1.What principles were used to develop the geologic time scale?

Question

1.What principles were used to develop the geologic time scale?

Answer 1

Geologic time scale is used to quickly classify events, rocks and fossils in the history of Earth.

Strata (and fossils  and rocks) for a specific period have specific characteristics: this forms a period.

On Mars, for instance,  the time scale of course would be very different.

For instance the end of the ice age was a major event ( a major event for humans anyway), and it is the beginning of the Holocene epoch.