eons
Eons are the largest divisions of geologic time. In geology, an eon spans hundreds to billions of years and is subdivided into eras, periods, epochs, and ages. The term comes from the Greek aeon, meaning age or life.
Earth's geologic time recognizes four eons: Hadean, Archean, Proterozoic, and Phanerozoic.
The Hadean lasted roughly 4.6 to 4.0 billion years ago, when Earth formed and was largely molten.
The Archean, from about 4.0 to 2.5 billion years ago, saw crust formation and the earliest known
The Proterozoic, from 2.5 billion to about 541 million years ago, features rising atmospheric oxygen and the
The Phanerozoic, from about 541 million years ago to the present, includes most of the fossil record
Boundaries between eons are defined by the International Commission on Stratigraphy and correlate with significant changes
In practice, geologists use eons as the broad framework of the time scale; finer detail is provided