Well, yes, science certainly advances and 'evolves', but I would strongly disagree with that characterization of it...
Most theories today will be just as good a hundred years from now, and for as long as humans are still around and doing science. Remember, what a theory is is a model which attempts to explain some phenomena for the purpose of having predictive power over it. New observations and insights via improved technology may change the model, but whatever it changes to must explain and be consistent with the old observations as well as the new. Hence the new theory must still contain the essence of the old one. E.g. Newton's model of gravity treats it as a force obeying the inverse square law. Einstein replaced this with a geometric interpretation which is shown to be more correct. Is Newton's theory wrong? No. His model is imperfect, as all models are, but the theory is still just as useful as it ever was, and Einstein's reduces to it when you take the appropriate limits. And we know Einstein's model isn't fully correct either, and suspect it will be replaced by some quantum mechanical model which will allow us to explore even broader conditions.
The alternative, which can and does happen, is that a theory or something close to it is found to be completely wrong. This usually happens when we missed something very profound, either by sheer stubbornness or lack of adequate observations (e.g. steady state model, aether, spontaneous generation). Similarly, new ideas are often rejected at first even when they are later shown to be correct. (E.g. white dwarfs and black holes, initially thought way too crazy to be real entities.) But these are the exception, not the rule. Science isn't much like trying to build a house, demolishing it, and building it again. It's more like building a house while constantly checking and throwing out the bad materials. And sometimes you do need a renovation, but you usually don't destroy the whole room. You clean and then add to it.
Anyway, methane on Mars -- this is super cool. We'd of course seen these before from orbit, but characterizing the source was very difficult as the emissions covered a large area and didn't stick around long. I'd never have guessed that (apparently?) they are this highly localized. Whether biological or geological (obviously hoping for the former), it should prove to be very interesting.
