Below is the Geological Time Scale with radiometrically determined ages.  The next several pages will refer to various geological ages. Use this chart to determine how long ago those event occurred.

Quaternary 1.81 million years to present

Neogene 23.8 - 1.81 million years

Paleogene 65.5 -23.8 million years

Cretaceous 142 - 65.5 million years

Jurassic 205.1 - 142 million years

Triassic 250 - 205.1 million years

Permian 292 - 250 million years

Carboniferous 354 - 292 million years

Devonian 417 - 354 million years

Silurian 440 - 417 million years

Ordovician 495 - 440 million years

Cambrian 545 - 495 million years

The above periods are also grouped into Eras.  The Paleozoic era includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.  The Mesozoic era includes the Triassic, Jurassic, and Cretaceous.  The Cenozoic era includes the Paleogene, Neogene, and Quaternary.

The Paleogene and Neogene are further subdivided into epochs.  The epochs of the Paleogene are the Paleocene (65 - 55 million years ago), the Eocene (55 - 33.7 million years ago), and the Oligocene (33.7 - 23.8 million years ago).  The Neogene includes the Miocene (23.8 - 5.32 million years ago) and Pliocene (5.32 - 1.81 million years ago).