With land bridges connecting Africa to Eurasia, and North America to South America, ocean currents which served to circulate heat properly to keep the planet's temperature uniform were shut down. This led to greater extremes in temperature between the polar regions and the equatorial regions. Also, with Antarctica occupying the place it does, it acts as a perfect accumulation place for snow and ice, and is insulated from the warm oceanic currents by the cold circum-Antarctic south polar current. The net result of this poor heat circulation and Antarctic icecube is the overall cooling of the Earth's climate. This causes what are know as "Ice Ages". We are currently living in an Ice Age, which can loosely be defined as a time when icesheets exist at one or both poles on a year-round basis.
