The evolution of life
The first fossils
The oldest sedimentary rocks that we know of date back to 3 and a half billion years ago and they probably contain traces of life. These rocks were found in Canada, in South Africa and in Australia and have been given a precise age thanks to the radioisotope method. The chemical analysis of these rocks has revealed the presence of certain compounds that could be considered as “chemical fossils” because apparently they come exclusively from the metabolism of living beings. As a matter of fact we cannot be 100% certain about them being so ancient because the rocks may have been contaminated subsequently by organic material which was produced much more recently.
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