Earth Science

Earth History

Geological Time Scale

Study Tip
To remember the organization of the geologic time scale, use this mnemonic device: Every Elephant Plays Energetically (Eon Era Period Epoch)
Study Tip
To remember the organization of the geologic time scale, use this mnemonic device: Every Elephant Plays Energetically (Eon Era Period Epoch)

Main Idea

Scientists created the geologic time scale based on fossil evidence. It divides Earth’s history into blocks of time with each block separated by important events, such as the disappearance of a species of fossil from the rock record.

Organization

In the geologic time scale, the youngest ages are on the top and the oldest on the bottom.

The time scale is based upon relative times, therefore there aren’t any specific times listed with each era. The timescale is divided into eons, each eon into eras, each era into periods, and each period into epochs.

Concept Check
  • What evidence was used to build the geologic time scale?
  • What is the difference between relative time and absolute time?
  • How is the geologic time scale divided?