EXCLUSIVE: Comet impact did not kill off early prehistoric culture

Clovis culture was not destroyed by a comet, according to researchers.

February 01, 2013

The end of the 9,000-year-old Clovis culture was not the result of a comet colliding with Earth, according to a newly published report.

Researchers say that they have gathered evidence that shows that a massive comet never impacted near the site of the Clovis society, located in what is now known as New Mexico. The Clovis culture is widely seen as one of the oldest cultures in North America.  Soon after forming (less than 600 years), the society disappeared, leading to speculation that a significant event killed off large portions of the population.

The following is a transcript of our interview with Mark Boslough, a physicist at Sandia National Laboratories and adjunct professor at the University of New Mexico, who co-authored the study. Read our original coverage of the study here.

Science Recorder (SR): Is there any evidence of an impact outside of the immediate area studied? For example, are there any impact sites on Earth that match within the time period in question?

Mark D. Boslough (MB): None that we know about.  The best-preserved impact crater in North America is Meteor Crater, Arizona.  It is about 50,000 years old, which is more than three times older than the putative Younger Dryas boundary impact.   The hypothesis suggests an impactor that had an equivalent explosive energy about a million times greater than the object that blasted out Meteor Crater.   Even the tiniest stray fragment that didn’t explode or hit a thick ice sheet would have had enough energy to make a crater bigger than Meteor Crater, but with only a third the time to erode.  The proponents of the hypothesis have suggested that a possible crater in the Gulf of St.  Lawrence , called Corossol.  This is a circular structure that has neither been dated nor confirmed as an impact crater.  Stratigraphy indicates only that it is younger than Ordovician (about 440 million years old at the top).  So the expected likelihood (if it could be any age in the range of uncertainty) that it has anything to do with the Younger Dryas is almost zero.

SR: What is the single most important takeaway from this study?

MB: From my perspective only…other authors will probably have different opinions.  (I am an impact physicist/geophysicist by training, but also interested in climate change).  Large impacts of the size proposed by the Clovis Comet hypothesis (4 km in diameter) are extremely rare, and the likelihood of one happening now is virtually zero.  Conversely, abrupt climate changes of a magnitude that can trigger an environmental collapse, mass extinction, and human catastrophe are regular occurrences on time scales of tens of thousands of years.   These abrupt climate changes can have relatively small trigger mechanisms such as minute differences in the tilt of the Earth, and increases in atmospheric greenhouse gas concentrations.     Earth’s climate is currently benign and conducive to civilization and agriculture, but it is in a delicate balance.  If we are not careful we run the risk of disrupting that balance.

SR: Does this study provide us with any information for how to prepare for future impacts?

MB: Not in my opinion.  There’s no evidence for an impact, so there’s no information about future impacts.   I am involved with the planetary defense community (those concerned with the threat of impact from comets and asteroids).  I have argued that the smaller asteroids (about 50 to 150 meters in diameter) are in the category that represents most of the impact risk, since nearly all of the large ones (1 km in diameter and larger) have already been discovered and none of them is on a collision course.   The lack of evidence for a significant impact 12,900 years ago is consistent with the extreme low probability of large impact events.

SR: How Clovis culture disappear?

MB: That’s outside my area of expertise.  I will leave it for a coauthor to answer.

SR: Do scientists have a explanation for the period of extreme cooling in question?

MB: The best explanation is a variation on the idea first proposed by Wallace Broecker, that an ice dam collapsed at the end of the last ice age, and fresh water poured into the North Atlantic, slowing down the Gulf Stream and preventing its heat from getting to the north.  Here’s a link to a little article I wrote about it in the context of the impact hypothesis: http://www.csicop.org/si/show/when_scientists_actually_change_their_minds

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