Primordial radionuclide
Primordial radionuclides existed before the earth was created. They were present in the interstellar dust from which the solar system evolved, and were formed by nucleosynthesis in supernovae. Because the age of the earth is 4.58×109 y, the half-life of primordial nuclides must be greater than about 108 y. The name is derived from the Latin word primordium, meaning "origin".The following Table shows some examples of primordial radionuclides. See also natural decay chains.
| nuclide | T½ (year) | abundance (atomic%) |
|---|---|---|
| 40K | 1.29×109 | 0.0118 |
| 87Rb | 4.7×1010 | 27.8 |
| 115In | 6×1014 | 95.7 |
| 123Te | 1.24×1013 | 0.87 |
| 138La | 1.3×1011 | 0.09 |
| 144Nd | 2.1×1015 | 23.9 |
| 147Sm | 1.06×1011 | 15.0 |
| 148Sm | 7×1015 | 11.2 |
| 152Gd | 1.1×1011 | 0.2 |
| 174Hf | 2.0×1014 | 0.18 |
| 186Os | 2×1015 | 1.6 |
| 190Pt | 6.1×1011 | 0.013 |
| 204Pb | 1.2×1017 | 1.4 |