When it comes to explaining why the woolly mammoths died out, "death from above" could be down for the count. Nearly 13,000 years ago, North American megafauna like the mammoths and giant sloths—and even human groups like the people of the Clovis culture—disappeared as the climate entered a cold snap. As DISCOVER has noted before, there's been a controversial hypothesis bubbling up saying that a comet impact caused it all, but other scientists have been shooting holes in that idea of the last couple years. In a study in this week's Proceedings of the National Academy of Sciences, a team led by Tyrone Daulton pooh-poohs what may be the last major evidence that supports the impact idea. That evidence takes the shape of nano-diamonds in ancient sediment layers, a material said to form during impacts only.
These 12,900-year-old sediments were claimed to hold exotic materials: tiny spheres, ultra-small specks of diamond -- called nanodiamond -- and amounts of the rare element iridium that are too high to have occurred naturally on Earth. [BBC News]
Impact proponents published their own studies last year in Science
that set forth the nano-diamond argument. But when Daulton and company searched the sediment and examined it under transmission electron microscopes, they couldn't find any.
"I'm convinced there's no [hexagonal] diamond present," says Daulton. Instead, the group unearthed aggregates of sheetlike forms of carbon. "If you don't look too closely at it, you could convince yourself it is [hexagonal diamond]," says Daulton. "Theirs was a gross misidentification." [ScienceNOW]
Unsurprisingly, the impact-backing scientists didn't care for the assertion that they talked themselves into seeing diamonds.
The lead author of two earlier comet-impact papers, Douglas Kennett, an archaeologist at the University of Oregon in Eugene, calls the study "fundamentally flawed science". "The claim we misidentified diamonds is false, misleading and incorrect," he adds, although he declined to specify his objections. [Nature]
However, he did promise to write PNAS with his objections and to point out errors he says are in Daulton's work. Related Content: 80beats: Nano-Diamond Discovery Suggests a Comet Impact Killed the Mammoths
Image: Wikimedia Commons / Tracy O