H2OThe pictures from Titan got me thinking, methane rivers and seas, could there be methane (CH4) based life? Life on earth is based on water, H2O. The thing that's special about water is not the two H's (the most abundant primordial element), it's the O. Oxygen is the lightest element that is highly reactive (it burns), but not too reactive like Flourine (it explodes). The two elements just below it, Nitrogen and Carbon, are stable to where they are the natural building blocks. So, chemistry as we know it on earth and as the base from which life evolves, is probably pretty much the same everywhere. On the next level up in the periodic table in the same slot as Oxygen is Sulphur -- which mostly binds w/ Oxygen (? 35 years since I've had chemistry), and probably does not have the cosmic abundance needed.