Rarest element on Earth

Scientists have discovered that the radioactive transuranic element berkelium (discovered in December 1949, and given the symbol Bk and atomic number 97) can be produced naturally by neutron capture and beta-particle decay in highly concentrated Uranium deposits in the Earth's crust. Only a few atoms are made by this process each year. With a half-life of 330 days, estimates of the amount of berkelium within the Earth's crust at any one time are of the order of between 10 and 50 atoms, making it the rarest element naturally occuring on Earth. Previously held by the element astatine.