quote:
Mike Doran: Couple of background points. According to Carl Sagan's essay on an ever lumenous sun, if you are speaking of larger timescales--on order of billions of years, the sun was LESS lumenous than it is now when early life first came into being. About 25 percent less 4 billion years ago. Therefore, it is reasonable to assume that the planet was cooler and drier as an initial state. That would be good for nucleotides, which would do better under these conditions.
/*DNAunion*/ The majority picture has the Earth being hotter 4 billion years ago, or abouts. The sun would not have been the major contributor to surface temperatures here on Earth. The Earth formed by coalescing and those huge impacts generated enormous heat (enough to turn the "pre-Earth" into a molten ball of rock, which the heavier elements then sank down into the center due to their greater density), and the late heavy bombardment is thought to have ended only about 3.8 or 3.9 billion years ago (so the Earth was hot even up to then). Also, the Earth 4 billion years ago, or there abouts, is also thought to have been very active volcano-wise, which is why many scientists now believe the prebiotic atmosphere contained a lot of carbon dioxide (and other volcanic exhalations).
[This message has been edited by DNAunion, 11-05-2003]
™ Version 4.2