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Oldest evidence for complex life in doubt

Chemical fossils may have migrated into rock after sediments formed

Chemical biomarkers in ancient Australian rocks, once thought to be the oldest known evidence of complex life on Earth, may have infiltrated long after the sediments were laid down, new analyses suggest.

The evidence was based on biomarkers — distinctive chemical compounds produced today by modern-day relatives of cyanobacteria and other complex life forms. In 1999, a team of researchers contended that the biomarkers in the 2.7-billion–year-old rocks pushed back the origins of cyanobacteria by at least 550 million years and of eukaryotes by about a billion years.

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