Unprecedented rains decimate surface microbial communities in the hyperarid core of the Atacama Desert

Centro de Astrobiología (CSIC-INTA)
  • Rains in recent years decimate the species of microorganisms in the driest desert on Earth
  • Extinctions of up to 85% of the species take place
  • Related parallels are traced between  causes of Atacama and Mars orography

 

Atacama: the setting for a microscopic extinction

The Atacama Desert covers a 1000-km long strip of land in northern Chile. Depending on the estimates, it has an extension of between 105,000 km2 and 128,000 km2. A territory of sand, stony terrain, salt lakes, and magmatic terrain from the coast until the Andes mountain range, the Atacama Desert has been termed the driest and oldest desert on Earth. At its core, it contains some of the most hyperarid soils on the planet.

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The conditions at Atacama result in some of the most hyperarid environments on Earth, approaching aspects of planet Mars.

There, for at least the previous 500 years there had been no rain. This changed, however, in recent years. Rain episodes were recorded for the first time in the hyperarid soil of Atacama. Surprisingly, the sudden abundance of water was devastating for the existing microbial life. That was the conclusion of a study published in Nature Scientific Reports by an international group of researchers from the Centro de Astrobiología (CAB, CSIC-INTA).

For scientists, these unexpected rains could be attributed to global climate change. In the context of the Atacama Desert, contrary to what could have been expected, the presence of water has not meant the flourishing of life in the Atacama desert. Much on the contrary, the rains have caused huge devastation in the microbial species present before the rainfall.

According to the results, the high rainfall has caused a mass extinction event of most of the indigenous microbial species. The extent of this extinction reached levels of up to 85% of these species. Such high mortality rates came as a result of the osmotic stress caused by the sudden abundance of water. Native microorganisms, perfectly adapted to live under extreme dryness conditions and optimized to extract the scarce environmental humidity, have been unable to cope with the sudden flooding, dying as a result under the water-excess conditions.

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Images of bacterial species identified in the Atacama lagoons (left) and phylogenetic diagram (right), from original article.

The study represented a breakthrough in understanding the microbiology of extreme arid environments and presented a new paradigm to understand the evolutionary route of the hypothetical early Martian microbiota.

 

A step forward in the microbiology of extreme arid environments

Mars, a hyperarid planet, also experienced catastrophic floods in ancient times. Mars had a first period, the Noachian (between 4.5 and 3.5 billion years ago), in which there was a lot of water on its surface. We know that from preserved hydrogeological evidences, in the form of ubiquitous hydrated minerals on the surface, traces of rivers, lakes, deltas and a possible hemispheric ocean in the northern plains. Later on, Mars lost its atmosphere and hydrosphere and became the dry and arid world that we know today.

However, during a later period, the Hesperian (from 3.5 to 3 billion years ago), large volumes of water dug the surface of Mars and formed overflow channels, the largest found in the Solar System. If there were still microbial communities living under extreme desiccation conditions, they would have undergone osmotic stress processes similar to those observed in Atacama.

A possibility that arises from the Atacama study conclusions is that, possibility, the recurrence of liquid water on Mars could have contributed to the extinction of Martian life, if it ever existed, rather than become an opportunity for the re-flowering of resilient microbiota.

 

Nitrogen in the soil -parallels with Atacama

The Atacama study notes that large deposits of nitrates in the Atacama Desert offer evidence of long periods of extreme dryness in the past. The nitrates became concentrated at valley bottoms and former lakes by sporadic rains about 13 million years ago. Nitrates happen to be suitable nutrients for certain microbes.

The Atacama nitrates may represent a convincing analogue to the nitrate deposits that were discovered on Mars by the rover Curiosity (as reported in a 2015 study about evidence of indigenous nitrogen in Martian solid samples, in the Proceedings of the National Academy of Sciences).

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The rover Curiosity provided data about the presence of nitrogen in the form of nitrates at the Martian surface.

Earlier on, CAB researcher Fairén and colleagues published in Nature Astronomy another, related work. The researchers investigated the formation of clay during brief periods of warmer, wetter conditions in ancient Mars. They discovered the sporadic appearance of short-lasting wet environments in early Mars, also then a generally hyperdry planet. This finding, in part, could contribute to explain the observed Martian mineralogy.

Altogether, the long periods of dryness followed by short wet periods, could have been in the origin of the nitrate deposits on Mars, similar to those deposits found in the Atacama Desert. Among others, the combined understanding of mineralogy, climate or chemistry at extreme sites on Earth (as the Atacama Desert) has shown that it allows to obtain a better understanding of the past and present of Mars. With several nations planning missions to Mars, the planet will certainly remain in the spotlight of planetary exploration in the future to come, along with the research.

 

Image credits:

Atacama Desert landscape is in the public domain and was downloaded from Pixabay.

Atacama microorganisms figure was downloaded and modified (cropped and cleaned from text elements) from the original research article at Nature, and was licensed via an Attribution 4.0 International (CC BY 4.0) license.

Rover Curiosity picture is in the public domain and was downloaded from Pixabay.

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