How are eras and periods of the geologic time scale named? •They are named for the places where geologists first described rocks or fossils from that time.
•Their names are based on the names of scientists who discovered the rocks and fossils.
•They are named after plants and animals that lived during that time.
•Their names are based on the number of centuries within that length of time.

They are named for the places where geologists first described rocks or fossils from that time.

Explanation:

The geological history of planet Earth is divided into multiple eras and periods. The divisions are based on some dramatic event that caused a significant change in a short period of time, thus creating an easy distinction between them. The purpose of the divisions is to be easier for the scientists to explore the past, to find it easier to describe fossils, rock strata, events, etc.

The names of the eras and periods of the geological time scale seem to be names that are familiar, at least to people in some regions, with slight changes at the end of the names. This is because the names of the eras and periods tend to be given by the places where geologists first described rocks or fossils from that time. As an example, we can take the Jurassic (named after the Jura Mountains), Devonian (named after the Devon), Cambrian (named after Cambria, which is the Latin name for Wales), etc.