He also formulated the law of superposition, which states that any given stratum is probably older than those above it and younger than those below it.
While Steno's principles were simple, applying them proved challenging.
Corresponding to eons, eras, periods, epochs and ages, the terms "eonothem", "erathem", "system", "series", "stage" are used to refer to the layers of rock that belong to these stretches of geologic time in Earth's history.
For example, in North America, the Lower Cambrian is called the Waucoban series that is then subdivided into zones based on succession of trilobites.
The first three of these can be referred to collectively as the Precambrian supereon.
Eons are divided into eras, which are in turn divided into periods, epochs and ages.
The following four timelines show the geologic time scale.
The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon.
In the late 17th century Nicholas Steno (1638–1686) pronounced the principles underlying geologic (geological) time scales.