Pre-Cambrian
Pre-Cambrian is an informal term in geology and paleontology for the time from the formation of the Earth about 4500 million years ago to the Cambrian explosion of life that occurred 542 mya, which marked the beginning of the Paleozoic Era and the Cambrian Period. Little is known about the Pre-Cambrian, despite the fact that it constitutes the vast majority of our planet's history.
The Pre-Cambrian saw the origin of life, the evolution of photosynthesis, the transformation of Earth's atmosphere into its modern form, and the creation of iron ore.
In non-scientific writing, the Pre-Cambrian is often imprecisely referred to as a "period" or "era", but "period" and "era" are technical terms of geology, and the Pre-Cambrian is itself made up of several periods (such as the Ediacaran) and eras (namely, the Hadean, Archaean, and Phanerozoic).
| A brief history of Geologic time |
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Pre-Cambrian - Cambrian - Ordovician - Silurian - Devonian - Carboniferous - Permian - Triassic - Jurassic - Cretaceous - Paleogene - Neogene - Quaternary |