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

Clovis Comet paper #1 read article in Geology

Restored from the library fire 1/11/20

The wisdom of crowds is comforting. Despite the near total news blackout of the recent developments related to our subject, readers have shot Anders Carlson’s 2010 free paper, What Caused the Younger Dryas Cold Event?, to the top of the Most Read articles in the journal Geology.

I am not surprised. This is an absolutely fascinating subject and normal people are roaming around reading all sorts of things without the filter of someone else at the keyboard.

What makes Carlson’s broadly named journal article interesting is that it is clearly concerned with the Younger Dryas Boundary Hypothesis. He expresses a desire to test it more closely by appropriately examining existing ice records for chemical signals of the event, refering frequently to another objective overview from Melott which I am trying to post as well.

Note Carlson’s paper was written after Surovell et al had supposedly dumped the last shovel of dirt on the body of the hypothesis. It is hard to keep a good theory down these days.


Download the PDF file .

I can’t find a handy Melott paper, but here is good article on the publication just before Sid Perkins turned his back on the subject of the Younger Dryas Boudary:

**I found the paper and added it while recovering other items in this post from the library fire – Marc**

Download the PDF file .

Signs of giant comet impacts found in cores
Copious ammonium may be evidence of a 50-billion-ton strike at the end of the ice age

By Sid Perkins
Web edition: March 30, 2010
A+ A- Text Size
A new study cites spikes of ammonium in Greenland ice cores as evidence for a giant comet impact at the end of the last ice age, and suggests that the collision may have caused a brief, final cold snap before the climate warmed up for good.

In the April Geology, researchers describe finding chemical similarities in the cores between a layer corresponding to 1908, when a 50,000-metric-ton extraterrestrial object exploded over Tunguska, Siberia, and a deeper stratum dating to 12,900 years ago. They argue that the similarity is evidence that an object weighing as much as 50 billion metric tons triggered the Younger Dryas, a millennium-long cold spell that began just as the ice age was loosening its grip (SN: 6/2/07, p. 339).

Precipitation that fell on Greenland during the winter after Tunguska contains a strong, sharp spike in ammonium ions that can’t be explained by other sources such as wildfires sparked by the fiery explosion, says study coauthor Adrian Melott, a physicist of the University of Kansas in Lawrence.

The presence of ammonium suggests that the Tunguska object was most likely a comet, rather than asteroids or meteoroids, Melott says. Any object slung into the Earth’s atmosphere from space typically moves fast enough to heat the surrounding air to about 100,000° Celsius, says Melott, so hot the nitrogen in the air splits and links up with oxygen to form nitrates. And indeed, nitrates are found in snow around the Tunguska blast. But ammonium, found along with the nitrates, contains hydrogen that most likely came from an incoming object rich in water — like an icy comet.

More than a century after the impact, scientists are still debating what kind of object blew up over Tunguska in 1908. They also disagree about whether an impact or some other climate event caused the Younger Dryas at the end of the ice age. But the presence of ammonium in Greenland ice cores at both times is accepted.

“There’s a remarkable peak of ammonium ions in ice cores from Greenland at the beginning of the Younger Dryas,” comments Paul Mayewski, a glaciologist at the University of Maine in Orono who was not involved in the new study. The new findings are “a compelling argument that a major extraterrestrial impact occurred then,” he notes.

Whenever a comet strikes Earth’s atmosphere, it leaves behind a fingerprint of ammonium, the researchers propose. Immense heat and pressure in the shock wave spark the creation of ammonia, or NH3, from nitrogen in the air and hydrogen in the comet. Some of the ammonium, or NH4+, ions generated during subsequent reactions fall back to Earth in snow and are preserved in ice cores, where they linger as signs of the cataclysmic event.

Although an impact big enough to trigger the Younger Dryas would have generated around a million times more atmospheric ammonia than the Tunguska blast did, the concentrations of ammonium ions in the Greenland ice of that age aren’t high enough.

But the relative dearth of ammonium in the ice might simply be a result of how the ice cores were sampled, Melott and his colleagues contend. Samples taken from those ice cores are spaced, on average, about 3.5 years apart, and ammonia could have been cleansed from the atmosphere so quickly that most of the sharp spike might fall between samples.

