Layer-deflecting bright red concretion of haematitic chert (an iron-rich and silica-rich rock), which contains tubular and filamentous microfossils. This co-called jasper is in contact with a dark green volcanic rock in the top right and represent hydrothermal vent precipitates on the seafloor. Nuvvuagittuq Supracrustal Belt, Québec, Canada. Canadian quarter for scale.
Credit: D. Papineau.
Scientists from University College, London (UCL) and State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan, China, believe they may have found evidence of the earliest life on earth, from just 300 million years after its formation.
The traces of bacterial deposits were found in rocks from Quebec’s Nuvvuagittuq Supracrustal Belt which are believed to have been formed in hydrothermal vents - regarded as the most likely place for the formation of organised, self-replicating, biotic systems from inorganic sources.
The evidence is in the form of tubes, branching filaments and ellipsoids of haematite, very similar to structures formed today by chemosynthetic bacteria in hydrothermal vents such as those close to the Loihi undersea volcano near Hawaii, as well as other vent systems in the Arctic and Indian oceans. Although the scientists concede that these structures could conceivably be the result of chance chemical reactions, no structures like these that are the result of chemical reactions have ever been found.
The UCL press release which accompanied the team's open access publication in Science Advances explains the technique used to examine the microfossils:
The research team sliced the rock into sections about as thick as paper (100 microns) in order to closely observe the tiny fossil-like structures, which are made of haematite, a form of iron oxide or rust, and encased in quartz. These slices of rock, cut with a diamond-encrusted saw, were more than twice as thick as earlier sections the researchers had cut, allowing the team to see larger haematite structures in them.Observing that the structures were better preserved in the finer, less highly metamorphosed, quartz than in the coarser, more metamorphosed quartz, the team concluded that the fine structures could not have been the result of rock metamorphosis during which it would have been heated and squeezed. They also showed that the levels of rare earth elements in the micro fossil-bearing rock was the same as that in other ancient rock sediments, showing that the fossil-bearing rock was not a later intrusion.
They compared the structures and compositions to more recent fossils as well as to iron-oxidising bacteria located near hydrothermal vent systems today. They found modern-day equivalents to the twisting filaments, parallel branching structures and distorted spheres (irregular ellipsoids), for instance close to the Loihi undersea volcano near Hawaii, as well as other vent systems in the Arctic and Indian oceans.Using many different lines of evidence, our study strongly suggests a number of different types of bacteria existed on Earth between 3.75 and 4.28 billion years ago.
This means life could have begun as little as 300 million years after Earth formed. In geological terms, this is quick – about one spin of the Sun around the galaxy.
Dr Dominic Papineau, lead author
Department of Earth Sciences
And London Centre for Planetary Sciences
University College London, London, UK.
And School of Earth Sciences
China University of Geosciences, Wuhan, China.
As well as analysing the rock specimens under various optical and Raman microscopes (which measure the scattering of light), the research team also digitally recreated sections of the rock using a supercomputer that processed thousands of images from two high resolution imaging techniques. The first technique was micro-CT, or microtomography, which uses X-rays to look at the haematite inside the rocks. The second was focused ion beam, which shaves away miniscule - 200 nanometre-thick - slices of rock, with an integrated electron microscope taking an image in-between each slice.
Both techniques produced stacks of images used to create 3D models of different targets. The 3D models then allowed the researchers to confirm the haematite filaments were wavy and twisted, and contained organic carbon, which are characteristics shared with modern-day iron-eating microbes.
The team's paper, which many Young-Earth Creationists may find distressing if they find the courage to read it, was published, open access in Science Advances:
AbstractThis discovery strongly suggests that early bacteria may have formed some time before the previous oldest (disputed) evidence of early life found in rocks in Western Australia dated to 3.46 billion years ago. If confirmed, this evidence of bacterial activity only some 300 million years after the formation of earth, suggests that abiogenesis was not as difficult as some may think and that once independent, self-replicating early life got started, it quickly diversified into several different species of bacteria.
The oldest putative fossils occur as hematite filaments and tubes in jasper-carbonate banded iron formations from the 4280- to 3750-Ma Nuvvuagittuq Supracrustal Belt, Québec. If biological in origin, these filaments might have affinities with modern descendants; however, if abiotic, they could indicate complex prebiotic forms on early Earth. Here, we report images of centimeter-size, autochthonous hematite filaments that are pectinate-branching, parallel-aligned, undulated, and containing Fe2+-oxides. These microstructures are considered microfossils because of their mineral associations and resemblance to younger microfossils, modern Fe-bacteria from hydrothermal environments, and the experimental products of heated Fe-oxidizing bacteria. Additional clusters of irregular hematite ellipsoids could reflect abiotic processes of silicification, producing similar structures and thus yielding an uncertain origin. Millimeter-sized chalcopyrite grains within the jasper-carbonate rocks have 34S- and 33S-enrichments consistent with microbial S-disproportionation and an O2-poor atmosphere. Collectively, the observations suggest a diverse microbial ecosystem on the primordial Earth that may be common on other planetary bodies, including Mars.
Papineau, Dominic; She, Zhenbing; Dodd, Matthew S.; Iacoviello, Francesco; Slack, John F.; Hauri, Erik; Shearing, Paul; Little, Crispin T. S.
Metabolically diverse primordial microbial communities in Earth’s oldest seafloor-hydrothermal jasper
Science Advances 8(15); DOI: 10.1126/sciadv.abm2296
Copyright: © 2022 The authors. Published by the American Association for the Advancement of Science
Open access
Reprinted under a Creative Commons Attribution-NonCommercial 4.0 International license (CC BY-NC 4.0)
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