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Re: Crashing Comets Not Likely The Cause Of Earth's Mass Extinctions

At http://dml.cmnh.org/2009Aug/msg00016.html , Dr, Thomas R. Holtz wrote:

>B tH wrote:
>>So, if not an extra-terrestrial impact, what caused the Permian
>> extinction?  Dan from "Roseanne" in "When Dinosaurs Roamed 
>>North America" assured us a comet broke up into five pieces 
>>and smushed us way back then.  ...text deleted....
>The Permian extinction is almost certainly causally related to 
>the Siberian Traps volcanism, although which of the multitude 
>of catastrophes generated by it (if ony one) was most significant 
>is unclear. See recent books by Benton and by Erwin (among 
>others) for good general reviews.

PDF files of various papers on this subject can be found in a previous 
post, " PDF Files of Papers About the terminal Permian Extinction 
Event(s)" at http://dml.cmnh.org/2009Jul/msg00217.html .

A recently published summary paper about the involvement of 
the Siberian Traps volcanism in the Permian extinctions is:

Saunders, A., and M, Reichow, 2009, The Siberian Traps and 
the End-Permian mass extinction: a critical review. Chinese 
Science Bulletin. Vol. 54, no. 1, pp. 19-37.


Also, there is:

Retallack, G. J., and A. H. Jahren. 2008. Methane release 
from igneous intrusion of coal during Late Permian extinction 
events. Journal of Geology. Vol. 116, pp. 1-20.


Other related papers are:

Gastaldo, R. A., J. Neveling, C. K. Clark, and S. S. Newbury, 
2009, The terrestrial Permian-Triassic boundary event bed is 
a nonevent Geology. vol. 37, no. 3, pp. 199-202, doi:10.1130/G25255A.1


Payne, J. L. and L. R. Kump, 2007, Evidence for recurrent Early 
Triassic massive volcanism from quantitative interpretation of carbon 
isotope fluctuations. Earth and Planetary Science Letter


Knoll, A.H., Bambach, R.K., Payne, J.L., Pruss, S., and Fischer, W. 
2007. Paleophysiology and end-Permian mass extinction. Earth and 
Planetary Science Letters. vol. 256, pp. 295-313.


>>That and there seems to be very good evidence of super-craters 
>>for that time period.

>On if by "good evidence" you mean "essentially no evidence"....
>No iridium spike; buckyballs alleged to have extrasolar (!?!) isotopic
>composition; a "crater" under glacial ice which is not confirmed by 
>any real evidence nor dated by any means.

There is no credible evidence of supercraters. There are only the highly 
disputed and controversial Bebout High and Wilkes Land 2 structures. 

Both their location and summary of information about them can be 
Found in the 2009 SEIS impact database at http://impacts.rajmon.cz/ ,
http://impacts.rajmon.cz/IDdata.html , and http://impacts.rajmon.cz/data/ .

About the proposed Wilkes Land 2 structure, the 2009 SEIS impact 
Database states:

"von Frese et al. (2006) reported gravity high in the GRACE 
satellite data 320 km in diameter centered in a circular ridge 
480 km in diameter defined by satellite radar data. They 
estimated the age of the feature at ~250 Ma without any 
reasoning. Wide uncertainty is therefore assigned here 
between 100 Ma (rifting, last continental scale crustal event 
in that part of Antarctica) and ~2.5 Ga (age of appreciable 
amount of crust on the Earth)"

Besides the lack of any hard data confirming the either age or impact 
origin of this feature, there is a lack of any significant presence of the 
accumulation of impact ejecta in outcrops of the Permian-Triassic 
boundary in Australia, New Zealand, and Antarctica, unlike similar 
layers found at the Cretac
 over the 
world from the significantly smaller Chicxulub impact. In my
opinion, this discredits this feature as being the Permian-Triassic impact. 
This lack of any credible and reproducible reports of significant
occurrences of impact debris at the Permian-Triassic discredits any
theory about the proposed impact origin of the extinctions associated
with it.

About the proposed Bedout (High) structure, the 2009 SEIS impact 
Database states:

" Data from (Becker et al., 2004b). The report generated several 
heated comments (Glikson, 2004; Renne et al., 2004; Wignall et 
al., 2004) and responses (Becker et al., 2004c, d; Becker et al., 
2004a). Also discussed by (Gorter, 1998). (MÃller et al., 2005) 
rejected impact hypothesis based on structural study of seismic 
data and suggested two stage rifting explanation for the structure. 
(Becker et al., 2006) reported extraterrestrial Cr from Bedout 
and Graphite Peak P/Tr boundary"

The identification of this structure as an impact structure is at this time is 
highly controversial and questionable. Again, there is no evidence of any 
significant occurrence of impact ejecta, unlike the case of the Cretaceous-
Paleocene boundary, at outcrops of the Permian-Triassic boundary from 
this alleged impact crater. For more discussion of this, go read the published
literature that includes

Retallack, G. J., A. Seyedolali, E. S. Krull, W.T. Holser, C. A. Ambers, 
and F.T. Kyte, 1998, Search for evidence of impact at the Permian-
Triassic boundary in Antarctica and Australia. Geology. Vol. 26, no. 11, 
pp. 979-982.


Isbell, J.I., R.A. Askin, and G.J. Retallack, 1999, Search for evidence 
of impact at the Permian-Triassic boundary in Antarctica and Australia â 
comment and reply. Geology, vol. 27, no. 9, pp. 859-860. 


Krull, E.S., G.J. Retallack, H.J. Campbell, and G.L. Lyon, 2000, 
?13C org chemostratigraphy of the Permian-Tri
 Group, New Zealand: evidence for high latitude methane 
release. New Zealand Journal of Geology and Geophysics. Vol. 43, 
pp. 21-32.


Retallack, G.J., A.H. Jahren, N. D. Sheldon, R. Chakrabarti, C. A. 
Metzger, and R.M.H. Smith, 2005, Permian-Triassic boundary in 
Antarctica. Antarctic Science. vol. 17, no. 241-258.


Retallack, G.J., T. Greaver, and A.H. Jahren, 2007, Return to Coalsack 
Bluff and the Permian-Triassic boundary in Antarctica. Global and 
Planetary Change. vol. 55, pp. 90-108.


Retallack, G.J., E.S. Krull, and S.E. Robinson, 1998, Permian and Triassic 
paleosols and paleoenvironments of the central Transantarctic Mountains, 
Antarctica. U.S. Antarctic Journal. Vol. 31, no. 2, pp. 29-33.



Paul V. Heinrich
Baton Rouge, LA 70803