Instead, the team calculated the effects of much smaller impactors on Earth’s atmosphere. Given the diversity of noble gases like helium-3 deep inside the Earth today, the researchers concluded that it is unlikely that such a giant, core-melting impact occurred. However, if such a giant collision occurred, it should also melt everything within the planet, turning its interior into a homogenous slurry. A collision with an impactor as massive as Mars, the researchers found, would generate a shockwave through the Earth’s interior, setting off significant ground motion - similar to simultaneous giant earthquakes around the planet - whose force would ripple out into the atmosphere, a process that could potentially eject a significant fraction, if not all, of the planet’s atmosphere. The team performed numerical analyses, calculating the force generated by a given impacting mass at a certain velocity, and the resulting loss of atmospheric gases. The group examined how much atmosphere was retained and lost following impacts with giant, Mars-sized and larger bodies and with smaller impactors measuring 25 kilometers or less - space rocks equivalent to those whizzing around the asteroid belt today. Schlichting and her colleagues have published their results in the journal Icarus. “It gives us a new starting point for trying to understand what was the composition of the atmosphere, and what were the conditions for developing life.” “ sets a very different initial condition for what the early Earth’s atmosphere was most likely like,” Schlichting says. Hilke Schlichting, an assistant professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says understanding the drivers of Earth’s ancient atmosphere may help scientists to identify the early planetary conditions that encouraged life to form. But taken together, many small impacts would have the same effect, at a tiny fraction of the mass. Based on their calculations, it would take a giant impact - almost as massive as the Earth slamming into itself - to disperse most of the atmosphere. In fact, the researchers found that small planetesimals may be much more effective than giant impactors in driving atmospheric loss. Such impacts may have also blasted other planets, and even peeled away the atmospheres of Venus and Mars. Tens of thousands of such small impacts, the researchers calculate, could efficiently jettison Earth’s entire primordial atmosphere. Now researchers at MIT, Hebrew University, and Caltech have landed on a likely scenario: A relentless blitz of small space rocks, or planetesimals, may have bombarded Earth around the time the moon was formed, kicking up clouds of gas with enough force to permanently eject small portions of the atmosphere into space. ![]() ![]() However, it’s unclear what interplanetary forces could have driven such a dramatic loss. ![]() Today’s atmosphere likely bears little trace of its primordial self: Geochemical evidence suggests that Earth’s atmosphere may have been completely obliterated at least twice since its formation more than 4 billion years ago.
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