Researchers studying a dark layer of dirt at 10 sites around North America say they have found evidence that an asteroid or a comet may have killed the woolly mammoths, giant sloths, camels and other huge creatures that once roamed the continent.
The international team of researchers looked under what is known as "black mat" sediment, which dates back to 12,900 years ago. It coincides with a period of abrupt global cooling known as the "Big Freeze," or the Younger Dryas.
They found high concentrations of iridium, nanodiamonds, soot, charcoal and other chemicals and compounds that suggested a celestial body had crashed into the Earth and started raging, massive wildfires.
"We don't have a smoking gun for our theory, but we sure have a lot of shell casings," said Peter Schultz, a planetary geologist at Brown University in Rhode Island.
"Taken together, the markers found in the samples offer intriguing evidence that North America had a major impact event about 12,900 years ago."
There is compelling evidence that an asteroid or comet that landed in Mexico 65 million years ago led to the extinction of the dinosaurs. Researchers have also argued that a giant asteroid caused a mass extinction known as "the Great Dying" 251 million years ago. More than 90 per cent of marine species and most plants and animals disappeared.
More evidence is needed to make the case that an asteroid or comet took out the woolly mammoths, said Dr. Schultz. But he said it is sobering to consider that such a catastrophic event occurred in the relatively recent past.