The period of time from the end of the formation of the Earth as a separate planet to the beginning of written history, as recorded and illustrated by the succession of rocks: Geological time is the period of time that extends from the beginning of the world to the present day.

Geological time refers to an interval of time occupied by the Earth's geologic history, extending from about 3.9 billion years ago (corresponding to the age of the oldest known rocks) to the present day.

In other words, it is the part of the Earth's history that is recorded in rock strata.

The geological time scale is classified in intervals distinguished by characteristic geological and biological features as indicated by the following longest to the shortest durations, eon (one thousand million years), era (divided into several periods), period (unit of geological time during which a system of rocks is formed), and epoch (geologic time that is a subdivision of a period).

An arbitrary chronological arrangement of geological events: Normally a geological time scale is represented in the form of a chart, showing the names of various rock layers and indicating the estimated period of each geological unit of geological time.