MICHAEL: The ocean is an incredibly mysterious place which is part of the why we've done so many Sci Show episodes about it. But the ocean isn't just fascinating because cool things live there, there are also ghostly towers, mountain ranges longer than continents, and all kinds of other features you wouldn't expect under the water. So, let's dive in. 

First, when you think of the ocean, snow probably isn't what comes to mind. But arguably the most amazing snowfall on earth happens deep underwater, it's just not the kind of snow you're thinking about. Here's hank with more. 

HANK: If you're taking a trip to the deep ocean, you should know the forecast. It's going to be cold and dark with a high chance of snow. Okay, well, not snow as in ice crystals like up here on the surface of the planet, we're talking about marine snow. It looks like snow. It is not. It's comprised of fluffy buts of organic matter that range in size from about half a millimeter to several centimeters across. And this snow isn't just pretty, it's an essential part of our ocean food webs and our global climate. 

Now, organic matter can refer to pretty much anything that is or was alive, but in this case, we're generally talking bout the remains of plankton. Plankton is a catch-all term for the organisms that are largely at the mercy of water current. And they're often tiny, things like algae, bacteria, protozoans, little crustaceans like krill, and even the early life stages of much larger animals.

When these creatures die, what's left of their bodies starts to sink, becoming part of marine snow. Not all these snow particles are part of dead plankton though, some are fecal pellets. It's gotta go somewhere. Marine snow also contains decomposers like bacteria that attach themselves to the falling poo in tiny carcasses

and as the different bits descend, they clump together to form larger and larger flakes, which eventually give the appearance of a blizzard far below the waves. 

And this snowfall brings something very important to deeper waters: food. See, in the shallow ocean where sunlight beams through the water, plankton that can photosynthesize are the base of the food web, just like the plants that are the base of the food web up on land. 

And in some places in the deep ocean, there are nutrient-rich areas like hydrothermal vents which provide food for special bacteria that can form the base of their own ecosystems. Instead of using light for energy, these bacteria turn carbon dioxide into sugars by tinkering with chemicals like hydrogen sulfide, a process called chemosynthesis.

But most of the deep seafloor doesn't have these vents, and in the water column below about a thousand meters, there is no sunlight, so locally produced food is very scarce. And yet, life persists because what they need drifts down from above. Many animals eat the falling particles as they drift down through the water column like this larvacean.

The animal itself is just a small tadpole-like thing in the middle, the rest is the giant mucous net it constructs to catch and concentrate the descending organic matter. Over time though, the net clogs, so the larvacean tosses it and makes a new one. Of course in the deep, nothing goes to waste, and Mbari researchers have found that the mucous snowballs are an important source of food for other animals, like this vampire squid.
And at the seafloor, other filter feeders and scavengers scoop up even more of the falling snow. Even with all these hungry mouths though, some of the snow sticks. The particles that don't get eaten settle on the bottom and as they decompose, they form a nutrient-rich top soil-like ooze that coats much of the vast seafloor. This is all part of one of the most important 

biogeochemical processes on the planet, the carbon cycle which is key to understanding climate change.

As far as we know, all life on earth needs carbon. It's a key component in essential molecules like DNA and RNA and the fats that make up our cell membranes.

So the distribution of carbon in different environments can influence what lives there, like without the carbon and other nutrients that sink from the shallows, most deep-sea organisms wouldn't exist. But this snow doesn't just impact life in the deep by playing a role in the carbon cycle, it affects all life on earth, including us. That's because the carbon these plankton have in their bodies had to enter the seawater from somewhere.

That somewhere is generally the atmosphere because it falls with the rain or it directly diffuses into the water. Once in seawater, carbon can be used by organisms to build their bodies and shells. Then when those organisms are digested by predators or decomposers, the carbon can be released as carbon dioxide.

