforces Buick’s 2015 finding that microbes were pulling nitrogen out of Earth’s atmosphere some 3 billion years ago.

“We’re still coming to grips with the magnitude of this,” Buick said. “It’s going to take us a while to digest all the possible consequences.”

Other geological evidence clearly shows liquid water on Earth at that time, so the early atmosphere must have contained more heat-trapping greenhouse gases, like methane and carbon dioxide, and less nitrogen.


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