How did life on earth become so diverse?

"Through the Tertiary period (from 65 Ma) the Earth's climate became cooler with frequent oscillations that increased in amplitude and led to a series of major ice ages in the Quaternary. Glacial advances and retreats over the Pleistocene resulted in global cycles of contraction, expansion and fragmentation of species ranges resulting in species extinctions, population bottlenecks and differentiation."

Explanation:

(Did offline will rewrite in my own words if you would like :)

Hope this helps