If this happens in the shallows, it can diffuse back into the atmosphere. But marine snow pulls carbon from this water to air cycle and tucks it away in oozes on the seafloor. In places that this ooze builds up, it's gradually been pressed into huge deposits of chalk and other forms of limestone.

These rocks now cover roughly 3 billion square kilometers of the seafloor. In some spots, they're hundreds of meters thick.  In fact, these carbon-loaded rocks are the earth's biggest carbon storage unit. The carbon can eventually return to the surface.

Techtonic activity can push these ocean rocks beneath continents, where they may melt, rise upwards, and fuel volcanoes that pump CO2 into the atmosphere when they erupt. but that takes many millions of years. Until then the carbon is essentially locked away. Over time, marine snow has been storing more and more carbon into the depths.

According to a 2019 modeling study, around 80 million years ago, during the cretaceous period when dinosaurs like velociraptors roamed the land, about 1 million tons of carbon in the form of carbonate were stores each year in deep-sea sediments. But today, scientists estimate over 200 million are stored annually. 

And all the carbon in the deep because of marine snow may have paved the way for our current, comfortable climate. See, over that same time period, our planet cooled dramatically, shifting from the warmer hothouse of the cretaceous period to our current ice house conditions where we have permanent ice caps widespread grasslands, and a cooler climate. 

That's because carbon dioxide in the atmosphere acts as a greenhouse gas, one that absorbs and traps heat. So though there are other things involved, in general, the less co2 we have in the atmosphere the cooler our planet is. 

And when more of the planet's carbon is in rocks, there's less in the atmosphere. Of course, these days we've been reversing all of that carbon storage. We're essentially doing what takes volcanoes millions of years in a geological instant by burning fossil fuels and cutting down forests. And because of our actions, we're causing the co2 level in our atmosphere to rise and fundamentally changing our climate. 

That's what scientists are so eager to understand how our activity affects marine snow. It will give them a better sense of how the planet will change in the years, decades, and centuries to come. We do not want to go back to the hothouse of the cretaceous. So in addition to taking some steps to reduce admissions, we want marine snow to keep pulling carbon down into the depths. 

Right now, our ocean is doing us a very big favor, thanks in part to Mbari's crew of robotic floats, we know that it soaks up a quarter of the excess carbon dioxide we pump into the atmosphere and more than 90% of the planet's excess heat. But as atmospheric CO2 levels rise, more carbon dioxide enters the ocean, and that makes the water more acidic

which can disrupt the formation of carbon storing oozes. That acidity is also messing with plankton communities, which could ultimately affect how much carbon makes it down to the ocean floor. So scientists are keeping a close eye on marine snow and how it is or isn't changing in response to our actions. Because if current trends continue, we're gonna need all the carbon storing help we can get.

If you were to follow that marine snow down toward the ocean floor, you wouldn't find a flat featureless landscape. Instead, you might come across a mountain range. There is one sitting right in the middle of the Atlantic Ocean, pointing to a process affecting literally the entire planet. And we know about it thanks to a researcher named Marie Tharp. Here's another one from Hank.

Despite having sailed over it for thousands of years now, we still know shockingly little about the seafloor. Like as of 2017, only 6% of the ocean floor had been mapped in detail. But one thing we do know is that the ocean floor is not a flat featureless landscape. Just like the world above the water, it's full of valleys, canyons, mountains, and plains.

It is also home to some of the biggest events shaping our planet. And we would know a whole lot less about all of that without the work of a researcher named Marie Tharp who successfully changed our understanding of the ocean and also the entire world.

Tharp's story began in 1948 when she was employed at what's now the Lamont-Doherty Earth Observatory in New York. At the time her job was to do drafting and computing for graduate students, one of whom was Brian Hazeen.

Before Tharp joined the group, Hazeen had collected extensive data about the floor of the Atlantic Ocean. But since he was often away at sea and because regulations didn't allow women to sail on research vessels, Tharp took over the task of organizing his data. Before long she was working on Hazeen's project exclusively and that turned out to be huge for the future of science.

