Therefore, the second timeline shows an expanded view of the most recent eon.
In a similar way, the most recent era is expanded in the third timeline, and the most recent period is expanded in the fourth timeline.
In the late 17th century Nicholas Steno (1638–1686) pronounced the principles underlying geologic (geological) time scales.
Steno argued that rock layers (or strata) were laid down in succession, and that each represents a "slice" of time.
For example, the lower Jurassic Series in chronostratigraphy corresponds to the early Jurassic Epoch in geochronology.
The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic." Evidence from radiometric dating indicates that Earth is about 4.54 billion years old.
It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.
Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon.
The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.
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.