Hadean

The Hadean is a geologic period; a somewhat outdated term for the time period prior to 3,800,000,000 years before the present -- 3800MA. It was originally intended to address the period before the earliest known rocks. In the last decades of the 20th Century a few Hadean rocks have been identified in Western Greenland, Northwestern Canada and West Australia. The term is not often used.

The oldest known rock formations are somewhat altered sediments from Greenland dated around 3800MA by a volcanic dike that penetrated the rocks after they were deposited. Individual zircon crystals redeposited in sediments in Western Canada and the Jack Hills region of West Australia are much older. The oldest dated zircons date from about 4400MA which is very close to the hypothesized time of the Earth's formation. The Greenland sediments include Banded Iron beds. They contain possibly organic carbon and quite possibly indicate that photosynthetic life was already in place at that time. The oldest known fossils (from Australia) are a few hundred million years younger.

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