Geologic Time is a crucial concept to understanding the history of the earth—including the evolution ... The geologic time scale is divided into eons, eras, periods, epochs, and ages. Our activities, ...

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.

The Precambrian eon is vast ... The Precambrian encompasses 86 percent of the history of Earth. As its name implies, this includes all of geological time prior to the Cambrian period.