If one knows how much of this radioactive material was present initially in the object (by determining how much of the material has decayed), and one knows the half-life of the material, one can deduce the age of the object.
Wiens has a Ph D in Physics, with a minor in Geology.
Further evidence comes from the complete agreement between radiometric dates and other dating methods such as counting tree rings or glacier ice core layers.
Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.His Ph D thesis was on isotope ratios in meteorites, including surface exposure dating.He was employed at Caltech's Division of Geological & Planetary Sciences at the time of writing the first edition.Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.