In turn, the extinction of the dinosaurs and several other animal groups 65.5 million years ago defines the beginning of the Cenozoic era. We are including several pages with geologic time scale data ...

The geological time scale, established by scientists in the mid-19th century and agreed upon internationally, breaks down the eternity of our planet's history into more manageable units than years.

I like to use a meter stick and be very intentional with my spacing to model time as a scale ... An Index fossil is any animal or plant preserved in the rock record of the Earth that is characteristic ...