Geologic Time
Scales
Precambrian
Paleozoic
Era
Cambrian
Period
Ordovician
Period
Silurian
Period
Devonian
Period
Carboniferous Period
Mesozoic
Era
Triassic
Period
Jurassic
Period
Cretaceous
Period
Cenozoic
Era
Tertiary
Period
Quaternary
Period
Geologic
Timeline
Web Sites
Precambrian.
UC Berkeley
Paleo
May Project. Indiana State University
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Kevin C. HartzogGeologic Time Scales
Precambrian
The Precambrian, dating 4.5-544 million years ago (mya), marks the period of Earth's history from its initial formation to the beginning of life. During this time range, our Earth went through vast changes. The Earth had solidified from the solar disk left over from the Sun's own formation. The Moon formed, setting the stage for later tidal fluctuations. As the Earth cooled, it developed its initial atmosphere that contained no oxygen, yet setting the stage for the development of the first life forms, prokaryotes. From their interaction with the then prevalently carbon dioxide and sulfur rich atmosphere, they slowly altered, developing into the first eukaryotes, and creating yet another profound change in Earth, the production of oxygen. As the atmosphere slowly became enriched in oxygen, complex multicellular organisms evolved, and the curtain had fallen upon one era of Earth's history, to arise in a new era, the Paleozoic. With one of the greatest events in life's theater on Earth, the Precambrian Explosion marked a moment when an abundance of fossils showed a vast increase in the numbers and diversity of life. Later shown to be a more gradual increase in Earth's diversity, this was still the most significant increase in life forms on our new, young planet.