The smallest division of geological time scale is

The smallest division of the geological time scale is a stage. A stage is a subdivision of a period, which is a subdivision of an era, which is a subdivision of an eon. The geological time scale is a system of chronological classification that divides Earth history into eons, eras, periods, epochs, and stages. The system is based on the principle of superposition, in which older layers of rock are always found below younger layers. The geological time scale is used to correlate rock units and fossils from different parts of the world.

• Eon: The largest division of the geological time scale, an eon is a unit of geological time that is longer than an era. The Phanerozoic eon, for example, began 541 million years ago and continues to the present day.
• Era: A division of the geological time scale that is longer than a period but shorter than an eon. The Phanerozoic eon, for example, is divided into the Paleozoic, Mesozoic, and Cenozoic eras.
• Period: A division of the geological time scale that is longer than an epoch but shorter than an era. The Phanerozoic eon, for example, is divided into the Paleozoic, Mesozoic, and Cenozoic periods.
• Epoch: A division of the geological time scale that is longer than a stage but shorter than a period. The Cenozoic era, for example, is divided into the Paleogene, Neogene, and Quaternary epochs.
• Stage: The smallest division of the geological time scale, a stage is a subdivision of a period. The Cenozoic era, for example, is divided into the Paleogene, Neogene, and Quaternary periods, which are further subdivided into stages.