* Named after prominent geographic features or regions where rocks from the era were first studied:

* Paleozoic: "ancient life," from Greek palaios ("old") and zoe ("life")

* Mesozoic: "middle life," from Greek mesos ("middle") and zoe ("life")

* Cenozoic: "recent life," from Greek kainos ("recent") and zoe ("life")

Periods:

* Usually named after geographic locations or geographic features where the rocks were first described or studied:

- Examples:

* Silurian: Named after the Silures tribe, who lived in what is now Wales and the Welsh Borderland.

* Devonian: Named after the county of Devon in England.

* Carboniferous: Named after the large amount of coal found in rocks from this period.