Thanks to Brilliant for supporting this whole week of SciShow.  Go to brilliant.org/scishow to learn more.

(Intro)

The hottest region on Earth is in Eastern Africa, but the heat might be the least interesting thing about it.  It has a volcano featuring one of the planet's few lava lakes, places where molten rock sits exposed full time and it has some of the Earth's hottest, saltiest, and most acidic natural water, but hominids like us humans have lived nearby for millions of years, including one whose skeleton is so famous, I bet you know her name.

Welcome to Ethiopia's Danakil Depression, home to all of the extremes, and to Lucy.  Thanks to its super arid desert climate, the Danakil Depression is so dry that major rivers just dry up there without ever reaching the sea, and the Danakil Depression gets hot.  Death Valley, California might have the hottest verified days on record, but on average over the whole year, Danakil is hotter than anywhere else on Earth, and it's not even like a close contest.

Measurements show that on average, Danakil is about 34 degrees Celsius.  That's a couple degrees hotter than anywhere else on Earth and at least nine degrees hotter than Death Valley, but here, heat doesn't just come from the Sun.  It's called the Danakil Depression because it's lower than everything else around at around 125 meters below sea level.  It's so low because Danakil is the junction of three tectonic plates, the Nubian, the Somalian, and the Arabian, and those plates are spreading apart, leaving the region between them to sink lower and lower, and just like everything else with this area, the Danakil Depression isn't your average plate boundary.  

Underneath Eastern Africa, there's what's known as a mantle plume, a huge mass of magma from within the Earth's mantle is being shoved up against the crust for reasons that scientists don't fully understand.  That plume is helping push those plates apart, and as a result, the Somalian and Nubian plates, which used to be a single plate, will completely split right near Danakil.  This means that the Danakil Depression is one of the few places on Earth where scientists can watch the kinds of processes that might have formed Earth's first plates billions of years ago.

The region experiences lots of earthquakes and hosts its own share of volcanoes, all evidence of the chaos brewing under the crust, and the Danakil Depression's volcanoes work together with its rocks to make the region look pretty different from your classic, monochrome sandy desert.  The hard cracked ground is sometimes surprisingly colorful, where the little water that's available mixes with iron and copper and sulfur from volcanoes and salt from the rocks to produce a rainbow that you would not want to swim in. 

That water is about as acidic as battery acid, ten times as bad as the acid your stomach uses to kill bacteria, and it's heated to around boiling by all that magma beneath the surface, and by the way, the air's not much better.  In some spots, it has so much chlorine in it that it will burn your throat if you don't wear a gas mask, but remarkably, even here, scientists have found a kind of life called extremophiles, microbes adapted to thrive in what we would usually think of as inhospitable environments, and they haven't just found one type of extremophile.  There are at least a couple hardy little organisms there and they're tolerant to so many different extreme conditions that they're not just extremophiles, they are polyextremophiles.  

Now what you won't find in the Danakil Depression today is many larger organisms because it's honestly a pretty unpleasant place, what with the ultra-hot days and the throat corroding air and the pools of boiling acid, although humans do visit sometimes.  In 1974, a team of scientists in the area stumbled upon the partial skeleton of a kind of hominid who used to live there, called Australophithecus afarensis.  That night, they were listening to the Beatles and thought of the perfect name for their discovery: Lucy.  

Hominids include every species related to humans since we've split from the African apes several millions years ago.  Lucy lived a little more than three million years ago and when they found her, she was the oldest, most complete early hominid ever discovered.  Lucy helped us write the story of hominid evolution, helping to answer tons of questions while also inspiring lots of new ones, but despite her fame, we still don't know exactly where she and her closest relatives sit on our family tree, and that's okay.  Scientists can handle uncertainty.  It comes with the job.  

What we do know is that when Lucy was around, the Danakil Depression did not look like it does today.  It's special combination of heat, plate tectonics, elevation, acid, and vulcanism probably only kicked into high gear about a century ago, and it won't last forever either.  Millions of years from now, the African and Arabian plates will have spread far enough apart that the nearby Red Sea will be able to flow right into the Depression they're currently creating, and a brand new ocean will sit where Lucy once climbed trees.

We're just lucky to live right now.  We get to be on Earth when this incredibly weird, unique place exists for us to see and talk about, or if not lucky, like, we're something.  Humans really love knowing about stuff and that's what drive us to study even remote, unforgiving places like this one, to learn more about the world.

And if you like learning more every day, you might be interested in the daily challenges on Brilliant.org.  Every day, they post new challenge questions covering topics like statistics, electricity, and computer science, each one ties into a related course on Brilliant so you can also learn about the topic in depth if it peaks your interest.  These daily challenges are a fun, bite-sized way to learn something new every day, whether you're passing time on the train or just want to make some time for curiosity.  The daily challenges are free for everyone, but premium members get access to the whole archive of challenges and it just so happens that the first 200 people to sign up at Brilliant.org/SciShow will get 20% off the annual premium subscription, so thanks for checking it out.

(Endscreen)