Models of the Sun's evolution predict the Sun was 70% percent as bright 2 billion years ago, and the Earth should have been an ice ball at that time. Yet the geological record indicates the oceans were liquid.
A number of explanations have been proposed which haven't faired well upon closer study. The lastest explanation says that the Earth at one time orbited closer to the Sun: http://www.sciencedaily.com/releases/2012/05/120530152034.htm Here is another: If LENR occurs inside the Earth then perhaps there was sufficient LENR activity in the Earth billions of years ago to keep the oceans liquid. harry
