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Washington, DC, July 25 (IBNS): Life as we know it needs water to thrive. Even so, we see life persisting in the driest environments on Earth. But to what extent is an environment too extreme for even the smallest and most resistant micro-organisms to survive?
These questions are important for scientists seeking life beyond the Earth. To help answer this question, a team of researchers from NASA's Ames Research Center in Silicon Valley, California traveled to the driest spot on the planet: the Atacama Desert in Chile , a 1000 km strip
The Atacama Desert is one of the closest terrestrial environments to the desiccated Martian surface. But Atacama is not uniformly dry.
Traveling 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 , read the NASA website.
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 limit of habitability.
"On Earth, we find everywhere evidence of microbial life. said Mary Beth Wilhelm, an astrobiologist at Ames and lead author of the new study published in the journal Astrobiology this month. "However, in extreme environments, it's important to know if a microbe is dormant and barely survives. , or really alive. "
Biologists define something as living if it is capable of growth and reproduction If microbes simply survive or perform some basic functions, they will die in a generation without transmitting any When they search for the potential of life on Mars, scientists need to see this breeding, which leads to population growth and genetic change from one generation to the next. 19659002] "When we learn if and how microbes stay alive in the extremely dry regions on Earth, we hope to better understand if Mars has ever had a microbial life and if It could have survived until today, "Wilhelm said.
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. 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 at Ames. There, they performed tests to identify stress markers in the samples by examining 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, known as the membrane. When cells are exposed to stressful conditions, their lipids change their structure, becoming more rigid.
Scientists have found this marker in the less dry regions of Atacama, but mysteriously absent from the drier areas where microbes should be more stressed. Based on these findings and others, the team believes that there is a transition line between minute amounts of water for life and a dry environment that micro-organisms organisms simply survive without growth of the surface of Atacama. 19659003] 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 "outstretched hand" 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, making it less likely that microbial life as we know it exists on the surface of the planet, even with some access to water. However, even in the drier areas of the Chilean desert, remnants of microbial life from Atacama's more humid past had been clearly present and well preserved for thousands of years. This means that because scientists know that Mars was a wetter and more alive planet in its past, the traces of this ancient life could still 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 to not only look for life on and under the surface of the planet the secrets of its distant past. "
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