Climate Changes in the Last 500 Myr
			q Climate in the past 500 million years have alternated between long periods of warm climate and short periods of cold climate. q During 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.