Several forms of microbial life would have existed quite early on Earth

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Several forms of microbial life would have existed quite early on Earth

Dominic Papineau holds a sample of rock estimated to be 4.28 billion years old.

Diverse microbial life existed on Earth at least 3.75 billion years ago, tends to show the work of scientists associated with the University College of London (UCL), UK.

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Structures composed of red hematite forming a stem with parallel branches on one side that measure almost a centimeter long

To reach this conclusion, exobiologist Dominic Papineau and his colleagues analyzed a rock from the Nuvvuagittuq belt, located on the coast of Hudson Bay, Quebec. This rock formation is known to contain the oldest sediments in the earth's crust.

Using many different lines of evidence, our study strongly suggests that a number of different types of bacteria existed on Earth between 3.75 and 4.28 billion years ago, says Professor Papineau.

  • The Nuvvuagittuq belt was once a piece of floor oceanic.
  • It contains some of the oldest known sedimentary rocks on Earth.
  • These rocks are believed to have been deposited near a system of hydrothermal vents, where cracks in the ocean floor allow heated iron-rich waters to pass through by magma.

As early as 2017, a team including Dominic Papineau had published in the journal Naturea study describing structures in rock from the same belt that most likely belonged to fossilized microorganisms dating between 3.8 and 4.3 billion years ago.

This estimate pushed back the oldest known traces of life on Earth by 100 million or even 600 million years. It was quickly challenged by other scientists who were not convinced that the structures observed were indeed of biological origin. According to them, the tiny hematite filaments, knobs and tubes observed in the rock could only be organic, that is to say created by chemical reactions.

In the current work, Professor Papineau and his team analyzed a rock from the same belt in more detail.

“We cut the rock into sections about as thick as paper [100 microns] in order to closely observe the tiny fossil structures, which are made of hematite, a form of carbon dioxide. iron or rust, and encased in quartz. ”

— Dominic Papineau

These slices of rock were more than twice as thick as the previous sections that the researchers had cut [in 2017], adds Professor Papineau.

Red chert is a rock rich in iron and silica. It would contain tubular and filamentous microfossils. This sedimentary rock is in contact with dark green volcanic rock (top right). It was present not far from the hydrothermal vents on the ocean floor.

Researchers found a much larger and more complex hematite structure there.

“This structure forms a stem with parallel branches on one side that is nearly a centimeter long. There are also hundreds of distorted spheres […] associated with the tubes and filaments which often end in a corkscrew. »

— Dominic Papineau

Professor Papineau acknowledges that some of these structures may have arisen as a result of chemical reactions, but he believes that the tree-like stem with parallel branches is most likely of biological origin. According to him, no structure created solely by non-biological chemistry has been found like this, either in the laboratory or in nature.

Dominic Papineau in the field

In addition, the UCL team compared the observed structures to more recent fossils, but also to iron-oxidizing bacteria located near present-day hydrothermal vent systems.

“We have found modern equivalents of twisted filaments, parallel branching structures and distorted spheres, for example near the submarine volcano Loihi, off Hawaii. »

— Dominic Papineau

This work also provides evidence that bacteria draw their energy from different sources. Indeed, researchers have found mineralized chemical byproducts in the rock that correspond to ancient microbes living on iron, sulfur and possibly also carbon dioxide and light through a form of photosynthesis not involving no oxygen.

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Prior to 2017, the oldest fossils had been found in Australia and dated to 3.46 billion years ago. Again, scientists disputed the biological nature of microfossils.

Published in the journal Science Advances (in English), the results of this study lead scientists to believe that a variety of microbial life already existed on early Earth.

“This means that life could have started as soon as 300 million years after the formation of the Earth. In geological and astronomical terms, it's fast! This is approximately one revolution of the Sun around the galaxy. »

— Dominic Papineau

The scientist draws a parallel between his conclusions and the search for extraterrestrial life, for example on Mars and on the moons of Saturn and Jupiter ( like Enceladus or Europe).

“Our data open up several avenues of investigation in terms of the evolution of metabolisms. At the biological level, we really push back the complexity of microorganisms, which tells us about the origin of life.

— Dominic Papineau

These findings have implications for the possibility of extraterrestrial life. If life is relatively quick to emerge, given the right conditions, it increases the likelihood that life exists on other planets, Professor Papineau continues.

This gives us an idea of ​​the recipe for what to look for, how to look for it and how to identify it, summarizes the researcher.

Life on Earth

  • 4.568 billion years ago: the formation of the Earth
  • From 4.3 to 3.8 billion years ago: the oldest forms of life, discovered by Prof. Papineau's team
  • 600 million years ago: the first multicellular animals
  • 385 million years ago: the oldest fossilized tree
  • 230 million years ago: the appearance of the dinosaurs
  • 65 million years ago: the extinction of the dinosaurs allowing the proliferation of mammals
  • 6 million years: the separation of the line of hominids and great apes; humans begin to move on their two legs.

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