Most commonly, the event causes partial or total loss of the radiogenic daughter isotope, resulting in a reduced age.
Not all metamorphisms completely erase the radiometric record of a rock’s age, although many do.
Many of these samples have not had so intense nor so complex histories as the oldest Earth rocks, and they commonly record events nearer or equal to the time of formation of the planets.
The third approach, and the one that scientists think gives the most accurate age for the Earth, the other planets, and the Solar System, is to determine model lead ages for the Earth, the Moon, and meteorites.
Thus, the radiometric ages obtained from these oldest rocks are not necessarily the age of the first event in the history of the rock.