How Earth Escaped Mars' Cold Fate

This article talks about how Earth suceeded in staying unfrozen while Mars did not early in both planets' histories. Scientists found a group of very old rocks on Earth, and their composition indicates that there was a high amount of carbon dioxide in the atmosphere in Earth's early past. While it appears to be a bane of modern existence, carbon dioixde, and the greenhouse effect, seem to have kept Earth warm enough for water to flow back then when the sun was younger and much cooler. Mars was not so lucky (or maybe it was and something happened, we don't know), and lost its greenhouse effect before the sun warmed enough to keep the planet going on its own. Since Mars is farther away from the sun, the sun may not have ever been able to keep the planet warm, but the article doesn't talk about that. It focuses on the fact that we now have pretty good proof that Earth was once a sphere warmed by the greehouse process, and that enabled the planet to progress and live while Mars died.