Earth's Ancient Atmosphere Weighs Less Than Half of Today's Atmosphere, Study Shows

For the last decades scientists believed that the Earth's ancient atmosphere has a stronger greenhouse and thicker atmosphere than we have today to compensate for the weaker sunlight during that time, but a new study reveals that this assumptions are wrong.

According to the study published in the journal Nature Geoscience, the ancient atmosphere of Earth 2.7 billion years ago was between a quarter to half as thick as it is today. This discovery forces scientist to re-examine everything they know about Earth's early atmosphere.

"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, said in a statement. "Our result is the opposite of what we were expecting."

For the study, researchers analyzed air bubbles trapped in 2.7-billion-year-old flood basalts from the Pilbara region of Western Australia. Using high-precision X-ray scans, researchers measured the decrease in the size of bubbles between the top and the bottom layer of the lava.

According to a press release, "by measuring the size of the bubbles at the top-which were pushing against the weight of the atmosphere-and comparing them with the smaller bubbles at the bottom-which were pushing against both the atmosphere and the weight of the rock itself-the team came up with a proxy for ancient air pressure."

After observing the bubbles, the researchers were surprised to discover the ancient atmosphere must have been much lower than previously assumed, basing from the size of bubbles exposed at the surface of the lava.

Researchers theorized that the low atmospheric pressure during 2.7 billion years ago was caused by the development of the nitrogen-fixation ability of some single-cell organisms. During nitrogen-fixation, bacteria mine nitrogen from the air and turn it into ammonia. The sudden rise of nitrogen fixating bacteria made the nitrogen levels in the atmosphere to drop causing the air pressure to considerably decease temporarily.

With their findings, there is possibility that many of the information we know today about early life may be incorrect.