Causes of mass extinction of sea organisms at the Paleozoic-Mesozoic boundary

At the end of the Permian, at the Paleozoic-Mesozoic boundary (251.0 ± 0.4 Ma ago), 96% of oceanic organisms became extinct. The extinction lasted three million years, but the most intense and abrupt event was 251.4 Ma ago. A series of more or less substantiated hypotheses was suggested to explain this catastrophe: anoxia, higher CO2 and H2S contents, fall of the sea level, volcanism, and impact events confirmed by several impact craters. The synchronous variation in many factors responsible for biodiversity reduction, including those without casual relations, proves the existence of a common cause of primarily cosmic origin.