Primordial matter consist of primordial nuclides. Primordial nuclides are nuclides found on the Earth that had 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 that occurred before the solar system’s formation. Only 288 such nuclides are known.
Bismuth, thorium, uranium and plutonium are primordial nuclides because they have half-lives long enough to still be found on the Earth, while all the others are produced either by radioactive decay or are synthesized in laboratories and nuclear reactors.
