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By NASA // July 31, 2018
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The Atacama Desert is one of Earth's environments that is closest to the desiccated Martian surface
Researchers collect samples of the desert surface of Atacama at Chile, a few centimeters in the ground. (NASA Image)
(NASA) – Life as we know it needs water to thrive. Even so, we see life persisting in the driest environments on Earth. But how dry too ? How much is an environment too extreme for even the smallest and most resistant microorganisms to survive?
These questions are important for scientists seeking life beyond the Earth.
To answer this question, a team of researchers from NASA's Ames Research Center in California's Silicon Valley went to the driest desert on the planet: the Atacama Desert. in Chile, a 1,000-kilometer strip on the west coast of South America. Earth's environments that come closest to the deserted Martian surface. But Atacama is not uniformly dry.
Passing from the southern end of the relatively less dry desert of central Chile to its extremely dry center in northern Chile, annual precipitation drops from a few millimeters of rain a year to just a few millimeters of rain per decade
This non-uniformly dry environment provides an opportunity to search for life at decreasing precipitation levels. By fixing the amount of water an environment needs to be livable, that is, capable of supporting life forms, the research team was able to determine that it existed a dry habitability
"On Earth we find evidence of microbial life everywhere." said Mary Beth Wilhelm, an astrobiologist at Ames and lead author of the new study published in the journal Astrobiology this month -this. "However, in extreme environments, it's important to know if a microbe is dormant and barely surviving, or really alive."
Biologists define something as living if it is capable of growth and reproduction. If microbes simply survive or perform a few basic functions, they will die in a generation without transmitting any genetic information.
When they look for the potential of life on Mars, scientists must see this reproduction occur, which leads "By learning if and how microbes stay alive in the extremely dry regions of the Earth, we hope better understand if Mars has ever had a microbial life and if it has survived until the end of life, today, "Wilhelm said.
The Atacama Desert is one of the Earth's environments that comes closest to the desiccated Martian surface. But Atacama is not uniformly dry. (Image from NASA)
A sign of stress is a sign of life
Scientists have some tools to determine whether a sample is growing or just surviving. An important sign is stress. Living long enough to grow and adapt in extreme deserts like Atacama – or potentially on Mars – is not an easy task.
If life really develops in this extremely dry environment, it will be emphasized, while the dormant life will simply survive. do not. Because the dormant life is not even able to grow or reproduce, there are no stress markers, such as changes in the structure of certain cell molecules. Astrobiologists can look for telltale signs of this stress to look for signs of growth in dry soils.
The scientific team took soil samples from the Atacama Desert and brought them back to their laboratory in Ames. There, they performed tests to identify stress markers in the samples by looking at features common to all known living organisms.
A stress marker can be found in lipids, molecules that make up the outer surface of a living microbial cell. its membrane. When cells are exposed to stressful conditions, their lipids change their structure, becoming more rigid.
Scientists have found this marker in less dry regions of Atacama, but mysteriously absent from the drier areas where microbes should be more stressed. 19659009] Based on these findings and others, the team believes that there is a transition line between minute amounts of water for life and an environment so dry that the Microorganisms simply survive without growth of surface soils in Atacama. Dating the Remains of Life
Scientists can tell how long cells have died by studying a type of molecule called amino acids, the building blocks of proteins. The structures of these amino acids take two forms, each mirroring the mirror of the other, like a pair of hands. In fact, this "hold" is the term used by scientists to describe these structures.
All life on Earth is built with "left" amino acid molecules. However, when a cell dies, some of its amino acids evolve at a known rate toward the "right-handed" reflective structure, eventually balancing in a 50-50 ratio over several years
. In the soils of Atacama, scientists found dead microbes for at least 10,000 years. Finding even the remains of life this ancient is extremely rare, and surprising for a sample sitting on the surface of the Earth.
Preparing for Mars
Mars is 1000 times drier than the driest parts of Atacama, which makes it less likely that microbial life as we know it exists at the surface of the planet even with access to water.
However, even in the drier areas of the Chilean desert The times of Atacama's history were clearly present and well preserved for thousands of years
This means that scientists know that Mars was a wetter and more vibrant planet in the past, but traces of this ancient life could be intact. "Before we go on Mars, we can use Atacama as a natural laboratory and, based on our findings, adjust our expectations for what we might find when we get there," Wilhelm said.
"Knowing the surface of Mars today could be too dry for life to grow, but traces of microbes can last for thousands of years, helping us design better instruments not just for seek life on and under the surface of the planet, but also to unlock the secrets of its distant past CLICK HERE TO SEE THE WIDE OF THE COUNTY OF BREVARD
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