This is HUGE news. I'm amazed that the press is being so nonchalant about it. Well, the NASA press release had a few multisyllable words. That's too hard to read for most members of the press (Joe B excepted).
This does raise all the questions you mentioned Seth. But there's one interesting question that I don't believe I've heard the exobiologists bring up. I'll express it in a roundabout way. It's clear that the more we learn about Earth, the more places we find life. Extremophiles live in hot, acidic water. They live in cracks deep in the mantle of the earth. They live frozen in ice and high in the atmosphere. This knowledge has certainly caused us to broaden our sense of possibility about the origin of life. There may be conditions on Mars now that are close to conditions where things are alive here. But what we don't really know yet is whether life on Earth originated under all these conditions. It may have. Or it may have originated in more traditionally "favorable" conditions and then radiated outward into these extreme niches. One might certainly imagine that, once life had a foothold, evolution could eventually find forms that could survive in extreme conditions--conditions where the chemistry might not have kicked off life ex nihilo. I guess we won't know till we know. MC