Answer:
Mass extinction occur when the environment is not favourable.
Step-by-step explanation:
Mass extinctions occur on the earth when there is sudden change in the environmental conditions for an organisms that is not good for the survival of that particular organisms so they extinct from the earth surface. The example of mass extinctions are dinosaurs. These dinosaurs were extinct due to change in their environment that decreases the availability of food for them so due to no available food, the dinosaur extinct from the earth.