Causes of extinction

What caused these extinction events? Several hypotheses have been proposed, but very little is known for certain. In many cases the combined effects of multiple changes in temperature and ocean chemistry were probably deleterious to the dominant organisms of the day.

Tectonic events and continental drift over time change the circulation of the world's oceans, with often dramatic effects on temperature, salinity, dissolved oxygen, and perhaps aragonite saturation state.

Rapid sea level rise (and fall) probably also drowned (and stranded) reefs in certain areas.

Extraterrestrial explanations (bolide impacts) have also (more or less successfully) been offered as causes of dramatic and sudden changes in global climate.