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.
Moreover, many of the oldest dated rocks intrude still older but undatable rocks.
There can be no doubt about the Earth’s antiquity; the evidence is abundant, conclusive, and readily available to all who care to examine it.The last modification to the geologic time scale of Figure 1 was in the 1930s, before radiometric dating was fully developed, when the Oligocene Epoch was inserted between the Eocene and the Miocene.Although early stratigraphers could determine the relative order of rock units and fossils, they could only estimate the lengths of time involved by observing the rates of present geologic processes and comparing the rocks produced by those processes with those preserved in the stratigraphic record.With the development of modern radiometric dating methods in the late 1940s and 1950s, it was possible for the first time not only to measure the lengths of the eras, periods, and epochs but also to check the relative order of these geologic time units.Radiometric dating verified that the relative time scale determined by stratigraphers and paleontologists (Figure 1) is absolutely correct, a result that could only have been obtained if both the relative time scale and radiometric dating methods were correct.Literally many tens of thousands of radiometric age measurements are documented in the scientific literature.