Literally many tens of thousands of radiometric age measurements are documented in the scientific literature.Since beginning operation in the early 1960s, the Geochronology laboratories of the U. Geological Survey in Menlo Park, California, have C ages.All the major continents contain a core of very old rocks fringed by younger rocks.
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.
Present evidence indicates, however, that these intervals were rather short (100-200 million years) in comparison with the length of time that has elapsed since the Solar System formed some 4 to 5 billion years ago.
Thus, the ages of the Earth, the Moon, and meteorites as measured by different methods represent slightly different events, although the differences in these ages are generally slight, and so, for the purposes of this chapter they are here treated as a single event.
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.
Three basic approaches are used to determine the age of the Earth.