Science Forums 2

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Hyderogenbond - You stated: "Alien life would probably contain DNA since the laws of physics and chemistry should be the same everywhere." - Yes, and the size of the home planet should dictate the surface gravity and ocean pressures on the planet. - So as you suggested that an alien world that was hotter with the oxygen and ozone lower, may select for humanoids with reptile skin and sleeping in the day.

I don't know if this type of world could exist. If it were hotter, the oceans may evaporate on an earth-sized planet such as Venus. If on the other hand the alien planet was larger than earth the surface pressures would be greater, so smaller animals might evolve.

Again, these higher pressures would not allow brain expansion on these larger planets, and would be unlikely to develop advanced civilizations.

I suspect that if there are any advanced civilizations in our universe, there home planet is similar size to earth, either being a littler larger, or smaller, but not much difference.

The oceans would have sharks similar to ours with some of sea sloath evolution similar to human. - It might be a scary thought to think our earth is common to all like in the universe with jurassic worlds being the norm.