Realative dating age of rocks
Most commonly, the event causes partial or total loss of the radiogenic daughter isotope, resulting in a reduced age.
The first is to search for and date the oldest rocks exposed on the surface of the Earth.
These oldest rocks are metamorphic rocks with earlier but now erased histories, so the ages obtained in this way are minimum ages for the Earth.
Because the Earth formed as part of the Solar System, a second approach is to date extraterrestrial objects, i.e., meteorites and samples from the Moon.
The best evidence is contained in the Earth’s incomplete and complex but accurate stratigraphic record — a record that has been the subject of nearly two centuries of study.
Slowly and painstakingly, geologists have assembled this record into the generalized geologic time scale shown in Figure 1.