25 Mya to 20 Mya
25,000,000 BP: what we have called the Laramide Revolution shook the Earth. It raised what is now the US state of New Mexico from below sea level to above sea level and so began a period of volcanism.
20.44 Mya, Burdigalian: Orogeny in northern Hemisphere. Start of Kaikoura Orogeny forming S0uthern Alps in New Zealand. Widespread forests slowly draw in massive amounts of CO2 gradually the level of atmospheric CO2.
23.03 Mya, Aquitanian: From a 6500 pmv CO2 level to around 100 ppmv during the Miocene. Modern mammal and bird families become recognizable. Horses and mastodons diverse. Grasses become ubiquitous.