There are also Four Ages in J.R.R. Tolkien's mythos:

The First Age

Extending from the return of the Noldor to Middle-Earth to when Morgoth was cast out of Angband, it extended for 583 years. Most of the events in The Silmarillion take place in this age or The Elder Days.

The Second Age

Beginning with the foundation of Lindon and ending with the Defeat of Sauron, the most notable happening of this age is the rise and fall of Númenor. This age extended for 3441 years, and it's story is told in The Silmarillion in Akallabeth.

The Third Age

The Third Age began 4,024 years after the start of the First Age, and most of Lord of the Rings takes place in this age. It begins with the death of Isildur and ends with the departure of the Ring-bearers (except Sam) to Eressëa. The last chapter of The Silmarillion concerns the Third Age. This age lasts for 3021 years.

The Fourth Age

The Fourth Age begins with the departure of Frodo to Eressëa. During it, Sam, Legolas and Gimli set sail for Valinor and King Aragorn (Strider) dies. The last recorded event of this age is the completion of a copy of the Red Book (the "original" Westron version of Lord of the Rings) in Gondor.

Much more information can be found on the ages see the Chronicle of Arda (