Biology
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmpp13c1468i&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #PP13C-1468
Biology
0444 Evolutionary Geobiology, 0473 Paleoclimatology And Paleoceanography (3344, 4900), 1520 Magnetostratigraphy, 4910 Astronomical Forcing, 9615 Permian
Scientific paper
The Permian magnetostratigraphic records demonstrate that a remarkable change occurred in geomagnetism in the Late Guadalupian (Middle Permian; ca. 265 Ma) from the long-term stable Kiaman Reverse Superchron (throughout the Late Carboniferous and Early-Middle Permian) to the Permian-Triassic Mixed Superchron with frequent polarity change (in the Late Permian and Triassic). This unique episode called the Illawarra Reversal probably reflects a significant mode change in geodynamo in the outer core of the planet after a 50 million year-long stable geomagnetism. The Illawarra Reversal was likely led by the appearance of thermal instability at the 2,900 km-deep core-mantle boundary in connection with mantle superplume activity. The Illawarra Reversal and the Guadalupian-Lopingian boundary event recorded the significant transition from the Paleozoic to Mesozoic-Modern world. Major global environmental changes in the Phanerozoic occurred almost simultaneously in the latest Guadalupian, e.g., 1) mass extinction, 2) ocean redox change, 3) sharp isotopic excursions (C and Sr), 4) sea-level drop, and 5) plume-related volcanism. In addition to the claimed possible link between the above-listed various environmental changes and mantle superplume activity, here I propose an extra explanation that a change in the core's geodynamo may have played another important role in determining the surface climate of the planet and the course of biotic evolution. When a superplume is launched from the core-mantle boundary, resultant thermal instability makes the geodynamo's dipole of the outer core unstable, and lowers the geomagnetic intensity. Being modulated by geo- and heliomagnetism, cosmic ray flux from the outer space into the Earth's atmosphere changes along time. The more cosmic ray penetrates through the atmosphere, the more cloud develops to increase albedo, thus enhances cooling the Earth's surface. The Illawarra Reversal, the Kamura cooling event, and other unique geologic phenomena in the Late Guadalupian were all likely caused by the superplume activity that initially triggered the breakup of Pangea. The secular change of cosmic radiation may explain not only the extinction-related global climatic changes in the end-Guadalupian but also the long- term global warming/cooling trend in Earth"fs history in terms of cloud coverage over the planet.
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