Melott, A.L., et al. 2010. Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event. Geology 38(Apr.):355. DOI: 10.1130/G30508.1

13 Responses

  1. Papers finding “consistent with” data and chemistry are necessary, in the long slog until a real impact event is found and vetted. Some (Daulton, etc.) will never be convinced, but objective results like this are stones in the foundation.

    Thanks for finding this, George.

  2. Carlson: “Ultimately, the bolide-forcing hypothesis predicts that the Younger Dryas is a unique deglacial event, as suggested by Broecker (2006).”

    Ed here, for one, will argue the YD isn’t unique, though its “deglacial event” qualities and forcings may be unique (though the YD was, as we and they all know, not a deglaciation event at all). The point being that with other impacts, other ammonia spikes should be in the ice record – if the relatively small Tunguska event is – and to the non-catastrophists these would be used to confuse the ammonia-YD argument.

    On the contrary, this ammonia record may now possibly be used to identify those other (likely Encke progenitor fragment) bolides/impactors in their Holocene periods.

  3. Carlson picked up on this use in his last paragraph, as I read him.

    But I should also extend that “Holocene” period to include the Pleistocene.

    It would, of course, be interesting to see how well those ammonia spikes (when all are identified) line up with Bond Events and D-O Events. One would expect reasonable alignment – enough to predict a correlation, even.

  4. Okay, the Merlott et al abstract was submitted in 2009 and accepted in 2009, but the paper was published in 2010.

  5. Also downloaded from the GSA site:

    Matthew J. Fouch, “The Yellowstone Hotspot: Plume or Not?” (May 2012)

    At issue is the Morgan Mantle Plume theory for Yellowstone:

    Morgan, W.J., 1971, “Convection plumes in the lower mantle“: Nature, v. 230,
    p. 42–43.

    The paper argues against this, similar to the website

    Actually, the hotspot probably resulted from a comet impact in the Modoc Plateau, NE California during the Miocene, 17 Ma BP. There, as caldera was discovered in a Colorado School of Mines MS thesis. Years ago, I happened to come across a GSA abstract by the author and his adviser. The impact is easily recgnized by its rebound, the typical central uplift in the innermost ring in diatomaceous earth, then at the cratonal margin,
    known locally as Chalk Mountain, map coordinates 40.994,-121.809. For the Yellowstone hotspot track leading from the Modoc Plateau, CA, to the present day National Park, WY, see this map:

  6. Thanks, Jenkoul, for a provocative link and duscission.I’m certainly not expert enough to weigh in here on the science itself, but I would think National Geographic would have caught the problem noted by Jack Adler before publishing if Adler’s claim were credible.Adler seems to have a dog in this fight, but he also produces what looks like credible evidence. Still, it doesn’t seem that he publishes in refereed journals or top magazines. Why not?On those grounds, I’m inclined to favor the National Geographic article. Apparently, the sponsors of the researchers also seem to have that inclination since they are talking about sending a team back for a bottom search. That should settle the issue once and for all.I love this kind of duscission, because it illuminates how science unfolds in the real world.Readers, do you have anything to add?Fred Bortz Science and technology books for young readers (www.fredbortz.com) and Science book reviews (www.scienceshelf.com)

  7. I like a good glass of merlot as much as the next guy. And I’m sure Adrian Melott is a fine scientist. But I wouldn’t go so far as to confuse him with a fine wine.

    (Pun intended)

  8. Came upon the following: a disintegration of an asteroid caught by the Hubble telescope. It’s believed two asteroids collided and the debris trail was then created by light pressure on the various fragments and sweeps off to one side of its orbit. It is far more likely that a comet broke apart from an asteroid collision than with another type of object because there are so many asteroids. It’s possible the comet was struck by only a small piece of space debris; not enough to explode it, just enough to shatter it so it broke into many pieces. If a debris trail like this was created it would have provided a far larger target for the earth to plow through than debris trailing a comet in close to the same orbit. The two orbits wouldn’t have had to intersect exactly. http://www.jpl.nasa.gov/images/asteroid/20100203/asteroid20100203-full.jpg

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