Here's a breakdown:

* Eon: The largest division of geological time.

* Era: A subdivision of an eon.

* Period: A subdivision of an era.

* Epoch: A subdivision of a period.

* Age: A subdivision of an epoch.

So, the order from largest to smallest is:

1. Eon

2. Era

3. Period

4. Epoch

5. Age

Let me know if you'd like more details on a specific era or its periods!