The Only Water on Earth Without Life


♪♪♪ 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 extremophiles—or
organisms that live in extreme environments—wondered 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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