HR: 1340h
AN: B33C-0271    [Abstracts]
TI: Profound 62 Myr Cycle in Fossil Diversity
AU: * Muller, R A
EM: ramuller@lbl.gov
AF: Department of Physics, University of California, Berkeley, CA 94720 United States
AU: * Muller, R A
EM: ramuller@lbl.gov
AF: Lawrence Berkeley National Laboratory, Mialstop 50R5032 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Rohde, R A
EM: rarohde@lbl.gov
AF: Department of Physics, University of California, Berkeley, CA 94720 United States
AU: Rohde, R A
EM: rarohde@lbl.gov
AF: Lawrence Berkeley National Laboratory, Mialstop 50R5032 1 Cyclotron Road, Berkeley, CA 94720 United States
AB: By combining the Sepkoski Compendium of Marine Fossil Genera with the new ICS 2004 geologic time scale, we have shown that the fossil record contains a 62 +/- 3 Myr cycle in the diversity of genera. This cycle has a very high statistical significance and while the associated changes in diversity are frequently gradual, all of the sharp drops known as major mass extinctions have occurred during declining phases of this cycle. This suggests that the timing or magnitude of these extinctions has been influenced by this periodic process; however, it remains unclear whether extinction events actually cause the cycle. While, we cannot explain the origin of the 62 Myr cycle, we believe it indicates a profound influence of some periodic physical process on Earth's environment throughout at least the last 540 Myr. In addition, the diversity data contain a statistically ambiguous 140 +/- 15 Myr cycle which could be due to changes of the same frequency reported in climate and cosmic rays. While all major mass extinctions seem to bear some relation to this cycle, we also find that the Permian-Triassic extinction was qualitatively unique. This extinction, the most severe in Earth's history, had substantial impact on classes of organisms that were historically resistant to the 62 Myr changes. This suggests that the processes leading to the P-T extinction may have included factors that were unique to that point in the Phanerozoic. It should be noted that the 62 Myr hypothesis is originally due to Thomson (Thomson KS, Nature 261, 578-580 (1976); Devs. in Palaeo. and Strat. 5, 377-404 (1977)) and Ager (Ager DV, Proc. Geologists' Assoc. 87, 131-159 (1977)), though their work has largely been forgotten. At the time of this submission, our revival of the 62 Myr hypothesis and related analysis is currently undergoing peer review at Nature.
DE: 1035 Geochronology
DE: 1600 GLOBAL CHANGE (New category)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting