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Hank: There's a bunch of weird places on Earth where biology, chemistry, and geology make it seem like you are on another world.  Here at SciShow, we like to explore lots of these extreme environments and we've collected a few of our favorites in one video for you to enjoy.  We'll start with some caves, which are often home to a bunch of weirdness because they're so isolated from the rest of the planet, and one cave in Mexico was hiding some giant geologic structures.

About fifteen years ago, when a mining company started pumping water out of a cave 300 meters below Naica, Mexico, they were hoping to find lead or zinc or maybe some silver. Once they finished pumping the water out, though, they realized that they weren’t going to be mining anything from this cave – mostly because of the giant, twelve-meter-long spikes everywhere.

The spikes were actually huge crystals, the largest ever found. And the pillars of mineral -- as big as three story buildings -- weren’t the only hazard in the cave. If you managed to make the same descent the miners did, you’d only get to see the crystals for about ten minutes, because that’s roughly how long a human can survive unprotected in the cave.

The appropriately-named Giant Crystal Cave was discovered in 2000, when miners were drilling a tunnel to expand their mine. They’d already pumped the water out of the area, and as they blasted through the rock, they revealed the thirty-by-ten meter cave, containing enormous crystals of selenite -- a crystal form of the mineral gypsum.

The conditions in the caves are a collection of extremes. The thermometer reads about 58 degrees Celsius on a good day, and the humidity hovers around 100 percent. The cave contains hundreds of crystals, some up to twelve meters long and weighing about 50 metric tons. It’s so hot and humid in the Giant Crystal Cave that the insides of your lungs would actually be the coolest surface around. So the water vapor in the air would condense in your lungs as you breathed, and that is not a great thing to have happen to you. Essentially, if you stayed in the cave long enough, you’d drown in your own lungs.

So, understandably, these conditions make scientific research kinda tough. Scientists have to go in there with custom-made, super-powerful refrigeration suits, but even those only buy them about half an hour at a time. So we still have a lot to learn about the cave and what’s in it -- maybe even forms of life we've never seen before. It might seem unlucky that the cave with the largest crystals in the world is so inhospitable, but those conditions are actually the perfect nursery for these mineral formations.

The cave lies deep beneath Naica mountain, which formed about 26 million years ago from volcanic activity. And all of that molten lava came with a bonus: a whole lot of anhydrite. Anhydrite is the dehydrated form of the mineral gypsum -- both compounds have the same chemical makeup, except for the anhydrite is missing water. But if conditions are right, anhydrite can absorb water and become gypsum. And if the anhydrite turns into gypsum slowly enough, it will crystallize, to form selenite -- just one of the many forms that gypsum can take.

The real key to this process is temperature. If it's above 58 degrees, anhydrite will be stable, and just sit there. But at or below 58 degrees, it’ll begin to dissolve, and use the water in the environment to essentially re-form into gypsum. And that is exactly what happened in Giant Crystal Cave. Once the magma beneath the mountain cooled to around 58 degrees, the anhydrite began dissolving very, very slowly. Then, new particles of the hydrated gypsum began to form as crystals of selenite.

Now, other caves in this same mountain -- like the one with the particularly boss name of Cave of Swords -- also contain lots of selenite crystals. But the crystals there are only about a meter long, because that cave cooled more rapidly, so the hydrated gypsum formed too quickly to deposit as very large crystals. But Giant Crystal Cave was just deep enough in the ground to stay at the transition temperature. Since the cave was around 58 degrees for about a half a million years and filled with anhydrite-rich water, the selenite crystals just kept on growing until the year 2000, when we pumped the water out. Technically, there’s no limit to how big the crystals can get in such perfect conditions. So, when the mine eventually closes and we stop pumping the water out of the cave, the crystals will again start growing.

So huge crystals are cool, but caves are also home to plenty of other things, too.  Like, there's a cave in Romania that was sealed off from the rest of the world for millions of years, leading to some really weird forms of life.

