Here's a breakdown of the geological time scale from largest to smallest:
* Eon: The largest division of geologic time, representing hundreds of millions to billions of years. (e.g., Phanerozoic Eon)
* Era: A subdivision of an eon, typically lasting tens to hundreds of millions of years. (e.g., Mesozoic Era)
* Period: A subdivision of an era, lasting tens to hundreds of millions of years. (e.g., Cretaceous Period)
* Epoch: A subdivision of a period, lasting millions to tens of millions of years. (e.g., Paleocene Epoch)
* Age: A subdivision of an epoch, but not always formally defined or used.
While the age is smaller than an epoch, it's not consistently used as a formal unit of geologic time like the others.
