Evidence Against Permian-Triassic Asteroid Impact Published
Paul bristolia at yahoo.com Wed Dec 12 16:21:26 EST 2007
In “December Media Highlights: Geology and GSA Today” at:
http://www.geosociety.org/news/pr/07-68.htm, there is:
Xie, S., R. D. Pancost, J. Huang, P. B. Wignall, J.
Yu, X. Tang, L. Chen, X. Huang, and X. Lai, 2007,
Changes in the global carbon cycle occurred as two
episodes during the Permian-Triassic crisis. Vol. 35,
no. 12, pp. 1083-1086.
http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FG24224A.1The press release stated:
“Earth witnessed its most severe mass extinction 250
million years ago. This extinction has been thought
to be abrupt and probably caused by an extraterrestrial
impact. However, Xie et al. present several lines of
geochemical evidence from a South China section (an
optimal section to study the biotic crisis) that
indicates a two-episodic global change in association
with the ecological crisis. The global carbon cycle,
the enhanced terrestrial weathering, the marine
photic zone euxinia, the faunal mass extinction,
and the cyanobacterial expansion all occurred as two
episodes, showing a close coupling among the ocean,
the atmosphere, and the land system at that time. In
particular, Xie et al. found that the first episode
occurred before the presumed bolide impact. The
temporal sequence of these two events suggests that
the biotic crisis was a consequence of prolonged and
episodic changes in the marine and continental
systems, and argues against an extraterrestrial
impact as the main cause.”
Yours,
Paul H.
