Palaeozoic

The Palaeozoic was an era of Earth history.

Horseshoe crabs were arthropods from the Palaeozoic. (PROSE: The Southwell Park Mermaid)

Martha Jones once thought about how "tomorrow" she could be sightseeing in the Palaeozoic Era. (PROSE: Wishing Well)

Behind the scenes
The Palaeozoic Era contained the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.