Radioisotope methods of dating
One early approach was based upon ocean salinity [John Joly, 1800's].
This assumed the ocean was initially pure water and that it's salinity was derived from continental erosion.
In other words, half of the radioactive isotope in a sample would have decayed to Nitrogen-14 (N-14) in just 5,730 years.
C-14 dating of carbon-bearing materials is therefore limited to roughly 50,000 years.
This implies the earth is at least 20 million years old.
This age is obtained from radiometric dating and is assumed by evolutionists to provide a sufficiently long time-frame for Darwinian evolution.
The time required for half the original number of parent atoms to decay is called the half life.
Some half-lives are listed below: It follows that uranium-lead, potassium-argon (K-Ar), and Rubidium-Strontium (Rb-Sr) decay can be used for very long time periods, whilst radiocarbon dating can only be used up to about 70,000 years. This uses a simple exponential decay formula linking the original number, Po, of parent atoms in rocks and minerals to the P atoms now present, thereby enabling an estimate of geological age.
In fact, organic samples from every portion of the Phanerozoic record (spanning the last 500 million years on OE dating) show detectable amounts of C-14.
The implication is that this organic material was either contaminated by new C-14, or it was buried much more recently and OE dating methods are suspect.