He was employed at Caltech's Division of Geological & Planetary Sciences at the time of writing the first edition.He is presently employed in the Space & Atmospheric Sciences Group at the Los Alamos National Laboratory. Wiens has a Ph D in Physics, with a minor in Geology.
Uranium-lead dating uses four different isotopes to find the age of the rock.
Because uranium is radioactive, it is constantly emitting particles and changing into other elements.
Uranium has a well-established radioactive decay series.
Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.
There are over forty such techniques, each using a different radioactive element or a different way of measuring them.