lkartchner Wrote:
Oct 16, 2012 9:49 PM
go for 3 Billion Years. 1.5 billion Years ago, the Earth went through a 5oo Million Year period of 'Snowball Earth' events. Each lasted approximately 50 million years. First, as CO2 levels fell, the Earth cooled, until even the tropics were under a mile of ice. After about 30 Million years of this, enough methane was released to raise the temperature until all the ice melted, even at the poles. over the next 20 Million Years, the methane and the resulting CO2 was broken down and taken out of the atmosphere by algae. We have examples throughout the geologic record of both higher and lower CO2 levels. There are also examples of both higher and lower temperatures. Over all that time, the only constant is that climate keeps changing.