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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
"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
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
About the proposed Bedout (High) structure, the 2009 SEIS impact
" 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,
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,
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