Interaction of the reasons for the mass biota extinctions in the Phanerozoic

The consideration of the conditions during the mass extinctions has shown that a series of factors, including mutually independent tectonic movements, variations in the sea level and climate, volcanism, asteroid impacts, changes in the composition of the atmosphere and hydrosphere, the dimming of the atmosphere by aerosols at volcanism and impact events, etc., had a harmful affect during some periods of time (a hundred thousand years to millions of years). Some of the listed events occurred for a long period of time and could not have caused the abrupt catastrophic death of organisms on a global scale. The examination of the hierarchy of the major events allows us to distinguish the primary terrestrial (volcanism) and cosmic (impact events) reasons for the mass extinctions. The coeval mutually independent events testify to the common external reasons for the higher order beyond the solar system. These events are suggested to be related with the orbital movement of the solar system around the galaxy's center, the intersection of the galactic branches, and the oscillations of the solar system's position relative to the galactic plane. These reasons influence the processes on the Earth, including the internal and external geospheres, and activate the impacts of asteroids and comets. Under their effect, two main subsequences of events are developed: terrestrial, leading to intense volcanism, and cosmic impact events. In both cases, harmful chemical elements and aerosols are vented to the atmosphere, thus resulting in the greenhouse effect, warming, the dimming of the atmosphere, the prevention of photosynthesis, the ocean's stagnation, and anoxia with the following reduction of the bioproductivity, the destruction of the food chains, and the extinction of a significant part of the biota.