Breakdown: Why rain is lethal for this particular desert

Published: Dec. 11, 2022 at 8:24 AM CST
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MEMPHIS, Tenn. (WMC) - Northern Chile is home to the driest desert on Earth: the Atacama Desert.

So dry, in fact, that the only life there is microbial, and NASA researchers study the Atacama to get an idea of what we might find on Mars.

Additionally, NASA uses the Atacama landscape to test rovers and other equipment for Mars missions.

The battery-powered ARADS rover is plugged in for a recharge during field testing in Chile’s...
The battery-powered ARADS rover is plugged in for a recharge during field testing in Chile’s Atacama Desert.(NASA)

Geological evidence suggests the desert has been semi-arid or arid for 15 million years, and no rain had been recorded there for 500 years up until an unusual rain event in March 2015.

A low-pressure system meandered to northern/central Chile from the southwest resulting in one to two inches of rainfall in 24 hours on March 25. A station south of the desert recorded more than 2 inches.

An inch of rain represents multiple years worth of rain for the Atacama Desert.

Scientists thought the desert would bloom with life, but it didn’t.

Instead, the rain killed most microbial life in the region, causing most species to go extinct.

Alberto Fairen, a Cornell University astrobiologist said in a statement: When the rains came to the Atacama, we were hoping for majestic blooms and deserts springing to life. Instead, we learned the contrary, as we found that rain in the hyper-arid core of the Atacama Desert caused a massive extinction of most of the indigenous microbial species there.

The hyperdry soils before the rains were inhabited by up to 16 different, ancient microbe species. After it rained, there were only two to four microbe species found in the lagoons. The extinction event was massive.

Why is water deadly to these microbes?

These microbes had adapted to hyper-arid conditions over millions of years are acclimated to high temperatures, osmotic stress, low nutrients, low water, and UV radiation.

They couldn’t cope with the sudden influx of abundant water into their cell membranes.

And they didn’t go quietly: Up to 87 percent of the bacteria died after having “burst like balloons” from sponging up too much water in their newly aquatic environment.

All this might have significance for finding life on Mars.

More than three and a half billion years ago, geological evidence shows water was abundant on Mars.

Then it became dry, with occasional episodes of massive flooding.

And/ if Martian microbes did resemble their Atacama counterparts, then the washouts probably finished them off, swelling them with water and bursting them like balloons. After a certain point, in other words, Mars might have been too wet to sustain the life that evolved there.

It’s possible, of course, that a few lucky pockets on Mars escaped flooding entirely, allowing microbes there to survive until today.

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