The main causes of the disasters that cause mass extinctions seem to come either from above, in the form of deadly asteroids or comets, or from below, in the form of extreme volcanic activity.
a. true
b. false

The answer is True

If you meant only natural disaster, indeed the mass extinctions usually comes from those two factors.

The Permian-Tirassic which killed about 95 % of living organism are caused by a huge Meteor that came to earth.

Or in 2006,  a Tsunami which caused by underground tectonic activity killed hundred of thousand people in Indonesia

17.73 . . . .. .