Earth’s atmosphere used to be half as thick as it is today

Miniature air bubbles trapped in 2.7 billion-year-old volcanic rock have revealed that the Earth’s atmosphere was once much thinner, and that the air pressure was half of its current levels, a team of American and Australian researchers reported this week in the journal Nature Geoscience.

Lead author Sanjoy Som, formerly a researcher with the University of Washington and now the director of the Blue Marble Space Institute of Science, and colleagues from the Denver Museum of Nature and Science and the University of Western Australia analyzed the relative sizes of gas bubbles trapped in ancient basalt rock formed in the Pilbara region of Western Australia.

They found evidence that the atmosphere would have been much lighter and thinner than it is today, which contradicts the long-held hypothesis that the early Earth had a thicker atmosphere in order to compensate for a sun than was 20-percent dimmer than today, and which will force scientists to reevaluate why the planet managed to remain largely ice-free during that time.

“All the signs are that it wasn’t that different, in terms of the climate system from today,” UW professor Dr. David Catling, one of the authors of the new study, told AFP. “There was rainfall and rivers, there might have been polar ice caps, but it was warm enough… for the whole world [not] to be covered in ice.”

Findings have implications for the search for life on other planets

Som, Catling and their colleagues analyzed air bubbles trapped in basalt throughout ancient lava flows along the coast of the Beasley River in Pilbara, and compared those trapped at the surface of the lava (which were limited in size only by the air pressure) to those at the base (which were limited by both atmospheric pressure and the weight of the lava).

This enabled them to calculate the air pressure at the time the lava flow took place, and based on the evidence they collected, the researchers concluded that the atmosphere was much thinner and weighed less than half of what it currently does. So what was keeping the Earth warm enough to prevent water from freezing and the surface of the planet from being coated in ice?

As it turns out, it was a combination of “greenhouse gases like carbon dioxide or methane” and lower levels of nitrogen than previously thought. High concentrations of CO2 and methane could have warmed the Earth, even with thinner air surrounding the planet, and the low pressure would have meant that nitrogen produced by microbes would have been “modulated” in a different way that limited how much reached the air, Dr. Catling explained to the AFP.

The results of the research demonstrate that “a planetary environment completely different than modern Earth can sustain life on its surface,” Som told Reuters. “Life doesn’t need conditions like modern Earth to survive and thrive,” he added. “This is important in our quest for habitable environments in extra-solar planets.”

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Image credit: Thinkstock

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