What are some factors that have caused the dominant life-forms on Earth to
change over time?

1) Mass extinctions
-every time Earth has had a mass extinction, it is followed by a rapid evolution of new species
-we lose a lot of species but we also have opportunities for new species
2) Continental drift
-continents don't stay put, move around earth's surface
-when it moves, the climate changes
-the species will have to adapt to the new climate
-best example: Antarctica used to be at the equator