The dinosaurs were wiped out 65 million years ago by a meteor shower lasting thousands of years, a study has suggested.
Scientists had previously identified the a giant Chicxulub crater in the Gulf of Mexico as the site of a single meteor strike thought to have obliterated prehistoric life on Earth.
But evidence for a second impact in Ukraine, dating back thousands of years before the Chicxulub impact, has raised the possibility that the dinosaurs may have been blitzed with a shower of meteorites
The Boltysh Crater in Ukraine was first discovered in 2002. But scientists have now unearthed a second cavity within the crater which they believe was caused by the aftermath of the Chicxulub impact – suggesting that the two meteor strikes occurred years apart as part of a wider “shower”.
Scientists dated the two Boltysh impact zones by examining the pollen and spores of fossil plants in the layers of mud within.
Ferns are among the first plants to colonise a devastated landscape after a catastrophe, leaving layers of spores – dubbed “fern spikes” – which are considered good markers of past impact events.
The researchers found a second “fern spike” one meter above the first in the Boltysh crater – suggesting that two separate strikes occurred thousands of years apart.
Professor Simon Kelley of the Open University, who co-authored the study, said: "We interpret this second layer as the aftermath of the Chicxulub impact."
He continued: "It is quite possible that in the future we will find evidence for more impact events."
Professor Monica Grady, a meteorite expert at the Open University, said the shower could have been caused by "the collison of Near Earth Objects".
Nasa, the US space agency, recently launched a program called "Spaceguard" which aims to monitor such Near Earth Objects as an early warning system of possible future collisons.
The new findings are published in the journal Geology by a team lead by Professor David Jolley of Aberdeen University.