Tiny bubbles that were trapped inside 2.7 billion-year-old rocks have led scientists to conclude that Earth’s atmosphere was less than half as dense as it is today – which runs counter to conventional wisdom.
Scientists had assumed that our planet’s atmosphere was thicker billions of years ago, in order to retain heat and keep the planet warm enough for life during an era when the sun shone less brightly than it does today.
“Our result is the opposite of what we were expecting,” Sanjoy Som, an astrobiologist at NASA’s Ames Research Center in California, said in a news release from the University of Washington.
Som is the principal author of a study reporting the findings, published today by Nature Geoscience. He conducted the research during his doctoral studies at the UW, and retains a Seattle connection as the CEO of a nonprofit space science outreach group called Blue Marble Space.
The findings are based on an analysis of atmospheric bubbles that were left behind in basaltic lava flows from Western Australia’s Pilbara Craton. Based on the size of the now-solidified bubbles, Som and his colleagues determined that the atmospheric pressure must have been surprisingly low, ranging between a quarter and a half of today’s pressure.
To breathe air that thin today, you’d have to climb to the top of Mount Everest.
During the time frame that’s the focus of the research, known as the Neoarchean Era, Earth was home only to single-celled microbes. Sunlight was about a fifth weaker than it is today, and the atmosphere was just in the process of building up significant amounts of oxygen.
If the atmosphere was as thin as the bubbles in the rocks indicate, there were probably higher proportions of heat-trapping greenhouse gases such as methane and carbon dioxide. The researchers say that would provide the best explanation for how life and liquid water could endure.
The results also suggest there were wide variations in atmospheric pressure throughout Earth’s history.
“We’re still coming to grips with the magnitude of this,” said Roger Buick, a professor of Earth and space sciences at the UW. “It’s going to take us a while to digest all the possible consequences.”
The study may have consequences for astrobiologists as well. If life could arise on Earth when it had a surprisingly thin atmosphere, that could lead scientists to recalibrate their assumptions about the potential for habitable conditions on ancient Mars, or on planets orbiting distant stars.
In addition to Som and Buick, the authors of the Nature Geoscience study, “Earth’s Air Pressure 2.7 Billion Years Ago Constrained to Less Than Half of Modern Levels,” include James Hagadorn, Tim Blake, John Perreault, Jelte Harnmeijer and David Catling. The research was funded by NASA.
