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Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures
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Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures
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Journal Article
Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures
2016
Overview
Stromatolite fossils formed around 3,700 million years ago in what is now Greenland predate the previous oldest fossil evidence for life on Earth by more than 200 million years.
Signs of life on an ancient Earth
Stromatolites are sedimentary formations created by the layered growth of microorganisms in shallow marine settings. Fossil stromatolites constitute some of the earliest evidence for life on Earth. Allen Nutman
et al
. describe metamorphosed stromatolites deposited around 3,700 million years ago in what is now Greenland. This is more than 200 million years older than the previous record-holders for earliest-known fossils, so these stromatolites rank as the Earth's earliest fossils by some margin. Although there is indirect evidence from isotope geochemistry that the pedigree of life on Earth is even older, this report is likely to be controversial.
Biological activity is a major factor in Earth’s chemical cycles, including facilitating CO
2
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
1
,
2
from the Isua supracrustal belt (ISB), southwest Greenland
3
. 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. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia
4
,
5
. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO
2
sequestration by 3,700 million years ago (Ma), near the start of Earth’s sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life’s origin in the Hadean eon (>4,000 Ma)
6
.
Publisher
Nature Publishing Group UK,Nature Publishing Group
Subject
/ Earth
/ Fossils
/ Geologic Sediments - microbiology
/ Humanities and Social Sciences
/ Isotopes
/ letter
/ Life
/ Science
/ Seawater
/ Yttrium
