' University of Kansas Space Physics

University of Kansas


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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 solar 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 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 northward excursions and the diversity 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.

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Last modified November 11, 2011
Tizby Hunt-Ward