Older time spans, which predate the reliable fossil record (before the Proterozoic Eon), are defined by their absolute age.
Some other planets and moons within the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars and the Earth's Moon.
Whatever the case, the ICS has not officially approved the term, as of September 2015.
In Ancient Greece, Aristotle (384-322 BCE) observed that fossils of seashells in rocks resembled seashells found on beaches - he inferred that the fossils had once formed part of living animals, and he reasoned that the positions of land and sea had changed over long periods of time.
The geological time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth’s history.
The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy.
Leonardo da Vinci (1452-1519) concurred with Aristotle's interpretation that fossils represented the remains of ancient life.