Hydrogen is the most common element in the universe. Here on Earth, it appears almost everywhere in some form or another. You can find it in the air, water, and in the Earths crust.
But what is the rarest element? That would be Astatine. Its a highly radioactive element with a half life of only 8 hours. Only trace amounts of Astatine have ever been found naturally. Most of the time, its only been observed in labs, as a by product of nuclear experimentation. But as radioactive as the element is, it disappears so quickly that it poses very little threat to humans.
On National Periodic Table Day, discover some of the strange and mysterious elements that form the world around us.