What is the rarest substance on earth?
the rarest substance on earth is possibly the element Astatine. It’s a highly unstable, radioactive halogen. It only exists for a very short period in the radioactive decay chains of Plutonium, Uranium and californium. It’s half life is very short, the most stable isotope has a half life of only 8.3 hours. At any one time it has been estimated that less than 28 grams (1 oz) exists anywhere on the earth. That’s less than you could fit in a teaspoon. Another possibility is Francium. about 30 grams of francium are estimated to exist on the earth at any time. we know very little about either of these elements. The isn’t enough around at any one time to really test their properties. Considering how radioactive they are that’s probably a good thing. The rarest isotope of any element must be Tantalum-180. It’s a very rare form of Tantalum and the only naturally occurring nuclear isomer an has a half life of only 8 hours.
