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  • Wherever there's water on Earth, there's a pretty good chance that you'll find life.

  • Like, even in the driest part of the Atacama Desert in South America,

  • single-celled organisms live in rocks that extract water from the air.

  • And in Japanese hot springs, there are microbes that survive an acidity on par with battery acid.

  • So, in almost any water that would be deadly to you or me, there's probably something that calls it home.

  • But there are a few places full of water that appear to be completely inhospitable to life:

  • some super acidic, super salty, and super hot pools in Ethiopia's Dallol geothermal field.

  • And so far, these pools are the only wet places anyone has found on Earth that don't host life.

  • The Dallol geothermal field is at the top of a volcanic crater filled with salt, and it's a pretty dreadful place to try and live.

  • It's got toxic gases coming out of cracks in the ground, temperatures above the boiling point of pure water, and ridiculously acidic brines.

  • So, these pools aren't exactly jacuzzis.

  • But some scientists who study extremophilesor organisms that live in extreme environmentswondered if anything was possibly alive in there.

  • After all, they'd found a lot of single-cell archaea in nearby areas, including the land around the water,

  • where conditions aren't as extreme, but aren't exactly homey either.

  • So, between 2016 and 2018, an international team of researchers collected 200 water samples from multiple locations in the area to hunt for life.

  • They took water from the steaming-hot, extremely acidic ponds at the top of the Dallol dome,

  • as well as from the nearby Black and Yellow Lakes, which were not as hot or acidic but were super salty.

  • And these samples were completely devoid of any native life.

  • The only signs of life scientists detected were bacteria that appeared to have come from humans or the lab equipment.

  • And there were others that might have blown in on dust carried by the wind.

  • But there was not a single native organism, or any evidence that these foreign cells could actually survive the conditions in the Dallol pools.

  • And there are some pretty good reasons why nothing would want to live there.

  • For one, there's the temperature.

  • The temperatures in these pools range from 40 to 108 degrees Celsius.

  • And when temperatures get too high, molecules that cells need to function, like proteins, start to lose their shape.

  • And if they're the wrong shape, they can't do their jobs.

  • Which is bad, since they're basically involved in every part of keeping cells up and running.

  • And under really extreme temperatures, proteins, and even DNA, will just break down altogether.

  • That's not the only problem in these pools, either.

  • On top of the heat, they're extremely acidic.

  • When acids are dissolved in water, they produce hydrogen ions, which are just plain old protons.

  • And those ions are eager to chemically react with proteins, which, again, messes with a cell's ability to function.

  • So high temperature and acidity are a pretty deadly combination.

  • But to top it all off, these pools are also extremely salty.

  • Living organisms need some salt in their lives, but too much quickly turns deadly.

  • If the concentration of salt in water outside a cell is higher than what's on the inside,

  • water will rush out of the cell to try to balance everything out...

  • and the cell will shrivel up like a raisin.

  • So that's bad to begin with, but certain salty solutions are extra-deadly.

  • Some salt ions, like magnesium, are what's called chaotropic, because they cause chaos.

  • They break hydrogen bonds between water molecules, which can then lead to the breakdown of the complex molecules that organisms need to live and function.

  • In case that's not bad enough, these ions also interact with water molecules in a way

  • that prevents cells from being able to use that water in important chemical reactions.

  • So these ponds are not welcoming to living things.

  • But it's still kind of surprising that there's nothing living there.

  • Because, as deadly as these conditions are, around the planet, there are certain extremophiles

  • that can deal with some of these ridiculous challenges.

  • For example, thermophiles have extra-hardy proteins with extra bonds built in that help them hold their shape.

  • Some of them also have special proteins to repair molecules that have been damaged by heat.

  • And then there are the so-called acidophiles, which are either really good at pumping protons out of their cells,

  • or have special compounds to help keep protons out entirely.

  • And there are halophiles, which have have evolved to tolerate extreme salinity.

  • For example, some of them build up a bunch of potassium ions or other compounds on the inside to balance out extreme salinity on the outside.

  • So there are single-celled organisms that can handle extreme environments.

  • And there's even life that can handle more than one of these deadly conditions at a time.

  • But the Dallol pools seem to be especially deadly.

  • And no one knows exactly why, but there are a few ideas.

  • It may be that its conditions are on the extreme end of extreme.

  • Like, the salinity in the Black and Yellow Lakes is over 50 percent, meaning that the lake is half salt.

  • For comparison, the ocean's salinity is about 3.5%.

  • These lakes also have high concentrations of those chaotropic salts,

  • like magnesium chloride and calcium chloride, that make salty solutions especially deadly.

  • And to make matters worse, there's the one-two punch of extreme salinity and acidity.

  • Scientists aren't sure what, exactly, is so deadly about that combination, but even with so many extremophiles in the world,

  • no one has yet found any organism that can tolerate both high salinity and high acidity, which is what you've got in these pools.

  • Scientists may one day find some other wet part of Earth too extreme to harbor life.

  • Or maybe future tests will find something that can survive these seemingly inhospitable pools.

  • Either way, research like this helps scientists understand what it takes for life as we know it to survive,

  • which can be a good starting point when it comes to looking for life beyond Earth.

  • Thanks for watching this episode of SciShow!

  • And if you want to learn about one extreme place on Earth that does host life, you might like this episode on tiny organisms that live inside solid rock.

  • You can check it out next!

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