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An Asteroid Strike in North America?

Earth’s geological history could have a lot to say about our future in space. Every time we investigate a huge crater like Chicxulub, the Yucatan impact site that may have played a role in the demise of the dinosaurs, we’re reminded that the Solar System is an active and dangerous place. And the evidence multiplies. The Wilkes Land crater in east Antarctica may bear witness to the Permian-Triassic extinction that destroyed almost all life on Earth some 250 million years ago.

A defensive system in space with the capability of deflecting dangerous Earth-crossing objects is vital for species survival, whether the next strike occurs in ten or a hundred thousand years. But it’s a hard concept to sell because Earth’s major strikes, unlike those on the Moon, for example, tend to be obscured over time. Absent a visible historical context, a relatively minor strike like the 1908 Tunguska event can come to be seen as a quirky accident rather than evidence of a larger threat.

Now comes word of an explosion over or into the Laurentide ice sheet north of the Great Lakes some 13,000 years ago, causing the extinctions of big mammals like the mammoth and the mastodon by triggering a round of climatic cooling. Here again we have no obvious crater to look at, but rather layers of sediment drawn from numerous sites around the North American continent. In the sediments, a team led by James Kennett (UC Santa Barbara) found amounts of iridium and specks of nano-diamond, along with small spheres of glass and carbon. All that adds up, says the research team, to an explosion 12,900 years ago.

The BBC does a good job covering this story, with this quote from Kennett on the extinctions:

“All the elephants, including the mastodon and the mammoth, all the ground sloths, including the giant ground sloth – which, when standing on its hind legs, would have been as big as a mammoth …All the horses went out, all the North American camels went out. There were large carnivores like the sabre-toothed cat and an enormous bear called the short-faced bear.”

As to human populations, they would have lived through a 1,000 year period of cooling, an era known as the Younger Dryas whose effects were global and may have influenced the beginning of farming in the Middle East. In North America, the impact on the Clovis people, who hunted mammoths, may have been catastrophic. Such speculations enlivened the American Geophysical Union meeting in Acapulco when presented there last week. Let’s hope they also energize a new round of thinking about what a human presence in space can do to head off future catastrophes.

Comments on this entry are closed.

  • James Nicoll May 30, 2007, 10:56

    Allen West seems to have a taste for the dramatic: his last attempt to explain a relatively recent wave of extinctions involved a supernova.

  • Administrator May 30, 2007, 14:00

    Though in this case West is part of a team of 25 that looks pretty solid to me. They’re listed here:


  • Zen Blade May 31, 2007, 17:37

    Speculation… I read about this article last week. What they attempt to extrapolate goes to far. The link to megafauna extinction is very very thin… And the collapse of early human population is also thin.

    Alternative explanation: Human population hunts megafauna to brink of extinction. Human population loses its primary food source. Human population begins to starve. Human population collapses.

    Unfortunately, I am at a conference right now and don’t have the time to take a closer look at the article, but if we consider man to be like any other predator, our population can be (at least partially) linked to the population of our prey.

    -Zen Blade

  • JD May 31, 2007, 19:52

    Interesting. I’m not sure if their theory is correct but I do note one thing. The mega fauna extinction may have enabled colonization of North America by humans. As an example there was speculation that the top predator of the north, the short faced bear, basically ran down and ate early family bands of humans attempting the land bridge route. By this theory only the demise of this bear permitted the small groups to make the journey, consolidate and expand.

    An impact event, such as postulated, would be an enabler of this tentative theory. Consider also that the mega fauna in Siberia went extinct around the same time. Interesting to ponder but I doubt if anyone will ever get the straight of it. They have yet to determine when human habitation commenced in North America, let alone any events that coincided with it.

  • Administrator May 31, 2007, 21:42

    Interesting points both; thanks Zen and JD. Also to keep in mind here is the Clovis culture itself, which apparently is followed by a much less unified series of hunter-gatherer type cultures. The descendants of Clovis, or another group entirely? Huge imponderables in all this because we know so comparatively little. Intriguig to hear about the short-faced bear and North American colonization, JD.

