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[QUOTE]Originally posted by The Shadow: [QB] It doesn't really take into account the apparent size of the universe, which is either really, really big, or infinite. So unlikely stuff could still happen somewhere, but far enough away that I'm still not going to run SETI@home. [IMG]http://flare.solareclipse.net/smile.gif[/IMG] A few things, though: "Our solar system is the perfect distance, 25,000 light-years, from the centre of the Milky Way. Any closer, and we would have been clobbered by exploding stars or zapped by radiation from a black hole by now. Too far out, and there wouldn't be enough metal-creating stars to have formed the planet in the first place." The part about the metal sounds right, but you'd have to get closer to the center of the galaxy for frequent problems with radiation and black holes. "We're extremely fortunate in having Jupiter in the neighbourhood. Its gravity acts as a shield, sweeping up 99 per cent of the cosmic debris that could otherwise collide with Earth and destroy life (the asteroid it did let through 65 million years ago extinguished the dinosaurs)." It's probably let quite a bit through, actually, since it's big, but not that big...it's orbit will still leave plenty of room for lots of stuff to get close to the earth. Besides, since gas giants form commonly, the likelihood of getting a planet similar to Jupiter isn't that low. "And as the third planet in, we're perfectly positioned: Earth neither boils like Venus nor freezes like Mars." Isn't Mercury really cold, though? The orbit and rotation of planets has a lot to do with the surface temperature too. "Our moon is relatively large for a planet this size...there is now evidence that it was formed by an impact on the young Earth - yet another happy ``accident'' in the planet's history." Of course, moon-sized planets that come near earth-sized planets have a chance of being caught in each others' gravity anyway, although that's also not especially likely. More likely is two smaller moons of an earth-sized planet crashing into each other to create a larger one. We can also hope that some of those way-distant intelligent life forms had the courtesy to travel the universe and terraform/build some planets, but that's hoping for a bit much. [/QB][/QUOTE]
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