Mammoths Doomed by Hunting, Climate: Study

Aug. 3, 2009 -- It's the question at the heart of an age-old murder mystery: Who or what killed off the mammoths?

A new study has found that overhunting by our ancestors, coupled with a sharp cooling event around 12,900 years ago, may have led to the mammoth's demise.

Four years ago, a group of scientists proposed that a comet or asteroid may have killed off mammoths, smacking into a thick ice sheet that was receding across Canada or breaking up in a rain of fire that scorched North America.

Hints of an impact have been documented in the geological record, but no smoking gun -- in the form of a crater -- has emerged.

Evidence from a few placid lakes in Indiana and Ohio suggests that there may never have been such a collision. Sediments from Silver Lake in Ohio, and Appleman and Spicer Lakes in Indiana show no signs of silicon spherules -- which would be likely if a large impact occurred anywhere in the region -- and no charcoal, ruling out a continent-wide firestorm.

Appleman Lake also shows that spores of the fungus Sporomiella decline sharply around 14,500 years ago. The fungus is only known to grow on dung from large mammals, including mammoths. Its absence points to the extinction of mammoths and other large beasts from the area almost two millennia before the cataclysm is supposed to have occurred.

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Additionally, several species of megafauna and lesser animals were in decline. At the same time, humans had just developed sophisticated Clovis spear points, which undoubtedly increased their ability to kill large prey.

Taking this evidence together, researchers came to the conclusion that overhunting by humans, along with a sharp decline in temperatures in the Northern Hemisphere, led to the extinction of the mammoths.

"The impact (of a comet or asteroid) is an attractive hypothesis, because it provides an explanation for the whole range of things we see going on at this time," Jacquelyn Gill of the University of Wisconsin-Madison said. Gill led a team of researchers on the study, which is being presented this week at the annual meeting Ecological Society of America.

"I wouldn't be surprised if the real story is much more complicated than that," she said.

Richard Firestone of Lawrence Berkeley National Laboratory disagrees. Firestone first suggested the impact theory and acknowledged that humans were actively hunting mammoth. However, he said there were too few people around to account for the extinction.

"The human population was just not that large. Humans were opportunistic hunters, and they probably killed sick or weak mammoths," he said. "But the number of animals on the landscape compared to humans was too large, and hunting a full-grown mammoth in the open would've been very dangerous. The idea that people could've kills all mammoths doesn't make sense."

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