Which German chemist discovered thorium's radioactivity two months before Marie Curie?

The German chemist who discovered thorium’s radioactivity two months before Marie Curie was Gerhard Carl Schmidt. In 1898, Schmidt investigated radiation from thorium compounds and reported that thorium emitted penetrating rays similar to those associated with uranium.

Marie Curie reached the same broad conclusion independently while systematically testing elements and minerals. Her paper on uranium and thorium radiation was presented to the French Academy of Sciences in April 1898, but Schmidt had already published his observation in Berlin roughly two months earlier. This makes Schmidt the prior discoverer in the specific historical race to identify thorium’s radioactivity.

The episode illustrates how rapidly scientists were pursuing the new radiation phenomenon after Becquerel’s 1896 discovery. Curie’s work nevertheless had a much wider impact: she introduced the term “radioactivity,” demonstrated that the property belonged to atoms, and used measurements of radioactive minerals to pursue the unknown elements polonium and radium.