Volcanic theory of mass extinctions
Temporarily increased volcanic activity could also have caused some mass extinctions. A short period existed in the history of the Earth during the Phanerozoic when there were enormous outflow floods of lava over extensive areas. For example, approximately 250 million years ago in the area of Siberia, there was an outflow of 2-3 million km3 of lava during less than 1 million years. This turbulent geological event must necessarily have been accompanied by considerable changes in the chemical composition and physical state of the atmosphere and hydrosphere, with a substantial impact on the global weather and subsequently also on the global biosphere (Officer et al. 1987).
Comparison of the time distribution of the greatest outflows of lava and mass extinctions indicated that a great many of them occurred at the same time (Renne et al. 1995; Kerr 1995; Kerr 2000). For example, the formation of lava traps in Siberia occurred at the same time as the period of the greatest known mass extinction at the end of the Permian and the lava traps in India were formed at the same time as the extinction at the end of the Cretaceous. However, in the latter case, it is now thought that this extinction was more probably caused by the impact of a cosmic body. However, it certainly cannot be excluded that the simultaneous occurrence of both catastrophes could have actually been the cause of the mass extinction and the hypothesis that there was a direct causal relationship between the impact of an enormous cosmic body and elevated volcanic activity should certainly not be rejected (Rampino 1987).
Catastrophes of somewhat smaller extent but still sufficiently drastic could be related to explosive volcanism. Some authors (Rampino 2002) have suggested that super-eruptions occurred, on an average, every 50,000 years, with outflow of more than 1000 km3 of lava and more than 1015 tons of microscopic dust and aerosol particles. The destructive effect of such catastrophes, which was felt in changes in the climate even in the most distant parts of the Earth, would, in their extent, correspond to the collision of the Earth with a cosmic body with a diameter of 1 km; however, these catastrophes would occur roughly twice as often. From our selfish viewpoint of the possibility of survival of the human race, it is of fundamental importance that, in contrast to catastrophes caused by comets, where it may well be possible in the future to artificially avoid their pathways, there is apparently even theoretically no way of effectively defending ourselves against a catastrophe caused by the super-eruption of volcanoes.