Asteroid and comet impacts are not the only possible
cause for the Permian and Triassic-Jurassic extinctions.
Some recent papers on a likely major contributing cause
to these mass extinctions are:
1. 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. 20-37.
http://www.springerlink.com/content/1743222152769702/
"Compromise of the carbon sequestration systems (by
curtailment of photosynthesis, destruction of biomass,
and warming and acidification of the oceans) probably
led to rapid atmospheric CO2 build-up, warming, and
shallow-water anoxia, leading ultimately to mass
extinction."
2. Knoll, A. H., R. K. Bambach, J. L. Payne, S. Prussa and
Woodward W. Fischer, 2007, Paleophysiology and end-Permian
mass extinction. Earth and Planetary Science Letters.
vol. 256, no. 3-4, pp. 295-313.
http://dx.doi.org/10.1016/j.epsl.2007.02.018
"Global warming, anoxia, and toxic sulfide probably all
contributed to end-Permian mass mortality, but hypercapnia
(physiological effects of elevated PCO2) best accounts
for the selective survival of marine invertebrates."
3. Hautmann, M., 2004, Effect of End-Triassic CO2
maximum on carbonate sedimentation and marine mass
extinction. Facies. vol. 50, pp. 257-261.
http://www.springerlink.com/content/ajvptjvenfvte5ck/
"Besides the frequently cited climatic effect of enhanced
carbon dioxide, lowering the saturation state of sea water
with respect to calcium carbonate was an additional driving
force of the end-Triassic mass extinction, which chiefly
affected organisms with thick aragonitic or high-magnesium
calcitic skeletons. Replacement of aragonite by calcite,
as found in the shells of epifaunal bivalves, was an
evolutionary response to this condition."
4. Hautmann, M., M., J. Benton, and A. Tomasovych, 2008,
Catastrophic ocean acidification at the Triassic-Jurassic
boundary. Neues Jahrbuch fur Geologie und Paleontologie
Abhandlungen. vol. 249, pp. 119-127.
"Using carbon isotopes as a geochemical marker, we found
that the onset of the CO2 emissions coincided with an
interruption of carbonate sedimentation in palaeogeographically
distant regions, suggesting that hydrolysis of CO2 led to
a short but substantial decrease of seawater pH that slowed
down or inhibited precipitation of calcium carbonate minerals.
The cessation of carbonate sedimentation correlates with a
major marine extinction event, which especially affected
organisms with aragonitic or high-Mg calcitic skeletons and
little physiological control of biocalcification."
5. Ryan, D., and D. Lehrann, 2009, Petrographic evaluation of
a Permian-Triassic erosion surface and implications for causes
of the end-Permian mass extinction. Geological Society of
America Abstracts with Programs, Vol 41, No. 4, p. 17.
http://gsa.confex.com/gsa/2009NC/finalprogram/abstract_156104.htm
"Our results favor genesis as a submarine dissolution surface
resulting from ocean acidification during the end-Permian
extinction."
6. Veron, J. E. N., 2008, Mass extinctions and ocean acidification:
biological constraints on geological dilemmas. Coral Reefs.
vol. 27, no. 3., pp. 459-472.
http://www.springerlink.com/content/085g2151l3nlt871/
7. Zhuravlev, A. Y., and R. A. Wood, 2009, Controls on
carbonate skeletal mineralogy: Global CO2 evolution and
mass extinctions. Geology. vol. 37, no. 12, pp. 1123-1126.
http://geology.gsapubs.org/content/37/12/1123.abstract
"Mass extinction events, many of which may be caused by
rapid global changes in temperature and/or pCO2, represent
major intervals of turnover."
8. Sleep, N. H., 2009, End-Permian Extinction From Massive
Basalt-Coal Interaction. Geological Society of America Abstracts
with Programs, Vol. 41, No. 7, p. 359.
http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_162958.htm
"The sudden CO2 and methane release then resulted in strong
global warming. There was insufficient time to renew the
mixed layer of the ocean, resulting in much stronger
acidification than in the present ocean. Overall, changes
that occur over less than the lifetimes of organisms are
more likely to have catastrophic biological effects than slow
changes. Therefore a sudden massive release of CO2 from coal
burning over a few years is a more likely mass extinction
mechanism than the gradual release of CO2 from metamorphism
over 10000s of years in the Siberian basin."
Yours,
Paul H.
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