Relative dating techniques, such as magnetic secular variation or stable isotope methods, offer the potential to improve this precision, but both methods suffer from problems that make broad application to many sites impossible.
The ratios of strontium-86 to rubidium and strontium-87 are thought to only be influenced by the radioactive decay of the rubidium-87 into strontium-87.
The number of protons in an atom determines which element it is, while the number of neutrons determines which isotope it is.
For example, strontium-86 has 38 protons and 48 neutrons, whereas strontium-87 has 38 protons and 49 neutrons.
Radioactive elements, such as rubidium-87 (but not strontium-86 or strontium-87), decay over time.
By evaluating the concentrations of all of these isotopes in a rock sample, scientists can determine what its original make-up of strontium and rubidium were.