Weird stuff happens in caves. Venture into the darkness and you never know what you might find: glow worms, crystals, millions of sleeping bats, a Horcrux, Grendel's mom...

In 1986, a prospecting crew in southern Romania was looking for a good place to build a geothermal power plant, when they accidentally discovered one of the oddest caves of all. It's called Movile cave, and it's basically a time capsule, crawling with strange life that has lived separate from the rest of Earth for millions of years.

More than 20 meters underground, the cave is pitch dark, warm, and full of toxic gases, and holds a lake that reeks of burnt rubber and rotten eggs. And other than the prospecting shaft, the cave is totally sealed up in all directions. You heard me right, it's been cut off from the rest of the world for about five and a half million years, making it one of the most isolated places on Earth.

Thanks to the thick layers of clay above the cave, nothing seeps down from the Earth's surface: no sunlight, no food, and no water. There aren't even any traces of radioactive metals from the Chernobyl nuclear accident, which are spread throughout the soils and lakes near the cave. But there are all sorts of hardcore creepy crawlies down there, and they've formed a complex ecosystem.

Movile's lake water is covered by a tissue paper-like mat made up of billions of autotrophic bacteria, which can turn inorganic compounds like carbon dioxide, along with some energy, into food. And the air in the cave has about 100 times more carbon dioxide than outside air, which provides them all the CO2 they need.

Here on Earth's surface, lots of organisms, like plants, use light and carbon dioxide to make food. That's photosynthesis. But these bacteria cannot use photosynthesis, they live in total darkness, so they don't have access to sunlight or any light energy at all. So instead they use chemosynthesis, or energy from chemical reactions involving the toxic gases in the cave, like hydrogen sulfide, to help generate their food.

Other kinds of bacteria floating in the lake use methane gas as their only source of carbon and energy. Worms, shrimp, and other smaller organisms feast on all of these microbes, and then larger invertebrates, like spiders and centipedes, feed on them.

Not only do these chemosynthetic bacteria support an entire ecosystem, but they also end up shaping the cave itself. Reactions involving hydrogen sulfide gas produce sulfuric acid, which erodes the limestone walls over time. That gradually makes the cave bigger and also releases more carbon dioxide gas. It's a pretty cool ecosystem and the Movile Cave is the only place we know like this.

At least, on land. Deep down in the ocean there are geothermal vents thick with the same types of toxic gases found in the cave, and there are similar chemosynthetic bacteria living around those vents. Both Movile Cave and the vents might resemble the dark and gassy conditions of the early days of planet Earth, which has left some scientists wondering if these Movile microbes might be similar to the first kinds of life.

But even though similar bacteria have been found elsewhere, what about all those larger invertebrates? To be honest, they're a bunch of creepy looking weirdos, but I guess living in total isolation and darkness for millions of years will do that to you. Scientists have discovered 48 species in the cave, 33 of which were previously unknown, including three spiders, a leech, a centipede and a very unusual insect called a water scorpion that actually seems to be related to bed bugs.

These organisms show the troglomorphic adaptations that are associated with life in the dark, like lack of skin pigmentation, and extra long antennae to help them feel around in the darkness. In fact many are born without eyes at all, since they don't have much use for them.

By now though you might be wondering how the heck these creatures got stuck underground in the first place. Well, we're not entirely sure. One hypothesis is that the changing climate at the end of the Miocene five and a half million years ago may have had something to do with it. Colder, drier conditions on the Earth's surface could have sent surface invertebrates underground, looking for shelter and warmth. And when the cave eventually sealed up, they were trapped.

One of Movile's spiders is closely related to a surface species found four thousand kilometers away in the Canary Islands which may support this theory. Then again, it's also possible that some critters just fell in through cracks in the limestone more recently, like two million years ago instead of five. Either way it's a fascinating look at the strange ecosystems that can form in extreme places.

And now it's time to leave these cramped, dark caves and think way bigger, because there's a weird place that can only really be appreciated from space.

