December 25, 2012 in Science
“The Precambrian (Pre-Cambrian) is the name which describes the large span of time in Earth’s history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale. It spans from the formation of Earth about 4570 Ma (million years) ago to the beginning of the Cambrian Period, about 542 Ma, when macroscopic hard-shelled animals first appeared in abundance.”
“Not much is known about the Precambrian, despite its making up roughly seven-eighths of the Earth’s history, and what little is known has largely been discovered in the past 50 years. The Precambrian fossil record is poor, and those fossils present (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.”
Hadean Era [Greek: underworld]
4.5 to 3.8 billion years ago = Io
Continents begin to form.
Archaean Era [Greek: beginning, origin]
3.8 to 2.5 billion years ago = Io/Europa/Ganymede/Callisto
A large percentage of the Earth’s continental crust formed. Simple oceanic organisms appear in fossil record.
Proterozoic Era [Greek: earlier life]
2.5 billion to 500 million years ago = Callisto/Titan/Triton/Mars
Atmospheric levels increase.
(Titan; natural color, near-infrared, infrared/natural)
Paleozoic Era [Greek: ancient life]
500 to 250 million years ago = New Earth
Atmosphere becomes breathable. Aquatic life rapidly evolves from simple to complex form.
Great Red Spot – 4.5
Io – 4
Europa – 3.5
Ganymede – 3
Callisto – 2.5
Titan – 2
Triton – 1.5
Earth – 0.5