See, Heezen was involved in collecting sonar data from ships which was used to measure the ocean's depth and while sonar is common today, this was like, cutting edge work at the time. In the past, depth measurements were made with sounding. That's where researchers would lower a rope with a weight on the end over the side of the ship, and then when the weight hit the bottom, someone would mark the depth, and then they'd pull up the rope. I guess that's how you'd do it. 

There were, of course though, some problems with this, Like sounding, was often inaccurate because the weight would rarely fall straight down, Also that gives you one data point at a time, which means it was exhausting to map a big area. So the advent of sonar drastically improved things. Instead of a rope, the ship would produce sound waves and measure the amount of time it took for the waves to bounce off the seafloor and return to the ship. Then, because we know the speed of sound and water, researchers could calculate the depth of the ocean with some quick math. Thanks to sonar, Hazeen had compiled tons of data, but Tharp figured out what to do with it.

She made hand-drawn diagrams that plotted the ships' paths and their depth measurements. Then, by stitching them together, she created what were basically topographical maps of the seafloor, and as she did, she found something unexpected. A cleft in the center of the North Atlantic ocean, kilometers wide and hundreds of meters deep. She thought this looked a lot like a rift valley, a feature first observed on land that forms when two tectonic plates pull apart from each other. Tectonic plates being the giant slabs that make up the eath's surface. Except at the time, the idea that these plates could pull apart and that the continents were moving was not widely accepted because it just like, seemed a little unlikely. 

Instead, a lot of people including Heezen held up an idea called "expanding earth" which said that the continents were pulling apart because the actual volume of the earth was increasing, like we're a balloon. But then came Tharp's rift valley, this gigantic cleft that just looked suspiciously

like a place where tectonic plates were pulling apart, and today we know that's exactly what it is. We call it the mid-Atlantic ridge. And there, the tectonic plates are being shoved apart as hot material from inside the earth rises to the surface. This ridge ultimately gives us a mechanism for continental drift and it was a nail in the coffin of the expanding earth idea. 

But back when Tharp shared those thoughts with Heezen, he called the idea "girl talk" and asked her to redo her calculations. And so Tharp did, and she found, like maybe unsurprisingly, there was a rift valley still there. 

Also, to add even more evidence, it turned out that another assistant in the lab was making a map of earthquake epicenters and the earthquakes were forming in the same spot as Tharp's rift valley. Since earth quakes are formed by the movement of tectonic plates, this made it clear that the rift valley was between two tectonic plates and they were pulling apart. 

And now, continental drift is foundational to our understanding of the planet and how it changes. Like among many other things, it explains why some of the continents look like they used to be connected. Becayse they were. And it might have taken us longer to understand that without Tharp's maps. In the end, Tharp studied the ocean floor until her death in 2006. Along the way, besides like, proving continental drift is a thing, she also made some more incredibly detailed maps of the deep ocean and she worked constantly on understanding the mid-Atlantic ridge and other systems like it, so while we have a lot left to learn about the ocean, Marie Tharp gave us an enormous shove in the right direction. We now have a new appreciation for the world beneath the water and how rift valleys are changing the world beneath our feet too. 

////// The Mid Atlantic ridge wasn't the only unexpected geologic feature we found in the water though, we've also found a collection of white smoking towers that make up an area scientists have named "the lost city" and they might have something to do with the origin of life. 

There's a good chance you've heard of hydrothermal vents located in the deep ocean thousands of meters from the surface, these towering chimneys spew black acidic metal-rich water from deep within the earth. Hydrothermal vents are some of the most extreme environments on the planet and home to some of the most interesting creatures alive. But in 2000 scientist discovered a vent unlike any other. One not quite so deep down with white chimneys that's been around about 10 times longer than any other vent fume and some of them think it may help us understand how all life began. The researches on the Alvin submersible weren't looking for a massive hydrothermal vent field when they were exploring a mountainous region of the Atlantic sea floor about 750 to 900 meters below the waves. They basically stumbled upon it, a sprawling field of huge white spires and chimneys up to 60 meters tall. Because of these dramatic structures and the site's location on the Atlantis massif, the researchers named the site the Lost City Hydrothermal Field and it turns out lost city is really different from other hydrothermal vents. Most vents are what scientist call black smokers and they form where there's lots of volcanic activity.

