Here's the geologic time scale in order from longest to shortest:

* Eon: The largest unit of geologic time. Examples include the Phanerozoic Eon (current eon) and the Precambrian Eon.

* Era: A subdivision of an eon. Examples include the Paleozoic Era, Mesozoic Era, and Cenozoic Era (all within the Phanerozoic Eon).

* Period: A subdivision of an era. Examples include the Triassic Period, Jurassic Period, and Cretaceous Period (all within the Mesozoic Era).

* Epoch: A subdivision of a period. Examples include the Paleocene Epoch, Eocene Epoch, and Oligocene Epoch (all within the Paleogene Period of the Cenozoic Era).

* Age: The smallest unit of geologic time, representing a distinct interval within an epoch.

Think of it like this:

* Eon: The "Chapter"

* Era: The "Section"

* Period: The "Chapter Subheading"

* Epoch: The "Paragraph"

* Age: The "Sentence"