Mysterious iron-filled mammoth tusks intrigue scientists
Mysterious iron-filled mammoth tusks intrigue scientistsNed RozellPublished Sunday, March 9, 2008Photo Courtesy of Richard FirestoneEmbedded iron particles surrounded by carbonized rings in the outer layer of a mammoth tusk from Alaska. The inset photo shows how an object ripped through the tusk.
A giant meteor may have exploded over Alaska thousands of years ago, shooting out metal fragments like buckshot, some of which embedded in the tusks of woolly mammoths and the horns of bison. Simultaneously, a large chunk of the meteor hit Alaska south of Allakaket, sending up a dust cloud that blacked out the sun over the entire state and surrounding areas, killing most of the life in the area.
Such is the scenario envisioned by Rick Firestone, a staff scientist at the Lawrence Berkeley National Laboratory in California. Firestone and his colleagues have found mammoth tusks and a bison skull with nickel-rich iron particles in them on one side, suggesting the metal fragments all came from the same direction.
Firestones theory emerged when his colleague, Alan West of Dewey, Ariz., saw at a Phoenix gem and mineral show a mammoth tusk peppered with tiny bits of metal. Intrigued, West and Firestone looked at tusks owned by the same dealer in Calgary. By passing a magnet over mammoth tusks in Calgary, Firestone and West found seven mammoth tusks collected somewhere near the Yukon River and a bison skull from Siberia that had tiny iron fragments burned into them. The fragments also contained nickel.
One in 1,000 tusks had this material in it, Firestone said.
Firestone also thinks he may have found the divot left by the ancient meteorite, an impact crater that is now occupied by a round body of water named Sithylemenkat Lake in the upper Kanuti River drainage.
The creeks coming out of the lake are very rich in nickel, Firestone said, referring to a metal associated with meteorites. And the shape is consistent with a crater from a meteorite that may have been a half a kilometer in diameter a pretty large thing.
A meteorite that big would have torched anything within a 100-mile radius and could have buried the mammoths farther away from the crater, preserving the tusks struck by metal fragments. Firestone said the dust kicked up by the meteor would have eliminated any mammoths that survived the meteors hit...
Dale Guthrie, one of Alaskas few experts on mammoths, said he found Firestones theory interesting, but Alaska scientists who know about impact craters think he is probably off on his guess that Sithylemenkat Lake is the place where a giant meteorite struck about 35,000 years ago (the approximate age of the mammoth tusks). Scientists have confirmed only one impact crater in Alaska called Avak, near Barrow and have discovered only about 140 impact craters on the entire planet...
Buck Sharpton, an expert on impact craters and the vice chancellor for research at the University of Alaska Fairbanks, said the lake would have to be much older than 35,000 years because it has no rim associated with more recent impact craters and doesnt look to him like an impact crater. He thinks the iron bits in the tusks could be cavities filled by being immersed for millennia in porous sedimentary fill through which iron-rich water percolated.