It's been less than a hundred years since we got our first really good look at the geological marvel known as the Eye of the Sahara, despite the fact that people have been walking across it right there in the middle of Mauritania for thousands of years. But at 50km across, it helps to have a wider view of one of the world's coolest geological features.

So the best way to see the formation, formally known as the Richat structure, is from space. It's so big that early NASA missions actually used it as a landmark. Given the structure's concentric circles and uncanny symmetry, it's hard to fault scientists for initially suspecting that it was a crater from some enormous impact. But it is not the product of a meteor, comet, or even an ancient volcano as scientists once theorized.

While there's still disagreement about how this almost perfectly circular shape came to be, most scientists will tell you that the Richat structure is actually a deeply eroded geologic dome. This dome formed more than 100 million years ago when the churning landmasses that make up Africa caused the lithosphere, that's the crust and the upper mantle of the earth's surface, to weaken.

This weakness allowed the dome to rise up as magma swelled below the surface. Geologists call this kind of uplift an anticline, basically an enormous fold of rock sticking up from its surroundings. And this one was nearly symmetrical, a circular anticline.

The fold contained alternating layers of the three most common types of rocks, sedimentary, metamorphic, and igneous. And because of how an anticline forms, the oldest rocks in the formation are at the center of the fold while the younger rocks are on the outer layers. Over millions of years the dome eroded away, likely sped along by all the hydrothermal water in the area, another symptom of the magma lurking near the surface.

The different types of rocks erode at much different rates, so the layers of sedimentary rock, which erode more easily, were worn away to form the valleys within the structure. Meanwhile, the harder metamorphic rocks, like quartzite, and igneous rocks, which are more resistant to erosion, remained. This left the oldest rocks exposed as cliffs separated by valleys where the younger, softer rock used to be, creating the Richat structure's weird concentric landscape.

So, if you're ever in Mauritania or at low Earth orbit, keep a big ol' eye out for it.

It sort of feels like the Earth has a giant eye of Sauron just like, looking for planets with rings, and if that's not spooky enough for you, here's a spot in Antarctica where it looks like the Earth is bleeding.

Blood Falls! Not only has one of the awesomest names of any location on Earth, I mean we were trying to come up with a good joke to tell, it turns out there's actually a Vampire Diaries fan-site call blood falls. So it turns out we didn't even have to write a joke, it was already existing in real life. But Blood Falls, in addition to being a Vampire Diaries fan-site, is also probably the southernmost of the weird places that you might visit in your lifetime. If you happen to ever visit Antarctica.

You've heard me go on before about Antarctica's sub-surface lakes. I go on about them because they're really nard-rockingly amazing, rivaled only by the deep ocean floor as the unlikeliest places on Earth where scientists keep finding strange new living things.

In early 2013, for instance, scientists reached the ancient underground Lake Whillans in West Antarctica and found microbes under 800 meters of ice, about 5,000 bacteria in every teaspoon of water, where temperatures can reach -5 degrees Celsius and no substance has ever known the case of sunlight.

At Blood Falls, it's even stranger, and cooler to watch.

Here in a valley in East Antarctica water periodically emerges from the sub-glacial lake 400 meters underground. And the water is not only super salty, almost three times saltier than seawater, it's also incredibly old and it can run as red as a vampire's eyes.

The story of Blood Falls begins around 5 million years ago when East Antarctica was inundated by the sea, forming a salty lake. Some 3 million years later, glaciers began to form and moved over it, isolating the lake and its inhabitants from the rest of the world in a biological time capsule.

As the salt water on top slowly froze, it made the remaining water underneath saltier and saltier, so much so that today, even though it's now well below zero degrees Celsius down there, the water won't freeze! And in addition to being wicked cold and hecka salty, the water is also chock full of iron scraped up from the glacier by the bedrock below.

There's almost no free oxygen floating around under the ice, but when the iron-rich water reaches the surface, oxygen in the air turns the iron into rust, and not just a tawny brown rust but a rich, red, sanguine rust that gives the falls its name.

So it's a site to put on your bucket list for sure, but I gotta say the most amazing feature of Blood Falls is what's been found living there.

