When Earth was young, its surface was probably covered in a magma ocean, and the gases rising from that seething sea may have provided it with an atmosphere nearly identical to the toxic one present on Venus today.
Earth’s early magma ocean was probably created by a collision with a Mars-sized object that melted much of the young planet and created the moon. As the magma ocean cooled, some compounds would have evaporated out of the molten mix and formed an atmosphere.
To figure out what this atmosphere would have been like, Paolo Sossi at ETH Zürich in Switzerland and his colleagues used a technique called aerodynamic levitation to float a small pellet of rock atop a jet of gas while heating it to about 1900°C with a laser to melt it.
“This little melted marble floating at almost 2000 degrees is sort of a miniature Earth in its molten state,” says Sossi. The gas flowing around the marble behaves as if it were a miniature atmosphere.
The researchers then repeated the experiment, altering the composition of the jet of gas by adding and removing different compounds to try to find the likely make-up of the atmosphere of the young Earth. The oxygen levels in the melted sample changed depending on the composition of the gas. They compared these molten marbles to samples of rock from Earth’s mantle to determine which atmosphere produced the best match with the geological record we have.
They found that this was a dense atmosphere full of carbon dioxide and with relatively little nitrogen, similar to the atmosphere on Venus today. Mars’s atmosphere has nearly the same composition, although it is much thinner.
The fact that Earth is larger than Mars – meaning it has enough gravity to hold onto its atmosphere – and cooler than Venus allowed liquid water to remain on its surface, extracting carbon dioxide from the atmosphere and preventing the planet from going through the runaway greenhouse effect that Venus experienced to become a sweltering hellscape.
Journal reference: Science Advances, DOI: 10.1126/sciadv.abd1387
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