Question about early Earth

Was the Moon in a close Earth orbit essential in preventing a runaway greenhouse effect like we see on Venus. The Earth was much more volcanically active in it's youth and would have put out much more CO2 and other greenhouse gases. Did the Moon siphon off much of the Earth's atmosphere in earlier times.

I'm trying to figure what sort of planets we'll be looking for in the future that will be possible candidates for life outside our solar system. Obviously the gas giants we've found in close orbit around other stars couldn't support life. Would being in the right orbit around the right sized star be enough to create the conditions for terrestrial type life, or is a double planet like our Earth-Moon neccessary?