The Northern Lights have seen strange sights, but nothing weirder than what befell a gaggle of woolly mammoths lumbering across the Siberian tundra some 30,000 years ago-- the sky lit up with a bang as they were struck by a hail of micrometeorites the size of shotgun pellets.
How many were struck dead by larger fragments, or blind by lesser ones is problematic, but nickel iron pellets have been found, only on the skyward side , of seven Yakutian fossil mammoth tusks and a horned bison skull found in Alaska according to a paper researchers Allen West and Richard Firestone presented on 11 December at the American Geophysical Union meeting in San Francisco.
"We think that the micrometeorites came from an air-burst of a meteor 30,000 to 34,000 years ago," Firestone, a chemist at the Lawrence Berkeley National Laboratory told Nature "We think a wave of meteoric material sprayed the region."
Some of the tusks are peppered with hundreds of the 2 to 5 millmeter nickel-iron fragments, which burned grooves into the bone. Strangely, the damage to the tusk was first noted not by the fearless mammoth hunters of Yakutia, but an observant rockhound at a fossil sale in a motel in Arizona.
According to Nature :
Allen West,[ who lives in Arizona] was looking for evidence of a meteorite that he and his colleagues hypothesize caused the megafaunal extinction and decline of the Clovis people in North America some 13,000 years ago. Recalling previous visits to the annual Tucson Gem and Mineral Show, West says, "A bulb went on in my head; I remembered seeing a room full of mammoth tusks there." So he went to a motel that shows the fossils, and sifted through the tusks.
"I spent two or three hours looking at dirty old tusks, when suddenly there was a burnt hole," he says. He tested it with a small magnet, as he knew many meteorites were mostly iron. "Bang; it stuck right to the hole," he says.
West bought the 60-centimetre tusk for about US$200, and later headed to the warehouse of the company that he bought it from: Canada Fossils.
After three days of searching through the company's collection of some 15,000 tusks, West started to find more evidence of micrometeorites in a batch from the Yukutia Peninsula in eastern Siberia. His magnet again repeatedly hit the mark on tell-tale burn holes.
West bought these tusks too and took them to Firestone and his colleagues for geochemical analysis and radiocarbon dating