Clovis Comet on BBC and The History Channel

For those who’re still hung up on looking for shock metamorphic effects in the Great Lakes region, ya’ll should pay special attention to Pete Schultz’s ice sheet impact experiments done at NASA Ames Hypervelocity Vertical Gun Range. And that are featured in that video. Those ice sheet impact experiments beginning at about 7:35 into the clip are the very work that was mentioned in the 2007 paper by Firestone et al in the last paragraph of the section titled ‘Nature of The Event’

Those oblique angle experiments into a layer of ice are the “unpublished data” by Pete Schultz they’re talking about.

From Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

“Toon et al. suggest that an impact capable of continent-wide damage requires energy of 10^7 megatons, equivalent to an impact by a 4-km-wide comet . Although an impactor that size typically leaves an obvious large crater, no such late Pleistocene crater has been identified. The lack of a crater may be due to prior fragmentation of a large impactor, thereby producing multiple airbursts or craters. Hypervelocity oblique impact experiments (Peter. H. Shultz , unpublished data) indicate that a low-impedance surface layer, such as an ice sheet, can markedly reduce modification of the underlying substrate if the layer is equal to the projectile’s diameter. These results suggest that if multiple 2-km objects struck the 2-km-thick Laurentide Ice Sheet at 30°, they may have left negligible traces after deglaciation. Thus, lasting evidence may have been limited to enigmatic depressions or disturbances in the Canadian Shield (e.g., under the Great Lakes or Hudson Bay), while producing marginal or no shock effects and dispersing fine debris composed of the impactor, ice-sheet detritus, and the underlying crust.”

If Pete’s ice sheet impact experiments are any indicator, (and they are the only real clues we have of the actual physics of an ice sheet impact) then there is a very high probability that even if the Laurentide Ice Sheet was one of the primary impact zones, no crater, or shock metamorphic effects will ever be found. Indeed if there is any remaining planetary scarring from the YD event anywhere in the region that was covered by the LIS that scarring probably won’t bare any resemblance whatsoever to anything we’ve ever associated with an impact event.

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Pierson Barretto says:

July 8, 2012 at 5:19 pm

Hello folks

Yeah, I still regret that North American scientists are still figuring that the U.S. is the navel of this story. Until when we still have to wait for an understanding of the global phenomenon? It was not a comet but a stream of fragments that reached our planet. I think it should be a cultural issue. Anyway best millimeter forward to this understanding that staying in uniformitarianism. I keep waiting for the newest news. Meanwhile I follow my intuition.

regards
pierson
Dennis Cox says:

July 8, 2012 at 6:19 pm

Yeah I noticed they are still stuck in the single bolide blowing up in the atmosphere paradigm. Apparently no one told them it was most likely already a cluster of fragments before it got here.

But it’s normal for documentaries like that to be two, or three years behind the science.

On the plus side of things, the theory is getting positive airtime.
Dennis Cox says:

July 8, 2012 at 10:59 pm

For those who’re still hung up on looking for shock metamorphic effects in the Great Lakes region, ya’ll should pay special attention to Pete Schultz’s ice sheet impact experiments done at NASA Ames Hypervelocity Vertical Gun Range. And that are featured in that video. Those ice sheet impact experiments beginning at about 7:35 into the clip are the very work that was mentioned in the 2007 paper by Firestone et al in the last paragraph of the section titled ‘Nature of The Event’

Those oblique angle experiments into a layer of ice are the “unpublished data” by Pete Schultz they’re talking about.

From Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

“Toon et al. suggest that an impact capable of continent-wide damage requires energy of 10^7 megatons, equivalent to an impact by a 4-km-wide comet . Although an impactor that size typically leaves an obvious large crater, no such late Pleistocene crater has been identified. The lack of a crater may be due to prior fragmentation of a large impactor, thereby producing multiple airbursts or craters. Hypervelocity oblique impact experiments (Peter. H. Shultz , unpublished data) indicate that a low-impedance surface layer, such as an ice sheet, can markedly reduce modification of the underlying substrate if the layer is equal to the projectile’s diameter. These results suggest that if multiple 2-km objects struck the 2-km-thick Laurentide Ice Sheet at 30°, they may have left negligible traces after deglaciation. Thus, lasting evidence may have been limited to enigmatic depressions or disturbances in the Canadian Shield (e.g., under the Great Lakes or Hudson Bay), while producing marginal or no shock effects and dispersing fine debris composed of the impactor, ice-sheet detritus, and the underlying crust.”

If Pete’s ice sheet impact experiments are any indicator, (and they are the only real clues we have of the actual physics of an ice sheet impact) then there is a very high probability that even if the Laurentide Ice Sheet was one of the primary impact zones, no crater, or shock metamorphic effects will ever be found. Indeed if there is any remaining planetary scarring from the YD event anywhere in the region that was covered by the LIS that scarring probably won’t bare any resemblance whatsoever to anything we’ve ever associated with an impact event.