Global volcanism, biological mass extinctions and the galactic vertical motion of the solar system

Summary. The recent findings of nearly matching long-term cyclicity in biological mass extinctions, geomagnetic reversals, impact cratering and other terrestrial processes have evoked a major controversy. We report here a compilation and analysis of major global magmatic episodes showing a significant enhancement of volcanic activity with a periodicity of 33 million years for the last 250 million years. These magmatic episodes match extremely well the best available astronomical estimates of the periodic (31 ± 5 Myr) galactic-disc crossing events during vertical motions of the solar system. These events also have a close linkage with the marine biological mass extinctions and other geological rhythms. It is argued that the prolonged volcanic activity, instead of impact cratering, may have been the more immediate primary cause for profound climatic and other environmental deterioration sufficient to create biological crises on a global scale. The volcanic periodicity scheme is well supported by the evidence of recent increases in volcanic activity. However, the alternative hypothesis of the death star 'Nemesis' can be rejected, since it does not explain the recent increase in volcanism and impact cratering during the last 4 ± 3 Myr in view of its quieter apehelion position lying beyond the Oort cloud of comets.