OK it’s a bit late to enter this thread, but it is a very intriguing topic: how important is the moon for life?

Simon Conway Morris' book “Life’s Solution: Inevitable Humans in a Lonely Universe” argues (roughly) that on any Earth-like planet evolution would follow approximately the same course -always assuming no totally catastrophic event- because evolution is highly convergent, however, because the solar system, and the Earth in particular is rather unusual, life as we know it may be very rare indeed. Effectively it is a rebuttal of the Catastrophic Contingency model of evolution that was popularized by S Gould. In the chapter “Uniquely Lucky? The Strangeness of Earth” he discusses the importance of the moon. Quoting from an article by AGW Cameron and W. Benz (Icarus, 92; 204, 1991) he says: -

“We deal with a unique event. In the absence of the Giant Impact, it seems plausible that the Earth would have developed with a massive atmosphere comparable to that possessed by Venus. Just as in the case of Venus, it seems unlikely that life would have developed in such an environment.”

Other moon-related hypotheses he raises in this chapter are whether without a moon, the change in stability of the axis would have caused massive weather fluctuations that would suppress life; would increased wind speeds on a moonless Earth have an effect on evolution (e.g. of flight, of stature etc.), the possibility that without a moon-forming collision the size of the planet might had been different and it might consequently be either a water-world or very arid. I liked the idea of the importance of tide pools that was raised earlier in this thread; whatever role they played in initiating life, the tide pools probably acted as an important interface in the later transition from the water to dry land.

I tend to disagree with Morris overall, however, simply because I think that the basic mantra of evolution is “shit happens, deal with it”. Life –once underway- is robust and apart from utter cataclysms or total deprivation of resources (e.g. water, nutrients) is difficult to destroy.

Andrew