An ancient meteor impact in North America sent up waves of rock fragments that peppered prehistoric mammals with "space shrapnel" about 34,000 years ago, scientists say.
Many of the animals, particularly in the region near present-day Alaska, didn't survive.
That's the story being pieced together by a research team led by Richard Firestone of the Lawrence Berkeley National Laboratory in Berkeley, California.
The team had done previous work on a suspected impact that occurred 13,000 years ago. But while looking for evidence of that more recent blast in mammoth tusks, the scientists found traces of the much older event.
"The surprise was the tusks were dating back to 30,000 to 34,000 years ago," Firestone said.
"Nobody had thought of it before. It was serendipitous."
The work was presented this week at the fall meeting of the American Geophysical Union in San Francisco, California.