In those cases, water in the Earth's crust gets superheated by underground molten rock and bursts out into the deep ocean. We're talking water that's hotter than boiling - like up to 400 degrees Celcius, which is only kept from becoming gas by the intense pressure of the deep sea. This super hot water strips the rock it comes into contact with of minerals like iron sulfide, which turns it black. 

Lost City's white smoker chimneys are basically the exact opposite of that, because they form by a process known as serpentinization instead. It occurs when seawater meets olivine, a greenish material containing magnesium, iron, and silicate. You might actually have seen some of this stuff before, the gem quality version is known as peridot. Olivine is formed naturally in the Earth's mantel, that viscous layer of molten rock below the crust, and at Lost City the olivine-rich mantel is closer to the surface than usual, perhaps because it sits near the intersection of a mid-ocean ridge and a fault. Whatever the reason, the mantel is close enough that seawater can seep down through the small cracks in the crust and come into contact with this olivine. 

and that sets off a chemical reaction. As water infiltrates the gaps of olivine's crystal structure, it changes into serpentinite. As that happens, some of the oxygen atoms combine with the iron from the olivine to form magnetite, and the hydrogen atoms come together to make hydrogen gas. But in the presence of carbon dioxide, like the carbon dioxide that's in seawater, something else happens.

Carbon atoms from the CO2 and those extra hydrogen atoms from the serpentinization come together to form methane gas - which for the record makes Lost City really special, but we'll get to that in a bit.

The important things to know for now are that these reactions give off some heat, so the surrounding water gets a little toasty, but only about 40 to 90 degrees Celcius, so it's cool in comparison to black smokers. And during this process, CO2 gets removed from seawater, which ultimately makes the water much less acidic.

You see, dissolved carbon dioxide reacts with ocean water to form carbonic acid, which can further react with water to form carbonate and bicarbonate ions. That ultimately releases hydrogen ions and, therefore, makes the water more acidic.

If you remove CO2 though, the reactions go the other way, which is why the chimneys at Lost City have a pH of about 9, closer to baking soda than plain water. That's the exact opposite of other hydrothermal vents, which spew very acidic water. It also happens to be why Lost City has white smoke.

You may have heard of the mineral calcium carbonate, because its that white stuff that shells and corals are made of, and it's an awesome building material - if your water isn't too acidic. If it is, those roaming hydrogen ions will react with the carbonate ions instead of the calcium. Hydrogen and calcium ions are both positively charged so when they're in seawater, both could potentially pair up with negatively-charged carbonate ions.

But what usually happens is a hydrogen covalently bonds to the carbonate, turning it into bicarbonate, which even though it's negatively charged, the positive calcium ions don't do much with. If you raise the pH and remove those hydrogen ions, the carbonate stays carbonate and can combine with calcium. And voila - you get white tinted water. There's one more way

Lost City differs from most hydrothermal vents - it's a lot older. Black smokers are fueled by the heat from volcanic activity and once that source of heat is consumed, or otherwise disappears thanks to tectonic shifts, they die. Since Lost City doesn't rely on the fickle whims of volcanic activity to flourish, it's estimated to be 120 thousand years old, roughly 12 times the age of its black smoker cousins.

And it doesn't seem to be in danger of dying anytime soon, so Lost City is a pretty fascinating place. But it doesn't just stand out amongst hydrothermal vents, it may also give us clues as to the origin of life.

Even if life didn't begin in the ocean, there's plenty of it there now. And some of these animals have taken advantage of the bounty of minerals under the water. Take this snail for instance, it's managed to evolve an iron shell. Here's one from Olivia.

