Recent work has revealed a 62 (+/-) 3-million-year cycle in the fossildiversity in the past 542 My, however no plausible mechanism has been found. Wepropose that the cycle may be caused by modulation of cosmic ray (CR) flux bythe Solar system vertical oscillation (64 My period) in the galaxy, thegalactic north-south anisotropy of CR production in the galactichalo/wind/termination shock (due to the galactic motion toward the Virgocluster), and the shielding by galactic magnetic fields. We revisit themechanism of CR propagation and show that CR flux can vary by a factor of about4.6 and reach a maximum at north-most displacement of the Sun. The very highstatistical significance of (i) the phase agreement between Solar north-wardexcursions and the diversity minima and (ii) the correlation of the magnitudeof diversity drops with CR amplitudes through all cycles provide solid supportfor our model. Various observational predictions which can be used to confirmor falsify our hypothesis are presented.
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