  • Adam June 1, 2007, 6:33

    There’s an intriguing similarity between the Clovis people’s culture and the slightly earlier Solutrean culture complex in Europe. Could Clovis be European originally? And by “European” I mean what paleoanthropologists call “Old Europe” prior to the expansionist agrarian cultures from the Middle East c. 5,000 BC.

  • Athena June 1, 2007, 15:40

    There is a discussion about the Clovis/Solutrean congruity in Charles Mann’s very interesting book 1491. It is possible, too, that humans came by boat hugging the coasts, rather than over the Bering bridge. That may explain why the civilizations in the geographical middle were more urbanized than those on the edges. This would weaken the short-faced bear argument, though the general impact of an asteroid on large animal populations would still apply.

  • Administrator June 1, 2007, 16:36

    Haven’t read Mann’s book yet, but it’s on my list. What fascinating issues!

  • Zen Blade June 3, 2007, 8:42

    The genetic evidence is fairly solid with regards to where Native Americans came from. I’m not sure if any genetic material from Clovis grave sites (if they exist) has ever been looked at, but the genetics shows that the people in most of the Americas at the time of Colombus came via the land bridge between Siberia-Alaska.

    As for predators like the short-faced bear, interesting read at wikipedia:
    -Zen Blade

  • Athena June 4, 2007, 8:38

    @Zen Blade:

    I am a molecular biologist and well acquainted with Cavalli-Sforza’s work on genetics of migration. So I have no doubt that the original American population groups came from Asia. The only question is whether they all came over the Bering land bridge, or whether they also used sea routes. They could hug the coast from north to south, or even go across. The Polynesians accompished a similar feat without compasses and the Pacific currents favor west to east sailing. The Inuit and Pacific Northwest groups used to be outstanding mariners with their kayak and umiak. So that is not out of the question, nor are the two possibilities mutually exclusive.

    As the saying goes, “scientific theories start as heresies and end as superstitions” (*laughs*). And I’m not talking about craziness such as von Däniken’s Chariots of the Venusians.

  • Adam June 5, 2007, 5:58

    Hi Zen Blade & Athena

    Most of the ancestral populace of the Americas no doubt comes from Asia, but if the Clovis people were devastated by the impactor’s effects and the survivors numbered fewer than the Asian immigrants then the distinctive genetics of the Solutrean/Clovis people would be “flooded” and lost as a distinct population. A similar fate is why any genetic heritage from the Neanderthals (extinct by 27,000 bp?) and Asian Erects (possibly extinct as late as 27,000 bp) has been covered over by the late African heritage – itself springing forth c. 60,000 bp.

    There’s a huge range of histories for individual genes in the human genome, with some families of genes going back a long way in time, so overly dogmatic statements on whose genes are whose is perhaps premature.

  • ljk June 5, 2007, 10:30

    Apparently some natural disaster wiped out almost all of humanity
    in Africa some time back (I don’t recall the exact date at the moment),
    leaving only a few thousand human beings on the whole planet. Yet
    our ancestors recovered and now there are 6.7 billion of us on Earth,
    with a couple in near space.

  • Zen Blade June 5, 2007, 11:28


    I agree in principle on the Polynesian boat migrations. Did you know that they spread as far as Madagascar in the west. The largest current ethnic group on Malaysia has origins in Indonesia (based upon language). The culture of travelling from island to island apparently developed because founders of new colonies or towns were essentially treated like royalty. Thus, there was a huge incentive to continually search for new land to colonize.


    I’m going to have to disagree with you about the “flooding out” concept. Male descendents from a male (of group B) would have a VERY VERY different Y chromosome. And any continued line of females would have the same mitochondrial DNA, which would be noticeably distinct. As for other markers, maybe–maybe not.

