The Earth is a place full of life, even in the most extreme conditions. Life on our planet is characterised by adapting to the most extreme environments. There is life even in deserts, in the craters of volcanoes or in the frozen wastelands.
Dallol is a hostile environment deep in the depression of Danakil, Ethiopia. This volcanic plain is situated on a large accumulation of lava where there are acidic hot springs between the temperature of 90°C and 110°C.
A few months ago, a study conducted by the Center for Astrobiology (CAB, INTA-CSIC), identified thermo-halo-acidophilic microorganisms (that adapt well to high temperatures) within mineral deposits buried in one of the seabeds of the Ethiopian volcano.
However, new research conducted by a French-Spanish team from the National Center for Scientific Research (CNRS) concluded that microbial life is absent. At the very least, there is no sign of it either in salty, hot, hyperacid pools or in salty, magnesium-rich lakes, as researchers detail in an article published in Nature Ecology & Evolution.
The team sequenced genetic markers to classify microorganisms, 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. Firstly, the abundance of chaotropic magnesium salts (an agent that breaks the hydrogen bridges and denatures the biomolecules); and secondly, the combination of conditions of hypersalinity, hyperacidity and high temperature.
They look like microorganisms, but they are not.
According to these conclusions, why did a previous study assert the existence of life on the ancient seabed of this Ethiopian volcanic zone? As published by the SINC Agency, the principal investigator, Purificación López García, claims that the explanation lies in a misinterpretation of the data: "Some Dallol mineral precipitates rich in silica may look like microbial cells to the microscope. These mineral particles may have been interpreted as fossilised cells, when in fact they spontaneously form in brines even though there is no life.
These results lead to a key conclusion: that not only is the presence of water an indicator of life, but that chemical conditions or temperature are key conditioning factors that can make a place completely sterile for the presence of microorganisms.
The conclusions of this work, invite you to be prudent when looking for life, not only on Earth, but also outside it. "The study helps to circumscribe the limits of habitability and demands caution when interpreting morphological biofirms on Earth and beyond. In other words, we must be cautious when evaluating an apparently cellular structure as 'life', since it could have an abiotic origin,” the researchers explain.
Studies of the Dallol hydrothermal system in Ethiopia, consider it as the world's warmest ecosystem. It allows scientists to emulate the conditions of a primitive red planet (due to its volcanic origin and the presence of basaltic materials), the Mars of three billion years ago. However, the new results are unflattering about the possibility that our neighbour has harboured life in the past, assuming that their conditions were one day as extreme as those of this place, as scientists believe.
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, 28 October 2019.