Pierre and Marie Curie, French scientists, with their daughter Irene, 1904.

Pierre and Marie Curie, French scientists, with their daughter Irene, 1904. Polish-born Marie Curie (1867-1934) and her husband Pierre (1859-1906) continued the work on radioactivity started by Henri Becquerel. In 1898, they discovered two new elements, polonium and radium. Marie did most of the work of producing these elements, and to this day her notebooks are still too radioactive to use. She went on to become the first woman to be awarded a doctorate in France, and continued her work after Pierre's death in 1906. In 1903 they shared the Nobel Prize for Physics with Becquerel. Irene also became a scientist, winning the Nobel Prize for Chemistry in 1935 for the discovery of artificial radioactivity. (Photo by Oxford Science Archive/Print Collector/Getty Images)