- Greater then 50% of the species die
- Must happen world wide
- Happens quickly (for geological time)
- Must cross environments
Two major extinctions happen at the end of
the Paleozoic and again at end of the
Mesozoic era.
Causes of Mass Extinction
- Climate change
- Asteroid impact
- Volcano
If an asteroid hits the earth, it could create
enough dust to black out the sun, this would
make the environment cold and dark
Proof of an asteroid hit
Two men were sampling strata (rock layers)
across the KT boundaries (At the 65 million
year mark). Here they found blue clay of
Gubbio, Italy. This sample was rich with
Irridium (which is very rare on earth but
common in asteroids.) They visited other
placed where this KT boundary was exposed
and found more irridum.