Did a comet impact really kill off megafauna such as the mammoth, mastodan and sabre-tooth tiger?
Credit: Wikimedia
PORTLAND, OREGON: Debate on the existence of a Younger Dryas comet impact, 12,900 years ago, and whether it is linked to mass extinctions of large mammals and early humans in North America reopened this week.
The Younger Dryas was a 1,300-year-long cold snap that affected climate in much of the Northern Hemisphere. In 2007, a team led by Richard Firestone of Lawrence Berkeley National Laboratory, in the U.S., argued that it was caused by the impact of a comet.
This then wiped out such Pleistocene megafauna as the sabre-toothed cat, the mastodon and the mammoth, along with the Clovis people, one of the earliest American cultures.
Impact markers
In support, Firestone's team cited a number of impact markers, dated about 12,900 years ago, as evidence of the exploding comet and its impact on cooling patterns resulting in mass extinction. These included tiny spheres, called spherules, made of metals and carbon and minute, shattered diamonds caused by the detonation. They also found unusual concentrations of helium 3 and iridium, common in impact sites, but rare in the Earth's crust.
"The impact layer at some sites is directly covered by a black algal mat that is in direct contact with mammoth bones and Clovis artefacts," Firestone told Cosmos Online. "The mat was literally peeled off of the bones with dental picks and adhering to the bones were impact markers."
But the study has proved to be controversial. "When I saw the study, I found it compelling," said Todd Surovell, an anthropologist at the University of Wyoming in Laramie. "But I wanted to see this patterning for myself."
Miscounted spherules
What Surovell and other scientists found wasn't what they'd initially expected. "Using the same methods on similar samples, we should have found the same results - we did not," he said. The results were revealed this week at the Geological Society of America's annual meeting in Portland, USA.
Part of the problem may have been methodology. Spherules, which are smooth glassy metallic grains common at impact sites, may have been miscounted, depending on how they were categorised. "When is a sphere a sphere?" said Surovell. "Definitional issues may have gotten in the way when it wasn't clear what counted as evidence."
Surovell's own study counted only those grains that were well rounded, highly spherical, and exhibited a smooth glassy or metallic surface. "Magnetic grains that are irregularly shaped and often sub-rounded are more abundant than micro-spherules," said Surovell, the implication being that counting them might have skewed the earlier study's results. "This [later] study employed a conservative definition."
Clovis Comet \ Younger Dryas Boundary
Holly Hight's article on the Younger Dryas Clovis Comet was poorly balanced and uninformed. Just take a look at all the information available on the web beyond Todd Surovell's presentation at GSA. There are NINE oral presentations presenting evidence pro and con to come at AGU, they might have deserver a mention.
Also twenty posters of which Surovell is one contribution.
Reading Hight's article you would think Surovell was the only researcher addressing the subject. Richard Firestone, though the original researcher, is not in the lead -- as is clear from the team's last dozen publications.
George Howard
This is not a journal
George: you miss the point of a science journalism: it is not about attributing researchers, it is about reporting for the public on new developments in science.
Holly might have attended all the sessions at GSA and found Surovell's presentation the best and clearest, or the one that translated best into an article. She makes no claim that he's the only researcher in the field.
Science journalists may love science, but their first loyalty is to their audience, making science interesting and engaging and bringing hem something they didn't know. It is not about making establishing a priori or making sure all of the researchers who have anything to do with a field are appropriately identified or have their egos stroked.
A Really Big Story
First off, several of the First Peoples preserved accounts of this comet impact. As there is no reason for them to have made these accounts up, an impact occured.
Second, denial is a natural human response to threats which people think that they can not deal with. One notes that Keller's claims that the Chicxulub impact did not kill off the dinosaurs are reported annually, but that the refutations seldom get any press.
Third, controversy sells, and as many professionals have their careers invested in other explanations for this extinction, this is going to be a real fight, good for lots of copy.
Fourth, NASA research money for Earth impacts is $0.
Fifth, former NASA Adminstrator Michael Griffin ignored the direct instructions from the Congress (Senate and House, Republican and Democratic members) to find these things before they hit.
And that is going to be a Really Big Story, whenever it finally gets reported.
E.P. Grondine
Man and Impact in the Americas