What is the geologic time scale?

The geologic time scale is a standardized chronological framework used by Earth scientists to divide geological time into systematic intervals. It relies on the rock record, chronostratigraphic principles, and geochronological techniques like radiometric dating to establish the relative and absolute ages of rock sequences. International units and boundaries within this system are defined and maintained by the International Commission on Stratigraphy.

What we know

• The geologic time scale classifies geological strata in time using a system of chronological dating. [1]
• It places rock sequences into relative age positions by combining the rock record with principles of chronostratigraphy. [2]
• Geochronology techniques such as radiometric dating are used to precisely date boundaries between intervals on the time scale. [2]
• The International Commission on Stratigraphy is responsible for defining standardized international units of geological time. [2]

Where to go next

• how it workedHow do scientists determine the absolute ages of rock layers?
• how we knowWhich organizations oversee the official geologic time scale?
• a case in pointHow are individual sedimentary layers and beds formed?
• the bigger pictureWhat is stratigraphy?
• what caused itHow do Earth scientists use paleomagnetic properties in rock records?
• an unexpected connectionHow do fine layers in sedimentary rocks relate to vast geologic time intervals?Millimeter-scale sedimentary laminae provide microscopic physical evidence that helps researchers interpret the detailed sequence of events governed by the macro-level geologic time scale.

Sources

• [1]geologic time scale (Wikidata Q43521) · CC0 1.0
• [2]Geologic time scale · CC BY-SA 4.0
• [3]Glossary of geology · CC BY-SA 4.0
• [4]Bed (geology) · CC BY-SA 4.0
• [5]Lamination (geology) · CC BY-SA 4.0