| Astatine is the rarest naturally-occurring element, with the total amount in Earth's crust estimated to be less than 1 oz
(28 g) at any given time; this amounts to less than one teaspoon of the element. The Guinness Book of Records has dubbed the
element the rarest on Earth, stating: "Only around 25g of the element astatine (At) occurring naturally"; Isaac Asimov, in
a 1955 essay on large numbers, scientific notation, and the size of the atom, wrote that in "all of North and South America to a depth of ten miles", the number of astatine atoms at any time was "only
a trillion".
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Natural Occurence