A massive asteroid collision 470 million years ago could hold clues on how to stop global warming.
The crash in the asteroid belt between Mars and Jupiter triggered an ice age on Earth and paved the way for the evolution of new species.
Scientists already knew about the ice age but they did not know the reason for it.
They examined traces of space dust in 466-million-year-old rocks from a fossil site in Sweden, looking for a type of helium isotope often found in asteroids.
They found that a large amount of debris thrown into the atmosphere by the collision had partially blocked the sunlight from Earth.
Study author Philipp Heck, a curator at the Field Museum in Chicago and associate professor at the University of Chicago, said: “Normally, Earth gains about 40,000 tonnes of extraterrestrial material every year.
“Imagine multiplying that by a factor of a thousand or 10,000.”
The dust floated towards Earth over two million years, gradually cooling the planet and allowing new species to adapt.
It also divided the planet into zones – colder temperatures at the outer extremes and warmer conditions at the equator.
Scientists say that the finding, documented in the journal Science Advances, could help them explore different ways the planet could be cooled artificially.
Birger Schmitz, professor of geology at Lund University and the leader of the study, said the result was “completely unexpected”.
“We have during the last 25 years leaned against very different hypotheses in terms of what happened,” he said.
“It wasn’t until we got the last helium measurements that everything fell into place.”
Finding a way to cool the Earth could help prevent a major climate crisis.
Previously, scientists have used computer simulations to show asteroids could orbit Earth in a way that allows them to create fine dust which blocks the sunlight.
Mr Schmitz said: “Our results show for the first time that such dust at times has cooled Earth dramatically.
“Our studies can give a more detailed, empirical based understanding of how this works, and this in turn can be used to evaluate if model simulations are realistic.”
Mr Heck was more cautious, saying any ideas needed to be looked at “very critically and very carefully, because if something goes wrong, things could become worse than before”.