Exploring abrupt climate change induced by comets and asteroids during human history

Face-off: PBS moderates on-line debate between proponents and detractors of Younger Dryas cosmic impact

From PBS’ NOVA site on the Clovis Comet:


by Evan Hadingham, NOVA Senior Science Editor

In Megabeasts’ Sudden Death, NOVA reported on a radical new theory that an extraterrestrial impact devastated North America and other regions at the end of the Ice Age. First aired at a conference in May 2007 by a team led by geological consultant Allen West, the theory proposes that a comet or asteroid struck the ice sheets that covered most of Canada around 12,900 years ago. In an alternative scenario, the theory claims that a series of comet or meteor fragments burst in the atmosphere, similar to the Tunguska explosion that devastated a wide area of Siberia in 1908. In either case, according to the theory, the event ignited continent-wide firestorms and led to the extinction of about 35 types of giant animals, or “megafauna,” including mammoths, mastodons, lions, saber-tooth cats, and giant beavers. The event is also claimed to have reduced the populations of early Native American hunter-gatherers known as the Clovis people, and to have helped flip the Earth’s climate into a severe, final cold phase known as the Younger Dryas.

From its first announcement, the Younger Dryas impact theory sparked widespread controversy among archeologists, astronomers, and the science press. NOVA helped support an attempt to test the theory by a leading climate scientist, Paul Mayewski of the University of Maine, who searched for evidence of distinctive materials associated with impacts in the Greenland ice sheet. As shown in the program, West’s team analyzed Mayewski’s samples from Greenland and their results appeared to confirm the theory.

About a year after the first broadcast of NOVA’s show, several prominent astronomers and physicists who specialize in impact studies and are skeptical of the theory contacted NOVA. They argued that viewers needed to understand one of their key arguments—that an impact of the scale and type envisaged by West’s team was extremely improbable. In NOVA’s program, Sandia Lab physicist Mark Boslough briefly mentions this argument, but the reasoning behind it was not explained. NOVA therefore invited Boslough and astronomer Alan Harris of the Space Science Institute to write brief, non-technical essays about the improbability argument and other objections to the theory. To respond to these points, NOVA askedAllen West and one of his team, retired NASA impact specialist Ted Bunch, to respond to Boslough and Harris’s criticisms. The result is a snapshot of a highly intriguing debate that remains unresolved.”

Go to Evan Hadingham’s original essay of March 2009

Go to Evan Hadingham’s update of May 2011


Go to Alan Harris essay

Go to Mark Boslough essay


Go to Allen West essay

Go to Ted Bunch essay

6 Responses

  1. George,
    great post! I read parts of one totally delightful essay and plan to read more.

    Would it be possible to invite rebuttals for selected individual entries?? Here is why:

    Unfortunately, I have become totally prejudiced against certain well-known individuals who actually have my very high esteem, except that I find it difficult not to smell their prejudice. If a rebuttal is available, then reading the original opinion becomes more palatable. This is similar to putting tabasco sauce on slightly gamy meat,

  2. My G*d what a pack of retards.

    There was no “Clovis People” in the sense of a unified ethnic group.

    “Clovis” was a point technology rapidly adopted by many different peoples. A very good example of cultural diffusion, in fact.

  3. What is bizarre is that data from the Moon is used to estimate Earth impact rates, while Earth impact data is conveniently not gathered, ignored, or suppressed.

    Even for the geologically recent past where we have large craters, what hit is not known.

    Earth-Moon is a 2 body system. We don’t know if the Earth and Moon were impacted at the same rate, or if the Moon took some of the hits for Earth, or if the Earth took some of the hits for the Moon.

    I’d go with option 3, based on the way Jupiter takes cometary impacts.

    I could go on about the spectral sensors and analysis of data sets for other planets, but instead just let me state that in my opinion NASA’s Ed Weiler needs to be “relieved”, as this is the only way that any NASA co-ordination on this hazard with other federal agencies will be possible.

  4. Ed,
    interesting comments there all of it. Would you suggest that the Shoemaker-Levy/9 was an accidental discovery that happened to be a first but that there were many other Jupiter cometary impacts like it at earlier times that escaped human notice simply because we didn’t have a space telescope and fewer/ smaller/ or no Earth-based ground telescopes in pre-Galileo times?

    My guess, after reading your comment, is that Chinese and European naked-eye observers might have missed dozens of comet impacts on Jupiter while observing the night skies in those early days.

  5. Ed – Good and very informed comments, as usual. Weiler must be a real prat.

    Hermann – Your guesses about S-L/9 are good ones, IMHO. My first impression is that they simply weren’t looking before. We don’t have any telescope trained on Jupiter, as a matter of course, do we? And if a lesser number of fragments had hit in a shorter amount of time, it seems they could have fallen in between the cracks (literally in between those windows of observation). I am addressing recent times, of course. In older times, a billion large impacts could have taken place in historical times, and no one would ever have known.

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