Diamonds Show Comet Struck North America
Diamonds show comet struck North America, scientists say
The impact caused an ice age that killed some mammal species and many humans 12,900 years ago, researchers report. They say the discovery of tiny heat-formed diamonds is proof of the catastrophe.
By Thomas H. Maugh II
January 02, 2009
A thin layer of miniature gemstones called nanodiamonds in North American soil provides the strongest evidence yet that a comet struck the continent nearly 13,000 years ago, triggering a mini-ice age that wiped out many species of mammals and interrupted the culture of early humans for hundreds of years.
Researchers had earlier discovered the thin layer of black soil containing iridium and other debris suggestive of a massive comet or meteor impact, but critics had suggested a variety of less dire explanations.
The discovery of the nanodiamonds, however, reported today in the journal Science, provides the most powerful support for the comet theory because the gems can only be created under the extreme temperatures and pressures of a massive explosion, such as a comet striking the Earth’s surface.
“There’s no other way we can interpret the presence of these diamonds other than an extraterrestrial impact,” said paleooceanographer James P. Kennett of UC Santa Barbara, one of the authors of the paper.
Such an impact would be the most likely source of nanodiamonds, critics agreed, but many argued that the one-page paper in Science does not provide enough evidence to support the authors’ claim.
“Nanodiamonds could be a good indicator of an impact event . . . but after reading the paper, I wasn’t convinced they found diamonds,” said physicist Tyrone Daulton of Washington University in St. Louis. “Maybe they found diamonds, and maybe they didn’t.”
Added spectroscopist Peter Buseck of Arizona State University, “I wouldn’t question that they saw nanodiamonds,” but for such a potentially important discovery, “I would like to have it well-supported.”
Archaeologist Douglas J. Kennett of the University of Oregon, lead author of the report and James Kennett’s son, conceded that the restrictive format of the rapid publication limited the amount of data the team could incorporate.
But he said the presence of nanodiamonds had now been confirmed in three separate laboratories: “There are going to be a lot of follow-up papers that will clearly demonstrate that these are diamonds.”
The new findings may tie together a variety of hitherto mysterious events in North America that all occurred around the same time.
Beginning about 12,900 years ago, North America — and perhaps the entire world — entered a 1,300-year-long period of profound cooling known as the Younger Dryas, and often colloquially called the “Big Freeze.”
About that same time, at least 35 species of large mammals, such as the woolly mammoth, camels and mastodons, disappeared forever. The period also saw an end to the Paleo-Indian Clovis culture characteristic of the first inhabitants of the continent.