In
geochemistry and geo
nuclear physics,
primordial nuclides, also known as
primordial isotopes, are
nuclides found on the
Earth that have existed in their current form since before
Earth was formed. Primordial nuclides are residues from the
Big Bang, from
cosmogenic sources, and from ancient
supernova explosions which occurred before the formation of the
Solar System. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet
accretion until the present. Only 288 such nuclides are known.