The geologic time scale is divided into eons, eras, periods ... The largest extinction events define a change in era. The end of the Paleozoic and beginning of the Mesozoic 251 million years ago marks ...

I like to use a meter stick and be very intentional with my spacing to model time as a scale. I also avoid using the far right of the space to infer ... preserved in the rock record of the Earth that ...

Prehistoric time line, geologic time scale, photos, facts ... in the foundational years of the Precambrian. The productive Paleozoic era gave rise to hard-shelled organisms, vertebrates ...