Marie Curie made many discoveries that contribute to the data we have today. Curie discovered Uranium rays caused the air around the sample to conduct electricity. She discovered the activity of the Uranium compounds depended only on the quantity of Uranium Present. In 1898 she discovered Thorium was also radioactive. Another discovery she made in 1898 is Polonium , Curie and her husband also discovered Radium (coined the word radioactivity). One of my favorite discoveries she made is that her electrometer showed that Pitchblende was four times as active as Uranium and Chalcolite two times more active. These two minerals contain small quantities of substance far more active than Uranium. Do you know what this means ? This means that there is still a chance that anything could happen! (radioactive wise).