When was radon first identified as a distinct element?

Radon was first recognized around the turn of the 20th century, with major work by Friedrich Ernst Dorn in 1900. Dorn identified a radioactive gas produced by radium, which he called radium emanation. Later research showed that this gas was a new noble gas, now known as radon. Because radon is radioactive and naturally produced from the decay of uranium in rocks and soil, it is important in environmental and health science.