Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures.

Biological activity is a major factor in Earth's chemical cycles, including facilitating CO sequestration and providing climate feedbacks. Thus a key question in Earth's evolution is when did life arise and impact hydrosphere-atmosphere-lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800-3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals from the Isua supracrustal belt (ISB), southwest Greenland. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1-4-cm-high stromatolites-macroscopically layered structures produced by microbial communities.

Earth's oldest mantle fabrics indicate Eoarchaean subduction.

The extension of subduction processes into the Eoarchaean era (4.0-3.6 Ga) is controversial.

Comment on "A vestige of Earth's oldest ophiolite".

Furnes et al. (Reports, 23 March 2007, p. 1704) reported the identification of an ophiolite sequence within the approximately 3.