An ancient asteroid collision may have filled the atmosphere with enough dust to trigger an ice age, scientists claim.
Sunlight-blocking dust remained in the sky for around two million years, effectively causing Earth to "freeze."
Scientists have long been puzzled by the cause of an ice age that took place 466 million years ago.
Now they think they've cracked it: a huge asteroid collision in outer space is to blame.
Dust is constantly floating down to Earth from space, made from broken parts of asteroids and comets.
But when 93-mile-wide asteroid broke apart between Mars and Jupiter, it created "way more dust than usual."
And this dust fell to Earth and impeded sunlight for as long as two million years.
"Normally, Earth gains about 40,000 tons of extraterrestrial material every year," said Philipp Heck, of the University of Chicago, and one of the Science Advances paper's authors.
"Imagine multiplying that by a factor of a thousand or ten thousand.
"Our hypothesis is that the large amounts of extraterrestrial dust over a timeframe of at least two million years played an important role in changing the climate on Earth, contributing to cooling."
The paper revealed that the alien dust cooled Earth dramatically.
First, researchers located extraterrestrial matter from the ground – in areas where the rocks were once on the seafloor.
They then used acid to eat away the stone and leave "the space stuff".
This research confirmed that the dust contained material originating from asteroids in space.
And through dating mechanisms, it's possible to verify that the dust fell around the same time as an ice age began.
"The timing appears to be perfect," said Birger Schmitz of Sweden's Lund University.
"The extra dust in the atmosphere helps explain the ice age--by filtering out sunlight, the dust would have caused global cooling."
The dust floated down to Earth over two million years, gradually cooling the planet.
Not all sunlight will have been blocked – but enough to change Earth's climate.
This allowed life to adapt "and even benefit" from the changes, sparking "an explosion of new species".
According to Heck, a faster-paced climate change could be much more catastrophic.
"In the global cooling we studied, we're talking about timescales of millions of years," he explained.
"It's very different from the climate change caused by the meteorite 65 million years ago that killed the dinosaurs, and it's different from the global warming today.
"This global cooling was a gentle nudge. There was less stress."
This story originally appeared in The Sun.