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After experiencing significant rainfall for at least 500 years, the Atacama Desert in Chile finally receives rains. Quite unexpectedly, however, these rains – instead of favoring life – do exactly the opposite.
Life on Earth can not exist without water, but for microbes highly adapted to arid conditions, the sudden introduction of excess water can be totally devastating. This is the conclusion of a new article published this week in Scientific Reports. Fascinating, these findings, while applicable to life on Earth, may also apply to ancient Mars, a planet that is likely to favor microbial life in its ancient past, but also susceptible to flooding. catastrophically.
Located in northern Chile, the Atacama Desert is one of the oldest and driest deserts on the planet, covering an area of 105 000 km 2 (150 000 years), and since 150 million years. This desert has a hyperarid core, with climate models predicting major rain events at a derisory pace once in a century. That said, no significant rain has been recorded in this region for 500 years.
But things are changing in the Atacama desert – and not necessarily for the better.
Since 2015, this desert has experienced three important rainy episodes: two in 2015 and one in 2017. The water from these rains was collected in very salty lagoons, which stopped for several months before dissipating. In light of these unprecedented meteorological events, a team of astrobiologists from Cornell University and the Spanish Center for Astrobiology (CAB) visited Atacama to understand how the rains and these hypersaline lagoons may have affected microbial life in this area. exceptionally arid place.
Water can be rare in the Atacama Desert, but that does not mean that the region can not stand life. The soil contains a lot of salt, nitrates and sulphates. Organic compounds, not so much. That said, there is a surprising amount of life in dry soil. Organisms representing the three areas of life (bacteria, archaea and eukaryotes), having evolved over millions of years, have found a place in this area. extraordinary environment.
As the new study shows, recent rains have not been favorable to these tiny critters. Instead of triggering a flourishing life, the rains have devastated the microbial species that inhabit the desert for millennia.
"We show here that the sudden and massive influx of water into regions that have remained hyper-arid for millions of years is detrimental to most microbial surface species, extremely well adapted to survive with meager amounts of water. liquid and perish quickly. osmotic shock when water suddenly becomes abundant, "write the authors.
By "osmotic shock", the researchers refer to a process by which a sudden change in water concentration disrupts the normal functioning of a cell. It's basically a fancy term for cell drowning.
The authors say that unprecedented rainfall results from changing climatic conditions in the Pacific Ocean. A vast "mass of clouds" has arrived in the desert since the Pacific Ocean – an "unprecedented phenomenon," said the researchers, which has occurred twice in three years.
The resulting rainfall has resulted in the widespread extinction of many native microbial species. According to the new study, the local extinction rate has reached 85% in the most affected areas. Extremist organizations, accustomed to arid conditions, were unable to cope with the influx of water.
"The hyperdry soils before the rains were inhabited by up to 16 species of ancient and ancient microbes," said Alberto G. Fairen, an astrobiologist at Cornell and co-author of the new study. "After the rain, only two to four species of microbes were found in the lagoons," said Fairen, also a researcher at the Centro de Astrobiología de Madrid. "The extinction event was huge."
Among the microbes that survived the liquid onslaught was a newly identified bacterium called Halomonas.
This survey shows that the already low microbial biodiversity found in these extreme environments becomes even smaller when water suddenly appears in abundant amounts.
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Researchers say these discoveries could have implications for our understanding of how microbial life could have been extinguished on Mars had it ever happened (something we have not proven yet). Mars is currently a dry and dusty planet, but this is not always the case. In addition, Mars is known to have experienced catastrophic floods in its ancient past.
"March experienced a first period, the Noachian – there are between 4.5 and 3.5 billion years – in which there was a lot of water on its surface," Fairen said.
Finally, the red planet has lost its atmosphere and its surface water has faded. As it happened, however, about 3.5 to 3 billion years ago, large volumes of water were still flowing to the surface.
"If there were still microbial communities resistant to the extreme drying process, they would have been subjected to osmotic stress processes similar to those we studied at Atacama," Fairen explained. "Therefore, our study of Atacama suggests that the recurrence of liquid water on Mars could have contributed to the demise of Martian life, if it existed, instead of representing an opportunity for the microbiota to become resilient. can flourish again. "
It will be interesting to see what will happen in the Atacama Desert. Will our changing climate bring more rain in the desert? And if so, will these rains continue to ravage life or create a new ecosystem? Only time will tell.
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