geological record
Quick Summary
The geological record is the history of Earth as documented in its rocks. This record is organized into a geologic time scale, which divides Earth's history into units like eons, eras, periods, and epochs.1
The primary method for establishing this scale has historically been stratigraphy, the study of rock layers, and the fossils found within them. The principle of superposition states that in undisturbed rock layers, the oldest are at the bottom and the youngest are at the top. Fossils are crucial because different species are characteristic of different time periods, allowing geologists to correlate rock strata globally.123
Modern geochronology uses radiometric dating to assign numerical ages to rocks, providing absolute dates in years. This has revealed that Earth is about 4.6 billion years old, with the Precambrian era comprising the vast majority of geologic time.23
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