the Conservatives made Venus uninhabitable (too much global warming, too hot now) before they died off on that planet. That's a bad prospect for Earth.
Or could if have to do with the distance to the sun?
Methane isn't especially associated with living things. It's a not uncommon product to form if you have a lot of C and a lot of H and not enough O(xygen) to make carbohydrates. On earth, O is associated with live.