Access
This article is part of Nature's premium content.
Published online 12 October 2009 | Nature | doi:10.1038/news.2009.997
News
North America comet theory questioned
No evidence of an extraterrestrial impact 13,000 years ago, studies say.
An independent study has cast more doubt on a controversial theory that a comet exploded over icy North America nearly 13,000 years ago, wiping out the Clovis people and many of the continent's large animals.
Archaeologists have examined sediments at seven Clovis-age sites across the United States, and did not find enough magnetic cosmic debris to confirm that an extraterrestrial impact happened at that time, says the report in the Proceedings of the National Academy of Sciences (PNAS)1.
To read this story in full you will need to login or make a payment (see right).
Comments
Reader comments are usually moderated after posting. If you find something offensive or inappropriate, you can speed this process by clicking 'Report this comment' (or, if that doesn't work for you, email webadmin@nature.com). For more controversial topics, we reserve the right to moderate before comments are published.
Jacquelyn Gill states in her thesis: "However, the peak in charcoal at 850 cm (which occurs after the initial [megafaunal]decline) may indicate an impact caused fire though more dates are needed to support this."
Her colleague, Katie Lininger also supports the impact hypothesis in her senior thesis: "A fire peak occurs contemporaneously with the onset of the Younger Dryas climatic event at 12,900 cal yr BP, supporting the hypothesis of an extraterrestrial impact at that time."
My paleofire research on four lakes near Flint Michigan (M.S. Geology, August 2009, University of Cincinnati)
shows fire evidence at the beginning of the Younger Dryas, as well as fire events during the Allerod.
I can't conclude the 12,900 BP fire was caused by an impact, because I am looking strictly at charcoal evidence of fire in lake sediments.
Joanne Ballard
It's always a relief when you can conclude that every study but yours is "flawed" isn't it. Well, yours and the ones that agree with the hypothesis you staked your name on. So much for following the evidence.
Here is a link to the Lininger thesis providing evidence in lake sediments for the impact hypothesis:
http://snipurl.com/si1gc
I have responded to the article written by Dr. Surovelle and others within the PNAS journal. He kindly answered my email stating that the debate of the impact hypothesis is far from over. I believe that Dr. Surovelle's concerns aside, and they do require further elaboration on the part of Drs. Kennett, West and Firestone, that there are a large number of other markers that favour the impact hypothesis, please seewebsite http//wwww.bcclimate.com
I don't understand the need for a new explanation. Clovis man killed off all the
large animals, and moved on. At the end there were no large animals in the Americas and no Clovis people.
Our future is not in our stars, but in
ourselves. And as Aristophanes showed,
he whose head is too concerned about stars
may fall down a well. It seems strange for
an astronomer to have to point out this.
But the urge to blame what happens on an
external agency is universal. It is rarely
correct.
Regarding Neville Woolf's comment: I do think that the Clovis (Blitzkreig theory) Is no longer a seriously considered hypothesis. There have been found to be so may holes found in the premise that most scientists exclude it from consideration., Rod Chilton.
Joanne – My MS thesis had very few radiocarbon dates. Further dates have shifted that age model, indicating that the charcoal peak you refer to is not consistent with an event at 12.9 ka. I gave a talk on that work at ESA last August, which the article refers to.