The accepted divisions of geologic time are the Precambrian era [which spans the billions of years before complex lifeforms appeared], the Paleozoic [which is defined by evolving lifeforms[, the Mesozoic [which begins with an event that caused utter devastion of life] and the contemporary Cenozoic era [marked by another mass extinction of life, and the evolution of humanity].
Geologic Time is divided into Supereons(such as Pre-Cambrian), which are divided into Eons(Phanerozoic), then Eras(Cenozoic), then Periods(Quaternary), then Epochs(Holocene), and finally Ages(Dark Age).
Standard divisions in chronological order (oldest to youngest) are precambrian, cambrian, ordovician, silurian, devonian, mississippian, pennsylvanian, permian, triassic, jurassic, cretaceous, tertiary, quarternary.
The history of the earth is divided into two eons. Phanerozoic - showing signs of visible life and Cryptozoic - when the Earth was formed showing no evidence of life.
The Precambrian, the Paleozoic Era (which is the age of ancient life), the Mesozoic Era (which is the age of medieval life) and finally the Cenozoic Era (which is the age of recent life).
