I was reading the "Alien-Sky" thread and thought, "What would Earth be like if it orbited an Red-star and was the same distance and composition?
Well, one, it couldn't have formed at 1AU as that would have been in the ice-line and it had to be ejected there from closer in. Two it wouldn't be able to have CO2 in the atmosphere as it would freeze and snow; the same goes for liquid water. My guess is that as first, the Earth would be a molten-ball of lava etc. with a thick CO2 atmosphere; as time went on, it cooled off and the CO2 and water began to freeze creating a snow-ball Earth; now, would the Earth be able to hold onto its H and He? My guess that if you were to view an Earth like that orbiting a M-class Star 4 Billion years-old lie us, it would resemble a dirty snow ball with expanses of white broken by the continents exposing non-CO2 or H2O regions exposed by a much more active plate-tectonics system due to the extreme difference in temperature.