For 2 million years, in a salty liquid habitat that probably tastes like roofing nails with no light or breathable oxygen, a community of microbes has found a way to survive that scientists say has never been observed elsewhere, by using iron to breathe, kinda.

The bacteria actually seem to get their energy from sulfur, much like those found at deep sea thermal vents, which they're probably related to. At Blood Falls, they respire by breaking apart oxygen-containing sulfur compounds called sulfates, but then the leftovers of this reaction interact with the iron in the water to restore those sulfates, essentially recycling the organisms' sole energy source.

Pretty slick, right?

The fact that organisms can survive like this has all kinds of implications for understanding the capacity for life, not only on other worlds, but also in Earth's distant history.

Like during the so-called snowball Earth period when much of the planet was thought to have been covered in ice some 700 million ago.

So, Blood Falls. The next time you visit Antarctica you should totally go there.  

Well, I am probably not going to go there.  Besides Antarctica being frickin' cold, it's a little too windy for my tastes, but that brings us to our next weird place, which is probably caused by extreme winds.

The Dancing Forest of Kaliningrad is exactly the kind of place where you'd expect to find a werewolf creeping through the mist. Located in a place called the Curonian Spit off the Baltic Sea, on the border of Russia and Lithuania, the strange forest is known to locals by a jollier name, the Drunken Forest. Because, well, the stand of pine trees looks more than a little schnockered as they twist and curve, stretching upward in contorted loops to find their way to the sky. And here's the thing -- no one knows why these trees look like they're grinding to Marvin Gaye.

Of course theories abound, some suggesting unstable soil is the cause, or beetle damage, or even nuclear radiation. Local legends say the crawling through one of these tree loops in the right direction will earn you an extra year of life. A more popular, non-magical theory suggests powerful winds were the original shaping force. And there is a precedent for that - if you've ever hiked into an alpine zone forest, you've probably seen patches of stunted, twisted, super cool, mini trees called Krummholz. They get to thoroughly clobbered by harsh, cold winds that they end up growing more horizontal than vertical.

But, some people think that the trees in the Dancing Forest have been trained to grow that way. Humans have long been manipulating trees for commercial or aesthetic purposes. Mr. Miyagi and his bonsais - he was all about tree-shaping. Humans can train a young tree to grow in unconventional ways by laying a heavy object on its skinny trunk, sometimes for years. The tree, just like the houseplant on your windowsill, wants to grow toward the sun really bad, and no weight is going to stop it from reaching the light, a process called phototropism. And whether plants are made to bend intentionally or not, the effects of phototropism can change the character of its tissues.

In trees, the wood that forms under the pressure of weight is called reaction wood, or in conifers, compression wood. It's created when the layer beneath the tissue is bark called the Cambium thickens the source of the pressure to support the horizontal weight of the tree. In time, the funny shape of the bend becomes permanent and it leaves behind a record of oval or oblong instead of more circular rings.

In the case of the Dancing Forest, local historians have no recollection of any human manipulation to create this effect but there is another forest in North West Poland called the Crooked Forest made of about 400 Pine Trees that all have uniform 90 degree bends at the base of their trunks. The trees are all the same age and they all bend North - because of this uniformity many people believe that this forest was manipulated by humans perhaps to grow uniquely shaped wood for oxen yokes, ship hulls or for furniture making. That particular theory maintains that the trees were shaped before 1930 but were abandoned before they could be harvested with the outbreak of World War II. But ultimately even the cause of the Crooked Forest's odd tree shapes remains a mystery and they could also be attributed to some powerful force like strong winds, heavy snow and ice pack or even the result of one of my favorite theories - being run over by Nazi tanks as young trees during the war.

Now all this reminds us that while Scientific explanations of natural phenomenon are usually pretty cool and often necessary, sometimes it may be cooler for it just to be a mystery.

And now that we've covered extreme rocks, life forms, water, and trees, what would be a weird places compilation without at least one volcano?  So to wrap things up, we've got a video about an Indonesian crater where the lava appears to glow blue.

