What are two possible causes of mass extinctions?

Climate change and some asteroid of considerable size that falls on Earth.

Explanation:

Global warming is changing the seasons, for example, spring is appearing many weeks before in certain parts of the world. Not all species can adjust at the same speed and some are in danger of extinction. This phenomenon is known as phenological mismatch. Climate change is happening very fast so that species can adapt.

Another danger of extinction could be a large asteroid, such as the one that caused the extinction of the dinosaurs. An impact of this asteroid would cause huge volumes of sulfur (derived from gypsum) to be fired into the atmosphere, which would cause a global winter that would be catastrophic.