No Impact


The following was posted on the Cambridge Conference Network (24 September 1999).

No Evidence for Climate-Perturbing Cosmic Impact Around 4000 BC
Doug Keenan <doug.keenan@virgin.net>

There is very strong evidence for a climatic upheaval c. 4000 BP. The big question is "what caused the upheaval?" Many seem to believe that the cause was a cosmic impact. I would prefer to not consider the cause right now. Instead, I would like to consider a smaller, related, question: is there evidence specifically for a climate-perturbing cosmic impact c. 4000 BP? (Please note that this is different from asking if a cosmic impact can explain the available palaeodata.) What follows reviews the evidence that I have seen presented.

[079] The date is tentatively c. 2900 BC, by thermoluminescence (in Utah).
[157] (i) Dates made in the 1960s--thus ranging over many centuries; the event was not an earthquake, but a gradual uplift (on E coast of N America). (ii) Date accuracy not reported; the event was a gradual subsidence (Veracruz, Gulf of Mexico). As Peiser notes, these two events appear to be due to a gradual differential warping (of the N American plate).
[162] The date is ~3400 (14C) BP, and almost certainly after 1900 BC.
[182] Large and at about the right time (in Fiji).
[185] The date is almost certainly before 3750 BC.
[213] The date is almost certainly after 1650 BC.
[302] The date is roughly 2900 BC; the event was not an earthquake, but a gradual emergence.

(Note - refs 079 and 157 were unavailable to me; I have depended on Peiser.) The above events do not constitute evidence for a cosmic impact c. 4000 BP.

This obviously does not mean that there wasn't a climate-perturbing cosmic impact c. 4000 BP. I believe, though, that there is no evidence available specifically for such an event.

Cheers, Doug Keenan

References
Courty, M.-A. "The Soil Record of an Exceptional Event at 4000 B.P. in the Middle East", Natural Catastrophes During Bronze Age Civilisations (editors--Peiser, B. J., Palmer, T. & Bailey, M. E.) 93-108 (British Archaeological Reports [Archaeopress], Oxford, 1998).

Keenan, D. J. "The three-century climatic upheaval of c. 2000 BC, and regional radiocarbon disparities", Los Alamos Archives: Physics/9908052 (1999). [Also available at http://freespace.virgin.net/doug.keenan .]

Peiser, B. J. "Comparative Analysis of Late Holocene Environmental and Social Upheaval", Natural Catastrophes During Bronze Age Civilisations (editors--Peiser, B. J., Palmer, T. & Bailey, M. E.) 117-139 (British Archaeological Reports [Archaeopress], Oxford, 1998).

Schultz, P. H. & Lianza, R. E. "Recent grazing impacts on the Earth recorded in the Rio Cuarto crater field, Argentina", Nature 355: 234-237 (1992).

Weiss, H. & six others. "The Genesis and Collapse of Third Millennium North Mesopotamian Civilization", Science 261: 995-1004 (1993).

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