Here's a breakdown:
Eon: The largest unit of geological time. There are four eons: Hadean, Archean, Proterozoic, and Phanerozoic.
Era: Within each eon, there are eras. For example, the Phanerozoic eon is divided into the Paleozoic, Mesozoic, and Cenozoic eras.
Period: Each era is further divided into periods. For example, the Mesozoic era has the Triassic, Jurassic, and Cretaceous periods.
Epoch: Periods are further subdivided into epochs. For example, the Paleogene period of the Cenozoic era has the Paleocene, Eocene, Oligocene, and Miocene epochs.
Example:
* Eon: Phanerozoic
* Era: Mesozoic
* Period: Jurassic
* Epoch: (There are no epochs defined for the Jurassic period, but other periods do have epochs)
This hierarchical system provides a more detailed way to study the geological history of Earth.
