Until recently we didn't even think natural thorium isotopes were radioactive, since the half life is close to the age of the universe. Huh? Thorium was the 2n

Until recently we didn't even think natural thorium isotopes were radioactive, since the half life is close to the age of the universe. Huh? Thorium was the 2nd element Marie Curie discovered to be radioactive, in 1898 according to wikipedia [0]. In fact the whole thorium decay chain [1] was classified even before anyone could identify what elements they were, resulting in the historic names "mesothorium", "radiothorium", etc [1]. Were you thinking of bismuth? [2] [0] https://en.wikipedia.org/wiki/Marie_Curie#New_elements https://en.wikipedia.org/wiki/Marie_Curie#New_elements [1] https://en.wikipedia.org/wiki/Decay_chain#Thorium_series https://en.wikipedia.org/wiki/Decay_chain#Thorium_series [2] https://en.wikipedia.org/wiki/Bismuth-209 https://en.wikipedia.org/wiki/Bismuth-209