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Fossils: Evidence for life in 3.95-billion-year-old rocks


September 28, 2017

Analysis of carbon isotope compositions of carbonaceous material and carbonate from sedimentary rocks in northern Labrador, Canada, suggests that organic life may have existed on Earth as early as 3.95 billion years ago. The findings, reported in Nature this week, might represent some of the earliest known life on Earth.

Evidence for the presence of life early in Earth’s history remains sparse owing to the scarcity and poor preservation of rocks from the Eoarchean era (about 3.6 to 4 billion years ago). Isotope analysis of sedimentary rocks in the Isua supracrustal belt in southwestern Greenland, which date to 3.7 to 3.8 billion years ago, suggests that graphite grains therein may be biogenic (produced by living organisms). However, biogenic graphite has not been discovered in recently studied rock formations of a similar age in Akilia, Greenland, and Nuvvuagittuq, Canada.

Tsuyoshi Komiya and colleagues studied graphite in the oldest known metasedimentary rocks from Saglek Block in northern Labrador, Canada, which are about 3.95 billion years old. They carried out a detailed geological analysis of the rocks and measured the concentrations and isotope compositions of the graphite and carbonate. They find that the graphite is biogenic, and note that the consistency between crystallization temperatures of the graphite and the metamorphic temperature of the host rocks indicates that the graphite does not originate from later contamination.

The authors suggest that the discovery of biogenic graphite in these rocks may enable the geochemical study of the organisms that produced the graphite and that this could yield further insights into early life on Earth.

doi: 10.1038/nature24019

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