A relentless blitz of small space rocks 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, an international team of researchers has discovered that.
Tens of thousands of such small impacts, the researchers calculated, could have efficiently jettisoned Earth's entire primitive atmosphere.
Such impacts may have also blasted other planets and even peeled away the atmospheres of Venus and Mars.
"The finding sets a very different initial condition for what the early Earth's atmosphere was most likely like. 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," said Hilke Schlichting, assistant professor of the department of earth at the Massachusetts Institute of Technology (MIT) in the US.
"Small space rocks may be much more effective than giant impactors in driving atmospheric loss," he added.
The group from MIT and the Hebrew University of Jerusalem examined how much atmosphere was retained and lost following impacts with space rocks measuring 25 km or less.
Such space rocks, upon impact, would generate an explosion of sorts, releasing a plume of debris and gas.
"The largest of these impactors would be forceful enough to eject all gas from the atmosphere immediately above the impact's tangent plane - the line perpendicular to the impactor's trajectory," Schlichting said.
To completely eject all of Earth's atmosphere, the planet would need to have been bombarded by tens of thousands of such small impacts - a scenario that likely did occur 4.5 billion years ago during a time when the moon was formed.
This period was one of galactic chaos as hundreds of thousands of space rocks whirled around the solar system, frequently colliding to form the planets, the moon and other bodies.
"For sure, we did have all these smaller impactors back then. One small impact cannot get rid of most of the atmosphere but collectively, they are much more efficient than giant impacts, and could easily eject all the Earth's atmosphere," Schlichting added.
According to Jay Melosh, professor at Purdue University, Schlichting's conclusion is a surprising one, as most scientists have assumed the Earth's atmosphere was obliterated by a single, giant impact.
The findings were detailed in the journal Icarus.
