qClimate in the past 500 million years have
alternated between long periods of warm climate and short periods of cold climate.
qDuring the last 500 million years, major
continent-size ice sheets existed on Earth during three
icehouse ear: (1) a brief interval near 430 Myr ago, (2) a much longer interval from 325
to 240 Myr ago, and (3) the current icehouse era of the last 35 million year.