Primordial elements are chemical elements found on the earth that have existed in their current form since before the earth was formed, according to the big bang theory. This means that the half-life on the given atoms must be greater than about 4.5×10⁹ years. The mass of the atom is also very important. Heavier atoms would need longer half lives to be primordial because lighter elements are formed more often in stellar reactions.

Hydrogen, helium (both helium-3 and helium-4), most deuterium, and some lithium-7 are examples of primordial elements, but tritium is not. All stable isotopes are primordial, as are some radioactive isotopes including thorium-232, uranium-235, uranium-238, potassium-40, and rubidium-87. It has also been shown that plutonium-244 is a primordial isotope, although just barely as its concentration in ores is nearly undetectable.

See also

• Classical element
• Origin of life
• Primordial sea