OLIVIA: Deep below the Indian Ocean, in some of the most extreme environments on earth, there's a snail that has developed a unique and incredible strategy for protecting itself from danger. It built itself an iron suit of armor.

It's called the scaly-foot snail or Chrysomallon squamiferum if you want to get technical. Its name comes from the hundreds of stiff dark scales that cover its fleshy foot, the part of the snail's body it uses to scootch around.

These snails were first reported in 2001, living near hydrothermal vents on the seafloor. They hang out in the geothermally heated waters while bacteria in their throats provide nutrients for them. And scientists were immediately intrigued by the snail's bizarre armored appearance. Then under closer inspection, things got even weirder.

It turns out those dark scales and the snails' shells are coated in a layer of iron. Specifically, they contain iron-sulfide compounds, which are molecular combinations of iron and sulfur. In this case the compounds are mainly pyrite, a mineral commonly called fool's gold, and greigite, a mineral similar to magnetite which

makes the scales and shells slightly magnetic. Interestingly, the snails only wear this suit of armor some of the time. As of 2018, this species has been spotted at three different hydrothermal vent locations in the Indian Ocean. And at one of those locations, the waters lack iron sulfide, which is likely why the snails do too.

But in the other two spots where the venting fluids are rich in iron compounds, the snails are somehow able to harvest the minerals for themselves. No other animal is known to incorporate iron into its skeleton, or in this case exoskeleton. So scientists have been trying to figure out how these snails acquire their suits of armor and what they're used for.

At first, researchers suspected the iron might come from bacteria that thrive in hydrothermal waters. Specifically, bacteria that can survive the lack of oxygen because they essentially "breathe" sulfate instead, a process which produces iron sulfides as a side-effect. But a 2006 study found that the chemical signature of the snails' iron is a better match for the iron-rich hydrothermal fluids than anything forged by bacteria. 

So the snails seem to be building their own armor using iron from the water around them. See the iron in the water near these vents can naturally react with certain kinds of sulfur to make iron sulfides. So the idea is by regulating where and how that sulfur is available, the snails might have control over the formation of their mineral armor.

Exactly how they do this, though, isn't clear. As for why they have this armor, well protection from predators seems to be an obvious answer. A 2010 study found that the iron shell has a multi-layered structure that makes it extra resistant to fracturing or bending. On top of that, the foot scales are reportedly harder and stiffer than the enamel coating on your teeth.

So the snail armor seems pretty perfect for resisting any attacks from the predatory crabs and snails in its ecosystem. It may even serve as a model for humans to build extra strong materials. But we'll need to be careful not to wipe out the snails first.

See, in 2018, they were officially classified as an endangered species, because the vents they live on are targeted for mineral mining.

Some of their habitat has likely already been disturbed. But hopefully, we can keep them around and they'll have a lot more to teach us. 

Michael: So far we've talked about mid-ocean rifts, minerals, and hydrothermal vents, and now, it's time to tie all those things together. For one last video, here's the story of how the ocean floor got filled with riches. 

Underneath kilometers of seawater, the ocean floor is full of riches. There's gold, iron, and lots of other rare, precious metals. And no, it doesn't have anything to do with pirates. All this treasure is the result of millions of years of geochemical processes that have been steadily filling the sea floor with loot.  Some of the most impressive deposits grow at hydrothermal vents, which are hot springs at the bottom of the ocean.

These vents form along mid-ocean ridges, where Earth's tectonic plates are splitting apart, and lava rises up through the gap, then hardens into long, underwater mountain chains. At these spots, sea water seeps into the cracks in the ocean crust, and collects underground, where it gets heated by magma and bursts out through the vents.  But it's not pure seawater that comes back out. The whole time it's underground, the hot seawater is leeching metals from the surrounding crust, which is full of huge amounts of sulfur, along with metals including copper, gold, zinc, lead, and silver.

