Earth is a place teeming with life, even in the most extreme conditions. Life on our planet is characterized by adapting to the most extreme environments. There is life even in deserts, in the craters of volcanoes or on the frozen wastelands.
Dallol, in Ethiopia’s Danakil Depression, is one such hostile place. This volcanic plain is located on a large accumulation of lava. There are highly acidic hot springs, with a temperature between 90 ° C and 110 ° C.
Until now, this place was considered a good setting to emulate extreme environments comparable to those of Mars, and analyze if life could thrive in such conditions. A few months ago, a study by the Center for Astrobiology (CAB, INTA-CSIC), and published in the journal Nature Scientific Reports, identified thermo-halo-acidophilic microorganisms (which adapt well to high temperatures) within mineral deposits buried in one of the seabed of the Ethiopian volcano. But now, a French-Spanish team from the National Center for Scientific Research (CNRS) has concluded that no: microbial life is absent. At least, there is no sign of it neither in the salty, hot and hyperacid pools, nor in the salty and magnesium-rich lakes, as detailed by the researchers, in an article published in the journal Nature Ecology & Evolution.
The team sequenced microorganism classification genetic markers, attempted microbial culture, tried to identify individual cells, and performed chemical analysis of the brines and scanning electron microscopy combined with X-ray spectroscopy.
Finally, the scientists identified two physicochemical barriers to life in the presence of surface liquid water. The first one, the abundance of chaotropic magnesium salts (an agent that breaks hydrogen bonds and denatures biomolecules); second, the combination of hypersalinity, hyperacidity and high temperature conditions.
They look like microorganisms, but they are not
Based on these conclusions, why did a previous study affirm the existence of life in the ancient sea beds of this volcanic area of Ethiopia? As published by the SINC Agency, in the statements of the main researcher, Purificación López García, the explanation lies in a misinterpretation of the data : “Some silica-rich Dallol mineral precipitates may appear to be microbial cells under the microscope. These mineral particles could have been interpreted as fossilized cells, when in fact they form spontaneously in the brines even though there is no life ”.
These results lead to a key conclusion: that not only the presence of water is an indicator of life, but chemical conditions or temperature are key determinants that can make a place completely sterile for the presence of microorganisms.
The conclusions of this work also invite us to be cautious when looking for life , not only on Earth, but outside of it. As the researchers detail: “The study helps to circumscribe the limits of habitability and demands caution when interpreting morphological biosignatures on Earth and beyond.” That is to say: we must be cautious when evaluating an apparently cellular structure as ‘life’, since it could have an abiotic origin.
Studies on the hydrothermal system of Dallol, in Ethiopia, considered the hottest ecosystem in the world , allow scientists to emulate the conditions of an early red planet (due to its volcanic origin and the presence of basaltic materials), Mars from three years ago. billion years. However, the new results are unflattering about the possibility that our neighbor has harbored life in the past, assuming that its conditions were one day as extreme as those of this place, as scientists believe.
More information:
Jodie Belilla, David Moreira, Ludwig Jardillier, Guillaume Reboul, Karim Benzerara, José M. López-García, Paola Bertolino, Ana I. López-Archilla & Purificación López-García. “Hyperdiverse archaea near life limits at the polyextreme geothermal Dallol area.” Nature Ecology & Evolution 3: 1552–1561, October 28, 2019.
