Geological time scale

The geological time scale is a framework used by geologists, paleontologists, and other scientists to divide Earth's history into distinct intervals based on significant events, changes in the environment, and the evolution of life forms. It provides a chronological timeline that spans billions of years, organizing Earth's history into smaller, manageable units. 

The largest subdivisions of geological time are known as eons, which represent the longest intervals of time in Earth's history. Currently, Earth's history is divided into four eons: the Hadean, Archean, Proterozoic, and Phanerozoic eons.

Eons are further divided into eras, which represent significant periods characterized by distinctive geological and biological events. The Phanerozoic eon, the most recent eon, is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic eras.

Each era is subdivided into periods, which represent shorter intervals of time marked by specific geological and biological developments. For example, the Paleozoic era is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

Periods are further divided into epochs, which represent even smaller units of time characterized by more localized geological and biological events. Epochs provide finer-scale resolution within periods and are often based on specific changes in Earth's climate, sea levels, or faunal assemblages.

Ages and Chronostratigraphic Units:
The smallest subdivisions of the geological time scale are ages and chronostratigraphic units, which represent the shortest intervals of time and are typically defined by specific geological events or fossil assemblages. Ages are often named after distinctive rock formations or geographic locations where they were first identified.

Boundaries and Correlation:
Boundaries between divisions of the geological time scale are defined by significant geological or biological events, such as mass extinctions, major shifts in Earth's climate, or the appearance of key fossil taxa. These boundaries serve as reference points for correlating rocks and fossils across different regions of the world.


Geological time scale