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The ocean is the largest ecosystem on Earth, but it's still mostly unexplored. This is partially due to the challenges of ocean exploration, like bone-crushing pressure and the need to bring your own air. But here are five ways that we've pushed the limits of where we can explore.

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The ocean covers over 70% of our planet, with an average water depth of 3500 meters, making it the largest ecosystem on Earth. It’s so huge, and so sparsely-explored, that it’s often referred to as inner space.

There are several challenges to exploring the ocean -- like the need to bring air. But pressure is where the ocean exploration can get really dangerous. Under water, every 10 meters of depth adds another atmosphere’s worth of pressure, compared to sea level quickly going from just a little squeeze to bone-crushing.

Still, these immense pressures haven’t stopped us from trying to reach the greatest depths possible, to learn as much as we can about inner space. And it’s not easy -- but here are five ways we can do it. Recreational SCUBA divers are warned not to dive deeper than 40 meters.

That’s because the compressed gases they carry for breathing underwater can become dangerous at higher pressures. During deeper dives, the added water pressure increases the amount of oxygen and nitrogen delivered to a diver every time they take a breath. And exposure to higher than normal concentrations of those gases can have a toxic effect on the diver’s body.

Oxygen toxicity due to high oxygen concentrations can cause seizures, lung failure, and even death. And nitrogen narcosis from too much nitrogen can cause a diver to feel disoriented or even lose consciousness. As you can imagine, both of these conditions would be dangerous while exploring underwater.

So, to prevent them from happening, deep water divers breathe trimix gases instead. This is a blend of three gases, usually oxygen, nitrogen, and helium. This blend reduces the amount of oxygen and nitrogen in the breathing mix and keeps them from reaching toxic concentrations, even at higher pressures.

Trimix gases expand the depth limit to 60 meters or more, depending on how experienced the diver is. And the use of trimix gases in scientific diving has helped researchers explore the twilight zone of the ocean, a zone that extends from 60 to 150 meters deep. This zone is too shallow to justify the costs of exploration with expensive technology like submersibles, so it’s one of the most unexplored regions of the ocean.

Divers exploring the twilight zone are discovering up to 10 new species per hour! Trimix gases are also often used in conjunction with a rebreather: a device that absorbs the carbon dioxide exhaled by the diver, allowing them to rebreathe the unused oxygen and inert gases from each breath. These are different from traditional SCUBA regulators, where the exhaled gas gets released as bubbles directly into the water.

Rebreathers extend the life of a limited supply of gas, as well as eliminate all bubbles which happens to provide an extra benefit for researchers attempting to observe particularly skittish creatures. Next are atmospheric diving suits, which are quite a bit like space suits. There are other ways to explore the deep ocean, but if you want to use your own arms and legs to interact with the environment, this is really the only option.

These things are more like wearable submersibles than anything else, and can be a bit clunky and hard to maneuver in perhaps even more so than a space suit, in fact. Still, the wearer can descend to depths of over 700 meters for several hours, with none of the dangers that come from SCUBA diving. The suits are able to keep their interior pressure at atmospheric levels, as well as provide several hours of air supply, so the wearer doesn’t even need to be SCUBA certified.

They’re also a fantastic way to explore the deeper marine environment without a lot of loud noise coming from engines, like on a submarine again, making things easier for skittish wildlife. Now, while they may resemble space suits, these were some of the earliest technologies used to explore marine environments for more than a few minutes at a time. The first one was developed in 1715!

The most recent iteration of this suit is called the Exosuit, which researchers want to use to study bioluminescence and biofluorescence at depths of 200 to 1000 meters. Many migrating fish, plankton, and other animals living in this depth range have these glowy properties, but scientists have only been able to study them with remote instruments or from samples found in trawl nets. The pressure at these depths can be 30 times greater than at the surface, and even the most experienced diver cannot safely explore in this zone.

Putting a researcher down safely at that depth, with no engine noise, would be a huge opportunity to learn more about this part of inner space. Bathyscaphes, at first glance, look a lot like a submarine. But they have no way to be maneuvered in the water, so they’re more like an underwater hot air balloon than anything else.

A bathyscaphe has a huge tank filled with gasoline to give it buoyancy. That’s because gasoline is both lightweight and resists being compressed, even at huge depths. To descend, the bathyscaphe is loaded up with enough iron shot to help it slowly sink down to the depths.

