Ancient Bubbles Reveal: Earth’s Early Atmosphere Was Thin

MessageToEagle.com – Researchers from the University of Washington have used bubbles trapped in 2.7 billion-year-old rocks to show that air at that time exerted at most half the pressure of today’s atmosphere.

The results, published online May 9 in Nature Geoscience, reverse the commonly accepted idea that the early Earth had a thicker atmosphere to compensate for weaker sunlight.

“For the longest time, people have been thinking the atmospheric pressure might have been higher back then, because the sun was fainter,” said lead author Sanjoy Som, who did the work as part of his UW doctorate in Earth and space sciences.

“Our result is the opposite of what we were expecting.”

The idea of using bubbles trapped in cooling lava as a “paleobarometer” to determine the weight of air in our planet’s youth occurred decades ago to co-author Roger Buick, a UW professor of Earth and space sciences.

Others had used the technique to measure the elevation of lavas a few million years old. To flip the idea and measure air pressure farther back in time, researchers needed a site where truly ancient lava had undisputedly formed at sea level.

The bubbles indicate that the atmospheric pressure at that time was less than half of today’s.

Earth 2.7 billion years ago – home only to single-celled microbes – had atmosphere that contained no oxygen, sunlight was about one-fifth weaker.

This finding points to conditions being even more otherworldly than previously thought. A lighter atmosphere could affect wind strength and other climate patterns, and would even alter the boiling point of liquids.

The new study is an advance on the UW team’s previous work on “fossilized raindrops” that first cast doubt on the idea of a far thicker ancient atmosphere. The result also reinforces Buick’s 2015 finding that microbes were pulling nitrogen out of Earth’s atmosphere some 3 billion years ago.

“The levels of nitrogen gas have varied through Earth’s history, at least in Earth’s early history, in ways that people just haven’t even thought of before,” said co-author David Catling, a UW professor of Earth and space sciences. “People will need to rewrite the textbooks.”

The study is published in the Journal of Nature Geoscience.

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