Astatine, Earth's Rarest Element
Astatine has never been directly observed, because if it was large enough to be visible, it would presumably vaporize from its own radioactivity. It was first produced in 1940 at the University of California Berkeley. In nature, it results from the decay of uranium and thorium. It is the artificially produced isotope astatine-211, however, that researchers hope might have applications in cancer treatment.
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Key Facts In This Video
Hydrogen makes up 90% of all atoms in the universe. (1:59)
An element's half-life is the amount of time that it takes for half of a given amount of that element to decay into something else. (6:12)
Scientists have only observed three atoms of Ununoctium so far. (10:22)