Olivia: While scrolling through social media, you might have seen some pictures of bright blue lava flows and raised a skeptical eyebrow And hey! Good for you doubting stuff on the internet because Photoshop is a thing. But those photos are real.

Even though the molten rock isn't what's blue. It's actually combusting gases that make the glowing blue flames. A volcanic crater on the island of Java in Indonesia called Kawah Ijen is the best place to see this phenomenon at night. Plus, the crater also has a deadly vivid turquoise lake which is full of acid.

The chemistry of the volcano causes both of these brilliant colors, but in two different ways. Lots of volcanoes spit up gaseous sulfur compounds. Like the Dallol Volcano in Ethiopia, so blue flames aren't unique to this crater.

But Kawah Ijen happens to have spectacular amounts of sulfur, enough to support a huge mine. The miners are after the bright yellow chunks of solidified sulfur rock. But its sulfur forms a yellow solid, why do the sulfuric gases seeping up from the ground burn blue?

It all has to do with the chemistry of combustion. When a fuel like a sulfur compound mixes with oxygen and high enough temperatures, a combustion reaction happens. Heat gets released and new chemicals are formed, like sulfur dioxide, and the visible part of the fire is the flames which are caused by a bunch of atoms spewing out light energy.

Basically, the energy from the combustion reaction boosts the electrons in the fuel atoms to a more energetic state. When the electrons fall back to their original state, they release all that extra energy as a photon of light. The wavelengths of those photons determine what the flame's color is. And in the case of sulfur compounds catching fire, it's an eerie blue glow.

During the day, Kawah Ijen's lava looks pretty much like the orangey-red lava of any active volcano. All the sulfuric gases are still burning, but the bright sunlight washes the color out. But at night, sightseers flock to see all of the glowing blue flames on the rivers of molten rock. If that wasn't enough to make Kawah Ijen one of the world's weirdest places, then there's also that turquoise acid lake.

Volcanoes tend to bring all sorts of chemicals from the Earth's interior up to the surface. And in Kawah Ijen's case, there are plenty of things besides sulfur like chlorine and a bunch of metals. In the crater lake water, the sulfur dioxide gas made by the combustion reaction dissolves and forms sulfuric acid. And the chlorine compounds mean that there's hydrochloric acid in there too. The pH of that crater lake is, no joke, below 0.5. Which is really really acidic, like stronger than the acid in your car battery.

Needless to say: don't go swimming in that death lake, no matter how cool it looks. Even just measuring the pH of the water can be a really dangerous job. Acid that strong can dissolve metals no problem, and dissolved metals do something that organic carbon containing chemicals usually don't: they turn bright colors. The color you get and whether you get a color it all has to do with the chemistry and geometry of the metal ions floating inside the solution.

Many kinds of metal ions absorb certain wavelengths of visible light, and your eyes perceive color based on the wavelengths of light that are reflected off an object, so when a metal ion absorbs one color of visible light, you'll usually see a complementary color to the one that's absorbed, the hue that's across from it on the color wheel. If a compound absorbs light outside of the visible spectrum, all of the visible light gets reflected and the solution looks white or clear.

That's why organic chemistry might as well be called "six hundred colorless compounds and how to draw them." Inorganic chemistry is where all the colors are, so, the mixture of dissolved metals in Kawah Ijen's lake is what makes the water look vividly turquoise. If the volcano were to erupt, there's a chance that the lakebed could rupture and send that acidic "death water" cascading down the mountain to do serious harm. And because Java is so densely populated, volcanologists keep a very very close eye on any volcanic activity in the area.

So Kawah Ijen owes its incredible colors to sulfur compounds. Whether they're burning or dissolved in the lake with some metals. Those two different kinds of chemistry make this weird place a beautiful and deadly destination.

Hank: Thanks for joining us for this compilation of some of the weirdest places on wonderful planet.  If you want to keep learning about strange science with us, just go to YouTube.com/SciShow and subscribe.

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