Biological activity is a major factor in Earth’s chemical cycles, including facilitating CO2 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 minerals1, 2 from the Isua supracrustal belt (ISB), southwest Greenland3. 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, Australia4, 5. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 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.
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Extended data figures and tables
Extended Data Figures
- Extended Data Figure 1: Geological map and location of the described localities A, B and C. (785 KB)
a, Geological map covering the described localities. The outcrops for localities A, B and C are indicated. b, Position of locality in the ISB. c, Panoramic view towards the southeast over the described localities. In the foreground are the banded iron formation and chert outcrops in the northwest corner of the map a. The 15–20 m thick Ameralik dyke forms the skyline.
- Extended Data Figure 2: Background information on the preservation of sedimentary structures and overviews of the outcrops A and B. (1,177 KB)
a, Thin section of calc–silicate rocks ~5 m south of site A. The strain is still low, but there was ingress of an H2O-rich fluid phase during metamorphism. Tremolite (green) is developed extensively in the left-hand side of the section, from a reaction between dolomite and quartz in the presence of the H2O-rich fluid. The original sedimentary layering (vertical within the slide) is severely disrupted by the tremolite growth, with development of a foliation orientated from lower left to upper right. b, Thin section from site B where quartz and dolomite are still in equilibrium because a CO2-rich fluid phase was maintained during metamorphism. Fine-scale sedimentary structures are preserved (approximately horizontal across the slide). Foliation is absent. Both thin sections are shown at the same scale and are approximately 2 cm wide. c, Overview of site A. Image inverted because outcrop is in an overturned fold limb. The red rectangle is the area shown in Fig. 1a, b. The two red parallel lines indicate the sawn block in Extended Data Fig. 4.The red arrows point to three layers with stromatolites. Field of view is 2 m. d, Overview of site B. The detailed area shown in Fig. 2b, c is indicated by a red arrow.
- Extended Data Figure 3: Imaging of a locality A stromatolite. (581 KB)
Stromatolite structure from site A. a, SEM backscattered electron image of an area near the top of the stromatolite shown in c. Variation in brightness is governed by quartz (duller) versus dolomite (brighter) grains. A subtle millimetre-scale layering is visible running horizontally across the image, that is, parallel to the top of the stromatolite. This was investigated further by examining the relative greyscales of the pixels forming the right-hand side of the image (red box in a). The other side of this image was not used in pixel analysis, because of the black field (beyond the edge of the scanned sample). b, Variation in grey scale. c, Sampling sites for carbonate oxygen and carbon isotope analysis (Extended Data Table 3).
- Extended Data Figure 4: Locality A stromatolite sawn blocks. (1,104 KB)
Locality A sawn block. a, Montage of four sides of block. b, Sampling site pre- and post-removal of block. c, Location of analyses A-1 to A-11 (Extended Data Table 2). Note the onlap of this horizontal bedding to the stromatolite margin on the first block side. d, X-ray fluorescence ITRAX scans of a locality A stromatolite culmination and the laterally equivalent horizon. Scans are given as relative counts per second on the relevant X-ray peak. This shows the featured stromatolite layer (‘d’ on the image of the rock slice) has much lower Ti and K abundances (denoting the phlogopite proxy for a lower mud content) compared with the layers above and below.