The oldest life trace on Earth may have been found in Canada.
If the conclusions of the work done by the Japanese researchers Tsuyoshi Komiya and Yuji Sano of the University of Tokyo are confirmed, these evidence would be one of the oldest proofs of life on Earth.
Last March, geochemist Dominic Papineau of the University College of London and Canadian colleagues reported the discovery of certain structures in Nuvvuagittuq rocks on the eastern shore of Hudson Bay in Quebec. They are fossilized micro-organisms that date back at least 3.8 billion years.
The Earth was formed 4.56 billion years ago. According to some scientists, several types of micro-organisms could have populated it very early in its evolution.
In the papers published in Nature magazine, the researchers analyzed rock samples they collected between 2011 and 2013 from the Saglek Block area.
The researchers analyzed the isotopic composition of graphite grains (carbon) to determine whether it was organic or not. Isotopes are atoms which possess the same number of protons, but which differ in their number of neutrons.
The carbon has several natural isotopes (including the famous carbon 14, used for dating, but not found in ancient rocks).
In this study, researchers were interested in the ratio of carbon 13 (6 protons, 7 neutrons) and carbon 12 (6 protons, 6 neutrons), two stable isotopes.
Their results show that the grains of graphite were markedly enriched with carbon.
The Japanese researchers deduce that the “signature” of this graphite is biogenic, that is to say that it comes from living organisms.
The geochemist Sylvain Bernard, of the National Museum of Natural History of France, however, is very cautious about these conclusions. “It is not only living beings who has this isotopic signature. It can come from mineral reactions or fluid reactions between them,” he said.
According to Bernard, the arguments put forward by the Japanese team are far from being sufficient to determine clearly the biogenicity of these graphites. “They use arguments that may be necessary, but are not enough,” explains Sylvain Bernard.
“For the moment, we still do not know when or how life has appeared on Earth. But we are making progress thanks to advanced techniques.”
In September 2016, an Australian team of researchers had announced the discovery of stromatolites (3.7 billion years old stromatolite structures formed by microbial colonies) in Greenland.