Not that weâd expect less after the cliffhanger last season. If you havenât yet watched the September 23rd premiere of Chicago Fire, and somehow have managed not to find out who died, donât keep reading. If you have, please join me in my misery.
The Precambrian Super-Eon lasted from the formation of Earth 4,567 million years ago until the start of the Pharerozoic Eon 542 million years ago. It lasted 4.025 billion years. 90% of Earth's history.
The great Precambrian expanse of time is divided into the Proterozoic, Archean, and Hadean eons in order of increasing age. The names of the eras in the Phanerozoic eon (the eon of visible life) are the Cenozoic (recent life), Mesozoic (middle life) and Paleozoic (ancient life). The further subdivision of the eras into 12 periods is based on identifiable but less profound changes in life-forms.