As America celebrates its Independence Day, I’m thinking not only of the fireworks in store for tonight but also those that may have lit up northern Canada almost 13,000 years ago. The case for an asteroid or comet impact there has been strengthened by work in Ohio and Indiana that examines an unusual fact: Gold, diamonds and silver found in the region owe their origins to the diamond fields of Canada. Did glaciers bring these deposits, which evidently arrived in the same period as the supposed impact, much further south? Or is geophysicist Allen West correct in flagging them as the signs of an ancient catastrophe?
Ken Tankersley, an anthropologist at the University of Cincinnati, doubted West’s notion and opted for the glacier theory until his recent work on the deposits. Says Tankersley:
“My smoking gun to disprove (West) was going to be the gold, silver and diamonds. But what I didn’t know at that point was a conclusion he had reached that he had not yet made public — that the likely point of impact for the comet wasn’t just anywhere over Canada, but located over Canada’s diamond-bearing fields. Instead of becoming the basis for rejecting his hypothesis, these items became the very best evidence to support it.”
Although hardly conclusive, the timing of the event is interesting. The impact would have occurred at a time when the wooly mammoth population disappeared, along with the Clovis culture, a prehistoric civilization that flourished around the end of the last glacial period. The so-called Younger Dryas event caused an extension of ice age conditions at that time, one that could be consistent with the kind of impact West is talking about. I see that TV producers galore — PBS, the History Channel, the Discovery Channel and the National Geographic channel — have zeroed in on Tankersley’s work, including these studies, so expect to hear a good deal more about the Younger Dryas soon.
An earlier Centauri Dreams discussion is here. And be aware of Firestone et al., “Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas,” Proceedings of the National Academy of Sciences 10.1073/pnas.0706977104 (27 September, 2007). Abstract online.
Addendum: Tim Jones digs deeply into this story on his remote central site. Good job! Also see this University of Cincinnati news release.
Related: The 61st Carnival of Space offers a number of weblog takes on the Tunguska event, whose anniversary came last week.
A very good book on this topic is “Barren Lands” by Kevin Krajick. It follows the hunt for diamonds in North America, with a particular emphasis on the glacial propagation of diamonds from the kimberlite pipes in the Northwest Territories. If we can believe the story in this book, the evidence for glacial propagation is strong, and indeed was used to locate the pipes.
It would be interesting to see if this competing comet impact theory can better explain the distribution of surface finds of stray diamonds throughout Canada and the northern US.
I suspect the case for glaciation moving some of these materials is robust, and thanks for the Krajick reference, Ron. Interesting that the case for an impact in such a relatively recent era is still so ambiguous and subject to revision, if indeed the event happened at all.
I think I was a bit too brief in my earlier comment, and this subject seems to be getting a lot of media play. For example:
http://www.universetoday.com/2008/07/07/exploding-asteroid-theory-gains-evidence/
So I decided to elaborate a bit, by summarizes some points of relevance from the book. The first problem the diamond prospectors had was deciding which stray diamond finds were carried to the site and which were native to the site. They wasted lots of time figuring this out. Once they tentatively sorted that out they needed to find the source of the diamonds.
North America is big, really big. Not only that, glaciation covered some or most of the continent over many distinct glacial periods. Since the dominant flow was south they kept looking more northerly hoping to get a better handle on the trajectory of the diamonds. They traced the flow by taking an obscenely large number of mineral samples from all over and processing the slurry to find evidence of minerals uniquely associated with kimberlite pipes, and especially with those pipes associated with diamonds (apparently only a fraction of pipes contain diamonds in commercial quantity and quality).
The thing about glaciers is they are very good abrasives and transporters of debris. However that transport is only one way. As the glacier ‘recedes’ it drops the debris wherever it got to. Therefore (to cut to the chase), they were looking for a clear transition between samples containing evidence of pipe minerals in otherwise non-kimberlite areas and no such minerals. Sort of like following a polluted river upstream until the water runs clean, then reverse course and test every tributary for pollutants.
They found that line after years of work. Then they had to narrow down the search for the pipe, stake it, and … the rest is mining history.
For our purposes I think the key is that there is such a line. Glaciation events, one or many, cause such a line. An impact crater due to a comet or asteroid would litter the kimberlite minerals more isotropically. That was not found.
If there were such an impact it would have to have occurred before the most recent glacial period since any isotropically distributed debris could only then be ‘cleaned up’ by the glaciers to match the present day data.
Keep in mind I am only paraphrasing another’s story. I am no expert in these matters and I have not read any of the relevant scientific papers. I have no idea if West or anyone else considered and addressed this point.
Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event
Authors: Adrian L. Melott (Kansas), Brian C. Thomas (Washburn), Gisela Dreschhoff (Kansas), Carey K. Johnson (Kansas)
(Submitted on 6 Jul 2009 (v1), last revised 1 Oct 2009 (this version, v2))
Abstract: We estimate atmospheric chemistry changes from ionization for the 1908 Tunguska airburst event, finding agreement with nitrate enhancement in GISP2H and GISP2 ice cores, noting an unexplained accompanying ammonium spike. We then consider the candidate cometary impact at the onset of the Younger Dryas (YD).
The estimated NOx production and O3 depletion are large, beyond accurate extrapolation, but the ice core peak is lower than predicted, possibly because of insufficient sampling resolution. Ammonium has been attributed to biomass burning, with a coincident nitrate spike found at YD onset in both GRIP and GISP2 ice cores.
A similar result is well-resolved in Tunguska ice core data, but that forest fire was far too small to account for this. Direct input of ammonia from a comet into the atmosphere is adequate to explain ice core data at the YD event, but not Tunguska data.
An analog of the Haber process with hydrogen contributed by cometary or surface water, atmospheric nitrogen, high temperatures, pressures, and the possible presence of catalytic iron from a comet could in principle produce ammonia, accounting for the peaks in both sets of ice core data.
Comments: Accepted for publication in Geology. Numerous minor revisions in wording; no change in conclusions
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Geophysics (physics.geo-ph)
Cite as: arXiv:0907.1067v2 [astro-ph.EP]
Submission history
From: Adrian Melott [view email]
[v1] Mon, 6 Jul 2009 18:35:53 GMT (101kb)
[v2] Thu, 1 Oct 2009 20:03:10 GMT (133kb)
http://arxiv.org/abs/0907.1067
October 7, 2009
Pictures and Videos Capture Canadian Fireball from Sept. 25, 2009
Written by Nancy Atkinson
A brilliant fireball seen over Ontario, Canada on September 25, 2009 was captured by seven all-sky cameras of the University of Western Ontario’s Southern Ontario Meteor Network (SOMN.) The fireball was seen widely by observers throughout southern Ontario and adjacent areas.
The fireball was first detected by Western’s camera systems at an altitude of 100km, and moving southeastwards at 20.8 km/s. From the data collected, the researchers believe the meteoroid was initially about a meter wide, or about the size of a child’s tricycle. At its brightest, the fireball was approximately 100 times as bright as the full moon.
Full article and video here:
http://www.universetoday.com/2009/10/07/pictures-and-videos-capture-canadian-fireball-from-sept-25-2009/