chronometric time scale

The geologic time scale is a system used to describe the history of Earth, dividing it into named units of time such as eons, eras, periods, and epochs. This scale is primarily based on the study of rock strata and the fossil record. The emergence and disappearance of species throughout Earth's history, as seen in fossils, help define the boundaries of these time intervals.12

Geochronology is the field dedicated to determining the age of Earth's rocks and deciphering its geologic history. Initially, relative ages were determined by the position of rock layers (superposition) and their fossil content. The development of radiometric dating methods, which measure the decay rates of radioactive elements in rocks, has allowed for the numerical quantification of geologic time, providing absolute ages for these historical intervals. This has been crucial for understanding the vast span of Earth's history, especially the Precambrian era, which predates most fossil evidence.23