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Do extragalactic cosmic rays induce cycles in fossil diversity.pdf

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Do extragalactic cosmic rays induce cycles in fossil diversity

a r X i v : a s t r o - p h / 0 6 0 2 0 9 2 v 3 9 A p r 2 0 0 7 Do extragalactic cosmic rays induce cycles in fossil diversity? Mikhail V. Medvedev and Adrian L. Melott Department of Physics and Astronomy, University of Kansas, KS 66045 ABSTRACT Recent work has revealed a 62±3-million-year cycle in the fossil diversity in the past 542 My, however no plausible mechanism has been found. We propose that the cycle may be caused by modulation of cosmic ray (CR) flux by the So- lar system vertical oscillation (64 My period) in the galaxy, the galactic north- south anisotropy of CR production in the galactic halo/wind/termination shock (due to the galactic motion toward the Virgo cluster), and the shielding by galactic magnetic fields. We revisit the mechanism of CR propagation and show that CR flux can vary by a factor of about 4.6 and reach a maximum at north-most displacement of the Sun. The very high statistical significance of (i) the phase agreement between Solar north-ward excursions and the di- versity minima and (ii) the correlation of the magnitude of diversity drops with CR amplitudes through all cycles provide solid support for our model. Various observational predictions which can be used to confirm or falsify our hypothesis are presented. Subject headings: astrobiology — Galaxy: general — shock waves — acceler- ation of particles — diffusion — magnetic fields 1. Introduction Rohde Muller (2005) (hereafter RM) performed Fourier analysis of detrended data from Sepkoski’s compendium (Sepkoski 2002) and found a very strong peak at a period of about 62 My. Monte Carlo simulations based on random walk models with permuted steps reveal a 99% probability that any such major spectral peak would not arise by chance, thus putting the diversity cyclicity on a firm statistical basis. The signal found by RM is robust against changes in procedure to improve aspects of uneven sampling and alternate methods of assessing significance (Cornette 2007; Lieberman Melott 200