To ascend, that shot is released on the ocean floor, and the bathyscaphe floats to the top with the help of its gasoline-filled tank. This seems pretty simple compared to the fancier technologies available today but a bathyscaphe is what took humans to the deepest spot on our planet for the first time. In 1960, the Trieste successfully went all the way to the bottom of the Challenger Deep in the Mariana Trench, which is just over 11,000 meters deep.

The two men on board were able to observe for the first time that there was life even all the way down there. This observation lasted less than 20 minutes before they had to head back to the surface, thanks to a crack in one of the viewing windows. But in that short time span, they saw shrimp, fish, and lots of bioluminescence.

Bathyscaphes are no longer in use today, because the gasoline tanks could rupture and fill with water, which would send the vessel to the bottom with no way to reach the surface. But the success of the Trieste paved the way for future exploration attempts to reach the Challenger Deep, although none were successful until 2012 and it was a submarine that successfully made that journey. Submarines have allowed humans to visit depths much greater than we ever thought possible.

Deep submergence vehicles, or DSVs, can take people to the deepest depths of the ocean. And they have to be made of special materials to withstand the immense pressure. Surprisingly, the main material they’re made of isn’t a metal like titanium, but rather a material called syntactic foam.

This special foam is made out of millions of teeny-tiny hollow glass spheres suspended in an epoxy resin, and it can withstand crushing pressures while also providing the DSV with enough buoyancy to float back to the surface. The DSV known as DeepSea Challenger was designed specifically to take film director James Cameron to the Challenger Deep. 70 percent of this submersible was made of a syntactic foam specifically designed to withstand the pressures of Challenger Deep, which are over 1000 times the pressure that we experience on land. And generally, not only can submarines travel to great depths, but they’re also equipped with a whole suite of technologies to help researchers better understand the deep sea environment.

They have robotic arms and storage boxes to collect samples, high definition cameras, and a lot of lights to light up the depths of the deep sea. Early exploration with submarines blew the lid off of our current understanding of what’s down there. Thanks to a DSV named ALVIN, researchers in the 1970s discovered hydrothermal vents, as well as animals that thrive around them.

This led to the discovery of ecosystems that survive via chemosynthesis, a way for organisms to produce energy using inorganic materials rather than sunlight. Some researchers believe these vents may be where life itself originated at the bottom of the ocean, where the sunlight never reaches. And by the way, ALVIN is still at it after a decades-long career and tons of upgrades, this funky little submarine is still helping us explore.

Finally, there is a way to get around the technical limitations of sending humans to the bottom of the sea. And it involves… not sending humans. Remotely operated vehicles, better known as ROVs are like the Mars rovers of Earth.

They’re an extremely valuable piece of technology for exploring inner space, in part because they give researchers more time to explore. ROVs have all the capabilities of a submersible except the ability to hold people. They have robotic arms and storage boxes for sample collection, 4K cameras that capture tons of detail, and enough lights to light up a football field.

They can travel to the deepest parts of the ocean like, several ROVs visited the bottom of Challenger Deep before a submarine successfully made the journey. ROVs are generally operated from a ship at the ocean’s surface, connected to it by a series of cables. These do things like send a live video feed back to researchers onboard the ship, and provide a source of power.

Which means researchers aren’t limited by batteries or the need to use the restroom! And even though ROVs are comparable to probes we’ve sent to space, they have the distinct advantage of being a little closer to home so they can be brought in for maintenance, for example. This means endless observation opportunities, giving scientists the unique ability to experience the deep sea for what it is.

An ROV was used to discover the wreck of the Titanic in 1985. And since then, we’ve been using them to discover a number of other shipwrecks, as well as just… see what’s out there. And lest you think scientists are keeping all this cool stuff for themselves, you should know it’s actually possible to livestream from ROVs.

Which is making inner space more accessible to everyone! Exploring the depths of our ocean isn’t easy. But it’s worth learning more about inner space -- our planet’s biggest ecosystem.

We’re discovering new things every time we send a piece of technology into the ocean -- whether it’s a diver, a submarine, or an ROV. So, who knows what we will find next, way down there in inner space? Whatever it is, the right soundtrack is waiting.

Music for Scientists is an album inspired by the beauty and truth of science, as it expands our view of the world. It celebrates the idea that even the most remote parts of our universe, like the deep ocean, are ultimately knowable. It also celebrates the scientists who create that knowledge and share it with the rest of us.

After all, the human condition is all about knowing about grasping towards and expanding the limits of our world and of ourselves. If you think you’d enjoy Music for Scientists, you can stream the album on all major services or click the link below to catch the music video for “For Your Love”. [♩OUTRO].