After Early Eocene, three steps of global cooling. Fossil Flora Record Fossil plants provide a record of dramatic cooling of Earth's climate after the early Eocene interval of global warmth. Cold, dense polar water began to sink to the deep sea as it does today. Eocene-Oligocene Mass Extinctions Microfossils, especially those adapted to warm conditions. Shrinking of forests led to further cooling, positive feedback .
Forests have low albedo and trap heat and moisture.
Thus, loss of forest cover accentuated cooling and drying of climates, leading to further contraction of forests. By early Oligocene time South America and Australia had moved far enough away from Antarctica to allow water from the southern oceans to become trapped in a current around Antarctica, where they became very cold. As a result, glaciers grew on Antarctica. Mid-Oligocene eustatic fall in sea level result of expansion of Antarctic glaciers. Expansion of glaciers and lowering of sea level.