    -Zen Blade

  • Zen Blade June 5, 2007, 15:03

    Sorry, I just saw a typo.
    “Malaysia” should be “Madagascar”.
    The Austronesian people were quite mobile.
    -Zen Blade

  • Adam June 5, 2007, 16:01

    Hi Zen Blade

    I had heard that about the Madagascans – fascinating! I’m a resident of Sahul, so I’m just next door to all the Sundans. Our own native peoples have some intriguing similarities with the Andaman Islanders – a Murri friend of mine met a few one time and felt a real kinship.

    As for the “flooding” (wish I could remember the correct term) it’s not such a strange thing, nor incompatible with the Y chromosomal lineage – which, after all, is a statistical thing. Combinatorial explosion means that detailed genetic studies require sampling of the possible histories for genes and gene families, so the conclusions aren’t as hard-and-fast as you might think.

    Larry, the human populational bottle-neck was roughly 70,000 bp, roughly the same time as the Toba volcanic detonation that chilled the Earth – thus the theory that it almost caused the extinction of the human race.

  • Zen Blade June 6, 2007, 15:33

    Interesting article in nature today about the presence of chickens in South America


    Essentially, genetic evidence indicates that the birds may have come with polynesians. The authors point out that this does NOT mean that polynesians colonized South America. This simply means there was contact between the groups of people and perhaps trade.

    -Zen Blade

  • James Nicoll June 6, 2007, 23:19

    It’s a pity you are on the wrong side of the US to attend this:


  • James Nicoll June 6, 2007, 23:20

    Hrm. That was supposed to also mention that he was giving a talk at noon at Berkley about his paper.

  • James Nicoll June 6, 2007, 23:27

    “Apparently some natural disaster wiped out almost all of humanity
    in Africa some time back (I don’t recall the exact date at the moment),
    leaving only a few thousand human beings on the whole planet. ”

    Are you thinking of Toba (Big Indonesian volcano, blew about 2,500 km of material into the air, deposited a half a foot of ash across the next subcontinent over and left a ding so large – 100 km x 20 km – that it wasn’t immediately obvious that it was a volcanic remnant)? That was about 74,000 years ago and is in the running for the largest eruption of the last two million years.

  • Administrator June 15, 2007, 15:10

    YouTube offers the press conference on the North American impact story here:


  • ljk June 13, 2008, 16:47

    Next on NOVA: “Mystery of the Megavolcano”


    Tuesday, June 17 at 8 p.m.

    (Check your local listings as dates and times may vary. Broadcast in
    high definition where available.)

    NOVA joins four scientists in their global pursuit of clues to a
    massive volcanic eruption that appears to have had a devastating
    impact on the Earth 75,000 years ago. And if they’re right, the
    ancient supervolcano — and others like it — may someday reawaken,
    with catastrophic consequences for our modern world. Now, an array of
    clues — scattered ashes and ice cores, tiny ocean creatures and
    steaming lakeside rocks — are brought together to solve the “Mystery
    of the Megavolcano.”

    Here’s what you’ll find on the companion Web site:

    The Next Big One


    What could we expect if a supereruption were to occur today?

    Why Toba Matters


    NASA’s Drew Shindell reflects in this interview on the lessons we
    can learn.

    A Supersized Volcano


    As this interactive shows, Toba’s upheaval dwarfs all eruptions
    of recorded history.

    Blasts From the Past


    Explore a map of supereruptions around the world.

    Also, Links & Books, the Teacher’s Guide, the program transcript,
    and more:


  • Jami Nielsen December 3, 2008, 17:56

    I saw James Kennet’s presentation on these discoveries here at University of California, Santa Barbara, only a few monthes ago. And I must say, although controversial, his arguments and quantitative data were very convincing!!
    This article does not do the data justice.
    Zen Blade mentions: “Alternative explanation: Human population hunts megafauna to brink of extinction. Human population loses its primary food source. Human population begins to starve. Human population collapses.”

    -I wish I could quote James Kennet’s explanation of why this was impossible, but I can say with some certainlty humans were NOT the cause of mass megafauna extinctions in N. America. Just very imporbable on that kind of scale!