Various life forms evolved 3.75 billion years ago – challenging the conventional view of when life began

Development of the artist’s concept in early life.

Different life forms may have evolved earlier than previously thought.

Diverse microbial life existed on Earth at least 3.75 billion years ago, suggests a new study led by University College London (UCL) researchers that challenges the conventional view of when life began.

Diverse microbial life existed on Earth at least 3.75 billion years ago, suggests a new study led by UCL scientists that challenges the conventional view of when life began.

For the study, published in The progress of science, the research team analyzed a stone the size of a fist from Quebec, Canada, estimated to be between 3.75 and 4.28 billion years old. In a former Nature paper, the team found small filaments, buds and tubes in the rock, which appeared to be made of bacteria.

Oldest microfossils on earth

Centimeter-sized pectinate-branched and parallel-aligned filaments composed of red hematite, some with twists, tubes, and various kinds of hematite spheroids. These are the oldest microfossils on Earth that lived on the ocean floor near hydrothermal vents, and they metabolized iron, sulfur, and carbon dioxide. Nuvvuagittuq Supracrustal Belt, Quebec, Canada. Credit: Dominic Papineau

However, not all scientists agreed that these structures – dating back some 300 million years earlier than what is more commonly accepted as the first sign of ancient life – were of biological origin.

Now, after extensive further analysis of the rock, the team has discovered a much larger and more complex structure – a stem with parallel branches on one side that is almost an inch long – as well as hundreds of distorted spheres or ellipsoids next to tubes and filaments .

The researchers say that while some of the structures may have been created through random chemical reactions, the “tree-like” stem with parallel branches was most likely of biological origin, as no structure created via chemistry alone has been found similar to it.

Old rock containing microfossils

Layer-deflecting bright red concretion of hematic chert (an iron-rich and silica-rich rock), which contains tubular and filamentous microfossils. This so-called jasper is in contact with a dark green volcanic rock at the top right and represents hydrothermal vents on the seabed. Nuvvuagittuq Supracrustal Belt, Quebec, Canada. Canadian quarter for scale. Credit: Dr. Papineau

The team also provides evidence of how the bacteria got their energy in different ways. They found mineralized chemical by-products in the rock, which are consistent with old microbes that feed on iron, sulfur and possibly also carbon dioxide and light through a form of photosynthesis that does not involve oxygen.

These new findings suggest, according to scientists, that a variety of microbial lives may have existed on the original Earth, potentially as little as 300 million years after the planet’s formation.

Three-dimensional micro-CT reconstruction of two parallel aligned twisted filaments made of hematite. (The red and green colors represent hematite in different concentrations.) This comes from a column made of the jasper knot in the Nuvvuagittuq band iron formation. Credit: Francesco Iacoviello

Main author Dr. Dominic Papineau (UCL Earth Sciences, UCL London Center for Nanotechnology, Center for Planetary Sciences and China University of Geosciences) said: “Using many different lines of evidence, our study strongly suggests that a number of different types of bacteria existed on Earth for between 3.75 and 4.28 billion years ago. “

“This means that life could have begun as little as 300 million years after the formation of the Earth. In geological terms, this is fast – about a spin of the Sun around the galaxy.”

“These results have implications for the possibility of extraterrestrial life. If life is relatively quick to emerge, given the right conditions, this increases the chance that life exists on other planets.”

For the study, the researchers examined rocks from Quebec’s Nuvvuagittuq Supracrustal Belt (NSB), which Dr. Papineau collected in 2008. NSB, once part of the ocean floor, contains some of the oldest sedimentary rocks known on Earth, believed to have been laid down. near a system of hydrothermal vents, where cracks on the seabed escape through iron-rich water heated by magma.

Dr.  Papineau Holding Rock Sample

Dr. Dominic Papineau holds a sample of the rock, estimated to be up to 4.28 billion years old. Credit: UCL / FILMBRIGHT

The research team cut the rock into sections about as thick as paper (100 microns) to closely observe the tiny fossil-like structures made of hematite, a form of iron oxide or rust, and encapsulated in quartz. These cutting discs, cut with a diamond-coated saw, were more than twice as thick as previous sections that the researchers had cut, allowing the team to see larger hematite structures in them.

They compared the structures and compositions with newer fossils as well as with iron-oxidizing bacteria located near hydrothermal vents today. They found modern equivalents to the twisted filaments, parallel branched structures, and distorted spheres (irregular ellipsoids), for example, near the Loihi subsea volcano near Hawaii, as well as other vent systems in the Arctic and Indian Oceans.

In addition to analyzing the sample samples under various optical and Raman microscopes (which measure the scattering of light), the research team also digitally recreated sections of the clip using a supercomputer that processed thousands of images from two high-resolution image processing techniques. The first technique was micro-CT or microtomography, which uses X-rays to look at the hematite inside the rocks. The other was a focused ion beam, which shaves small – 200 nanometer thick – slices of stone, with an integrated electron microscope that takes a picture between each slice.

Both techniques produced stacks of images that were used to create 3D models of different dimensions. The 3D models then allowed the researchers to confirm that the hematite filaments were wavy and twisted and contained organic carbon, which are properties shared with today’s iron-eating microbes.

In their analysis, the team concluded that the hematite structures could not have been created through compression and warming of the rock (metamorphosis) over billions of years, and pointed out that the structures appeared to be better preserved in finer quartz (less affected by metamorphosis)) than in the coarser quartz (which has undergone more metamorphosis).

The researchers also looked at the levels of rare earth elements in the fossil-laden rock and found that they had the same levels as other ancient rock samples. This confirmed that the seabed deposits were as old as the surrounding volcanic rocks, and not younger deceptive infiltrations, as some have suggested.

Prior to this discovery, the oldest fossils previously reported were found in Western Australia and dated to 3.46 billion years old, although some scientists have also disputed their status as fossils, claiming that they are of non-biological origin. .

Reference: “Metabolically diverse primordial microbial communities in Earth’s oldest seabed hydrothermal jasper” by Dominic Papineau, Zhenbing She, Matthew S. Dodd, Francesco Iacoviello, John F. SlackErik Hauri, Paul Shearing, and Crispin TS Little, April 13, 2022, The progress of science.
DOI: 10.1126 / sciadv.abm2296

The new study involved researchers from UCL Earth Sciences, UCL Chemical Engineering UCL London Center for Nanotechnology and Center for Planetary Sciences at UCL and Birkbeck College London, as well as from the US Geological Survey, Memorial University of Newfoundland in Canada, Carnegie Institution of Science, University of Leeds and China University of Geoscience in Wuhan.

The research received support from UCL, Carnegie in Canada, Carnegie Institution of Science, China University of Geoscience in Wuhan, National Science Foundation of China, Chinese Academy of Sciences and the 111 project in China.

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