I've been reading about the work of Marie Curie recently after a friend filled me in on what she did (never having had much of an idea previously) and it's all very interesting.

What I can't understand however is what real impact her discovery of radium had for the development of physics in general? I mean in the textbooks and websites I've been browsing, Curie is made out to be some sort of physics pioneer - but I can't see where her discoveries specifically moved the study of physics forward (don't get me wrong, I'm sure she was extremely influential, I'm just trying to understand **why**).

How did the discovery of radium/radioactivity impact the study of physics? What impact did Marie Curie have in actually moving towards modern physics? I can only seem to find a variety of claims that she did impact physics, rather than how specifically - it all seems a bit odd.