From the Daily Mail:
They believe a huge meteor smashing through the Earth's atmosphere broke up into ten million tonnes of fiery fragments, scattering over four continents.
These fragments are thought to have released toxic gas which poisoned the air and blacked out the sun, causing temperatures to plummet, plants to die and landscapes to alter forever.
Research published in the Proceedings of the National Academy of Sciences suggests that this caused the extinction, countering previous theories that the spread of human settlements and aggressive hunting was to blame.
After the impact, some animal species, like humans, adapted by either moving away, downsizing to adapt to the resources around them, or simply changed their way of life to cope.
But other species, including the woolly mammoth which roamed throughout Europe, parts of Asia and North America in vast numbers, did not adapt and were wiped out in a generation.