The geologic time scale is a record of the major events and diversity of life forms present in Earth's history. The geologic time scale began when Earth was formed and goes on until the present. It divides Earth's long history into units of time.
Precambrian
The Earliest Age of Earth's Geologic History
"Before the Cambrian Explosion"
Approximately 4.6 Billion Years Ago - 541 Million Years Ago
Includes Approximately 80%+ of Earths Entire History
Precambrian time extended from about 4.6 billion years ago (the point at which Earth began to form) to the beginning of the Cambrian Period, 541 million years ago. The Precambrian represents more than 80 percent of the total geologic record.
For billions of years, there was apparently no life on the planet. It wasn't until the end of Precambrian time that single-celled organisms appear to have came into existence. The end of this time span saw the rise of a few more complex animals in the oceans, such as organisms that resemble jellyfish. There was still no life on land, and the atmosphere was just beginning to accumulate the oxygen required for higher-order animals to even survive. Biodiversity really didn't increase until the first era of Earth's history.
Organisms found at the later end of Precambrian Time
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Catastrophic Events
- The Precambrian age is characterized by extensive volcanic eruptions and impact events including the formation of the Moon as the early Earth developed for billions of years.
- The Precambrian super-eon ended with the relatively rapid arrival or "explosion" of new organisms in the fossil record beginning the Paleozoic Era.
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Topic Tips
- The Precambrian "super-eon" includes most of Earth's history.
- A great deal of geologic events occurred during this time, but very little events in terms of biodiversity according to the fossil record compared to our current eon of Earth's history.