The rarest element on Earth is Astatine, a radioactive element with the atomic number 85 on the periodic table. It’s so unstable that its most stable isotope, Astatine-210, has a half-life of only 8.1 hours. This means that any Astatine that is produced quickly decays.
Astatine is produced by the decay of heavier elements, and at any given moment, it’s estimated that there is less than an ounce (around 28 grams) of Astatine in the Earth’s crust.
Because of its extreme rarity and radioactivity, Astatine has no commercial applications and is of interest only for research purposes. It’s primarily produced in the laboratory by bombarding bismuth with alpha particles.