Rain episodes have been recorded for the first time in the hyperarid heart of the Atacama Desert and, surprisingly, the sudden abundance of water was devastating for the existing microbial life.
The Atacama Desert, the driest and oldest on Earth, is located in northern Chile and has a hyperarid heart in which at least 500 years ago there have been no rains. But this has changed in the last three years. Rain episodes have been recorded for the first time in the hyperarid heart and, surprisingly, the sudden abundance of water was devastating for the existing microbial life. This is the conclusion of a recent study, published in Nature Scientific Reports,, by an international group of researchers from the Spanish Centro de Astrobiología (CAB, CSIC-INTA). For scientists, these unexpected rains are attributed to global climate change.
"Our group has discovered that, contrary to what would be intuitively expected, the presence of water has not meant a flourishing of life in the Atacama, but on the contrary, the rains have caused a huge devastation in the present microbial species before rainfall", explains Armando Azúa-Bustos, researcher at CAB and first author of the study.
"Our study shows that high rainfall has caused the mass extinction of most indigenous microbial species. The extinction range reaches 85%, 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 low environmental humidity, have been unable to adapt to the sudden flooding, dying under the new water excess conditions", adds Azúa-Bustos.
FROM ATACAMA TO MARS
This study represents a breakthrough in understanding the microbiology of extremely arid environments. It also presents a new paradigm to understand the evolutionary route of the hypothetical early Martian microbiota, because of Mars is an hyperarid planet that 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", says Alberto G. Fairén, researcher at CAB and co-author of the study. "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", explains Fairén.
Then Mars lost its atmosphere and hydrosphere and became the dry and arid world we know today. "But during the Hesperian period (from 3.5 to 3 billion years), large volumes of water dug their surface and form overflow channels, the largest in the Solar System. If there were still microbial communities living under extreme desiccation conditions, they would have been undergone osmotic stress processes similar to those observed in Atacama", explains Fairén.
"Therefore, the Atacama study suggests that the recurrence of liquid water on Mars may have contributed to the extinction of Martian life, if it ever existed, rather than became an opportunity for the re-flowering of resilient microbiota", concludes the coauthor of the study.
In addition, this new study notes that large deposits of nitrates at the Atacama Desert offer evidence of long periods of extreme dryness in the past. The nitrates were concentrated at valley bottoms and former lakes by sporadic rains about 13 million years ago, and can be food for microbes. The Atacama nitrates may represent a convincing analog to the nitrate deposits recently discovered on Mars by the rover Curiosity (and reported in a 2015 study entitled "Evidence for indigenous martian nitrogen in solid samples from the Curiosity rover investigations at Gale crater", in the Proceedings of the National Academy of Sciences). Earlier this year, Fairén and colleagues discovered that short-term wetter environments in early Mars, occurring sporadically in a generally hyperdry early planet, explains the observed martian mineralogy. This study, entitled "Surface clay formation during short-term warmer and wetter conditions on a largely cold ancient Mars", was published in February in Nature Astronomy. "These long periods of dryness, followed by short-term wetter conditions, may also be in the origin of the nitrate deposits on Mars", concludes Fairén.
Referencia bibliográfica:
A. Azua-Bustos et al. 2018. Unprecedented rains decimate surface microbial communities in the hyperarid core of the Atacama Desert. Scientific Reports. DOI: 10.1038/s41598-018-35051-w