So when that hot water gushes back out from the vent, it interacts with the cold water around it, and all those dissolved metals precipitate back out into the liquid. Over time, they form tall, chimney-like structures that rise up around the vent. Sometimes, the chimneys are called white or black smokers because the erupting fluids full of minerals look like smoke rising out of the towers.

But the whole accumulations are known more formally as "massive sulfide deposits." These can only form under the ocean, but these days, when we mine for zinc, copper, or silver on land, we're often mining massive sulfide deposits that originally formed on the ocean floor millions of years ago.

It's just that since then, they've ended up above sea level, thanks to the shifting of tectonic plates.

For example. the island of Cyprus has 30 of these massive sulfide deposits that were once under the sea, and that's where the ancient Romans got their copper. Unlike hydrothermal vents, though, some underwater deposits accumulate much more subtly.

Such as the ones that grow on exposed ridges, plateaus and underwater mountains left behind by extinct volcanoes. As seawater comes in contact with these surfaces, metals dissolved within it precipitate out to form a crust over the rocks. It all starts when iron and manganese oxides latch onto the rock.

They're prone to chemical reactions and have a lot of surface area, which makes them especially sticky as far as chemicals go. So they'll glom onto any exposed rock surface. Then, once these compounds build up enough, they form a sponge-like network that traps other metals from the seawater in the pores.

Seawater itself has pretty low concentrations of metals, but as those metals collect on exposed surfaces, they can reach concentrations 1 billion times higher than in the ocean. These so-called cobalt-rich crusts contain metals like cobalt, iron, and manganese, as well as rare earth metals like tellurium and platinum. And depending on the strength and direction of the ocean currents, the crust can form just a glaze, or it can grow to be about 25 cm thick.

But these crusts grow incredibly slowly. Every million years, they accumulate just one to ten mm! It's one of the slowest processes on Earth.  Finally, the last process we're gonna look at in our tour of the sea floor produces what might be one of the oddest of our ocean treasures.

A potato-shaped clump made of minerals containing manganese, iron, and smaller amounts of other metals. These lumpy rocks are known as manganese nodules, and they grow in underwater fields more than 3500 meters below the surface. Each nodule gets its start as a piece of debris, like a shark tooth or a pebble, that serves as a nucleus.

Then, little by little, manganese and iron oxides attach to the debris, just like they attach to exposed rock, and over millions of years, the metals grow in concentric rings, kinda like a jawbreaker candy.

All this iron and manganese comes from seawater, and also from liquids that squeeze out from pores in the sediments beneath the rocks.

Scientists think that the nodules also get a little help from special bacteria that live on them. They believe these microbes speed up the process by taking manganese from the seawater, converting it to manganese oxide, and depositing it on the clump.

These odd treasures were discovered in 1873 during the first ever worldwide oceanographic expedition. The crew of that expedition dragged up a few lumpy rocks from the sea floor and were surprised to find they were big hunks of manganese oxide. Today, we know that there are thousands of square kilometers of these nodules growing on the sea floor, and they contain more manganese than there is anywhere on land.

Since their discovery, these sea floor treasures have generated a lot of interest, both from scientists and mining companies. Many of these metals are in short supply on land, but are in demand from manufacturing high-tech electronics, like cell phones and rechargeable batteries. But since the ore lies beneath hundreds of meters of water, no one is mining these deep-sea treasures.

Yet. Which is a good thing, because we don't fully understand how that would alter seafloor ecosystems, or the larger ocean environment. After all, as common as they are, the ocean floor has been growing these treasures for millions of years.

So we know they don't come easy, which gives us all the more reason to protect them. 

So, from marine snow all the way down to the floor below, there's a lot to see in the ocean. In many ways, the geology down there is just as fascinating as the weird creatures. That said, there are a lot of bizarre creatures in the ocean. If you'd like to learn more about them as well, you can watch another compilation after this.  (outro music)