Hard to imagine discovering and figuring out radioactivity from scratch. Hard to imagine too (on the other hand) that a hundred years ago it hadn't been done until Marie Curie went and did it. It's such a defining part of our modern world.

Dale Stromberg has a micro-fiction on what's arguably a reverse-Marie Curie theme. https://medium.com/@dale.stromberg/%C3%BEanne-ytemeste-fer%C3%BEyng-3efd51a12d28

Arturo Serrano has a chapter about the (fictionalized) early realizations about pitchblende in his alternate history novel, To Climates Unknown.