The most astounding advance to emerge from the 19th C was the Darwinin Wallace theory of Organic Evolution.
The most powerful idea to emerge from the 20th was the concept of physical evolution - that the elements are transformed through nucleosynthesis and we are composed of billion year old carbon.
I understood the seminal paper was written in the late 1950's, by Burbidge, Burbidge, Hoyle, Fowler which defined the mechanism by which stars produce the heavy elements.
Another contributor to the science of this gradual realisation of physical evolution was Hans Bethe (1906—2005)
http://skyandtelescope.com/news/article_1475_1.asp