Sacred getting old for the origin of life on Earth. Australian geologists have discovered Greenland traces of microbial activity dating back 3.7 billion years, two hundred million more than the previous record found in rocks from Australia or South Africa. And 800 million years only after the formation of the Earth.
“It’s crazy! We did not think that such indices were able to survive so long “ says Allen Nutman, professor of Wollongong University, first author of the study published in Nature Thursday 1 st September reporting the discovery.
you had to have the expert eye of the researcher and his colleagues from the University of New South Wales, who roam the land from Greenland the 1980 to identify very specific forms in a flush rock, visible only in the summer after the snow melts. It is located in the greenstone belt Isua, on an island in the southwest of Greenland, geological structures whose age was determined by isotopic dating.
organic sticky carpet
The treasure is only a few dozen centimeters, “engraved” on an area of 2 meters wide. It has the form of a succession of pointed cones and bumps crushed brown, resting on a kind of bluish yarrow; the whole being covered with layers of new rainbow rock. Experts speak of stromatolites and attribute these forms of microorganisms. These, by changing their surroundings, allow precipitation of thin films of carbonates (limestone of the family), which over time are superimposed and form these structures, which are also found in coral reefs. Stromatolites are not strictly speaking fossils that record them directly in the form of organisms.
These ancient microbes are nearly as complex as corals . You should see them rather as forming a sort of organic sticky mats, deposited in shallow bodies of water. Their metabolism enabled them to assimilate CO 2 in the atmosphere, most abundant gas at the time, to turn it into carbonate. These primitive cells had probably not even need to solar energy, that is to say, photosynthesis, to achieve these chemical reactions. “These stromatolites are created by colonies of microorganisms. In those early times, so there was a kind of collaboration. Life already had a long history! “, says Allen Nutman, thus potentially pushing farther in time the arrival of a first living cell on Earth.
Provided, however, to confirm this study. Because the scientific community has taken years to agree on the criteria to examine whether stromatolites are organic or not. Such forms may indeed occur naturally under the effect of folds of sedimentary soil, for example. One of these criteria is to look microscopic bumps and identifying purposes “leaves” inside. They are present in these rocks from Greenland, as in those “younger” South Africa or Australia.
“This is a powerful biological indicator, even if these sheets are less visible than those previously found in Australia “, admits Kevin Lepot, professor at the University of Lille, which has inspected other stromatolites. In the article by Nature with the discovery, Abigail Allwood, NASA, described the implications of the discovery of “amazing” . With his sharp eye, it also notes that the sediments seem to have deposited between the bumps, another index for a biological origin. “But that will not stop the controversy” , which provides that, in the mid-2000s, has contributed greatly to clarify the origin of stromatolites older than 3.4 billion years.
the interest of Mars missions revived
Pascal Philippot, of the Institute of earth physics of Paris, also notes that these stromatolites Greenland are present only over a very short distance, whereas in Australia for example, they run over several hundred kilometers. Ironically, Allen Nutman had already announced in 1996 have found evidence of life 3.7 billion years in rocks from another region of Greenland and unrelated stromatolites. Ten years later, he returned to his hypothesis. Before then, by other evidence, renfoncer of the nail. “We believe we have good evidence. Everyone can watch and study the “, says the researcher.
To gain certainty, we should find other stromatolites, what hope the team if it gets the funding for new expeditions. However, there is little hope of finding clues proving more directly biological, like Kevin Lepot team and Pascal Philippot had been able to do in 2008 on Australian stromatolites older than 2.7 billion years. They had discovered small globules of organic material associated with calcium carbonate nanocrystals, impossible to manufacture by physicochemical processes.
Unfortunately, the history of Greenland rocks opposed to a priori such a find. They are metamorphic effect, that is to say, they were buried under kilometers of other rocks and under mountain ranges, pushing their temperature to over 500 degrees Celsius, before being deformed by various landslides. They ended up back on the surface, but these processes have irrevocably changed their chemical composition.
Still, this leap in time 200 million years is a horizon that many researchers had in mind . It proves that life could appear very early on Earth, in difficult conditions, with an oxygen-free atmosphere, an intense bombardment of meteorites, destructive sunlight … This revived interest of Mars missions that explore terrain that age corresponds precisely to that of rocks studied Greenland. Robots could find traces more visible and numerous than some centimeter bumps uncovered on Earth
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