Humans are obsessed with the sky. We spend billions to look at rocks on Mars, but we barely know what’s happening seven miles straight down. Honestly, it’s a bit weird. When you ask how deep in the ocean have humans gone, most people think of a scuba diver or maybe a submarine from a movie. The reality is much more claustrophobic, incredibly dangerous, and limited to a tiny handful of people.
We’ve reached the absolute bottom.
That place is the Challenger Deep. It sits at the southern end of the Mariana Trench, roughly 35,800 feet below the surface. To put that in perspective, if you flipped Mount Everest upside down, you’d still have over a mile of water above the peak. It is a crushing, pitch-black void.
The Pioneers and the Iron Pot
Back in 1960, two men did something that most people thought was a suicide mission. Jacques Piccard and Don Walsh climbed into a vessel called the Trieste. It wasn't really a "ship" in the way we think of them. It was a bathyscaphe—basically a giant float filled with gasoline (because gasoline is lighter than water and doesn't compress) with a tiny steel sphere attached to the bottom.
They spent nearly five hours descending.
The walls were thick. The window was tiny. At one point, one of the outer plexiglass window panes actually cracked. Imagine being seven miles down and hearing a loud pop. They stayed at the bottom for only twenty minutes, and they couldn't see much because they kicked up so much silt. But they proved it was possible. They reached approximately 35,797 feet. For decades, that was it. Nobody went back. It was too expensive, too risky, and there wasn't a "Space Race" for the ocean to justify the cost.
James Cameron and the Vertical Torpedo
Fast forward to 2012. Most people know James Cameron for Titanic or Avatar, but he’s also a legitimate deep-sea explorer. He spent seven years secretly building the Deepsea Challenger in Australia. Unlike the Trieste, which was a horizontal tank, Cameron’s sub was a vertical torpedo. It was designed to sink fast and come up even faster.
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He went down alone.
When you're looking at how deep in the ocean have humans gone, Cameron’s solo dive stands out because of the tech. He used specialized syntactic foam to keep the vessel buoyant at pressures that would turn a normal submarine into a soda can. He reached 35,787 feet. He described the bottom as "desolate" and "lunar." There were no sea monsters. Just tiny amphipods and a sense of total isolation.
Victor Vescovo and the Regular Commute
If Piccard was the pioneer and Cameron was the adventurer, Victor Vescovo turned deep-sea diving into a repeatable science. Between 2018 and 2019, Vescovo—a private equity investor and retired naval officer—funded the Five Deeps Expedition. He didn't just want to hit the Mariana Trench; he wanted the deepest point in every single ocean.
He used a craft called the DSV Limiting Factor.
This thing is the "Tesla" of the deep sea. It’s a titanium-hulled two-person sub built by Triton Submarines. Vescovo ended up going to the bottom of the Challenger Deep multiple times. In May 2019, he reached a record depth of 35,853 feet. He even found a plastic bag down there, which is a pretty depressing commentary on the state of the planet.
Since Vescovo’s successful runs, several others have made the trip, including Kathryn Sullivan, who was the first American woman to walk in space and is now the first woman to reach the ocean's deepest point. This is where we are now: we have the technology to go to the bottom, but it's still restricted to the ultra-wealthy or the ultra-specialized.
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Why Can't We Just Go Deeper?
You might wonder why "only" 35,000-ish feet is the limit. It’s because that’s where the floor is. There isn't a "deeper" unless we start drilling into the Earth's crust. But the physical challenge of getting there is mostly about pressure.
At the bottom of the Mariana Trench, the pressure is about 16,000 pounds per square inch.
Think about that. It’s like having an elephant stand on your thumb. Or, more accurately, like having an entire fleet of jumbo jets stacked on top of you. Water doesn't compress, but air does. Any tiny pocket of air in a submarine—or in a human lung—will be crushed instantly if the hull fails. This is why scuba divers can't even get close.
- Scuba World Record: Ahmed Gabr reached 1,090 feet in 2014. It took him 15 minutes to go down and nearly 14 hours to come back up to avoid the bends.
- Military Submarines: Most nuclear subs stay above 1,500 to 2,000 feet. Any deeper and they risk a hull collapse.
- The Hadal Zone: This is the area from 20,000 to 36,000 feet. Only specialized "landers" and a few specific manned submersibles can survive here.
The Physics of the "Deep"
The ocean is divided into layers. The Sunlit Zone is where the fish you eat live. Then you hit the Twilight Zone, where the light fades. By the time you get to the Midnight Zone (3,300 feet), it is pitch black. Most people don't realize that how deep in the ocean have humans gone is a question that usually ignores 99% of the water column. We mostly "visit" the bottom; we don't "live" or "stay" there.
Temperature is another killer. It’s just above freezing at the bottom. But near hydrothermal vents, the water can hit 700 degrees Fahrenheit. The only reason it doesn't boil is because the pressure is so high. It’s a world of extremes that feels more like an alien planet than part of Earth.
What’s Actually Down There?
We used to think the deep ocean was a desert. We were wrong.
Even at the crushing depths Vescovo reached, life exists. We've seen snailfish at 26,000 feet. They look like translucent tadpoles, and their bones are made of cartilage that handles pressure better than hard bone. Their proteins are even folded differently so they don't "clump" under the weight of the water.
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There are also "xenophyophores." These are giant, single-celled organisms that look like sponges or clumps of dirt. They soak up heavy metals and thrive in the dark.
The Future of Deep-Sea Exploration
We have better maps of the Moon and Mars than we do of our own sea floor. Only about 25% of the ocean floor has been mapped with high-resolution sonar. The rest is just an estimate based on satellite data.
The next step isn't necessarily sending more people down in tin cans. It’s about ROVs (Remotely Operated Vehicles) and AUVs (Autonomous Underwater Vehicles). These drones can stay down for days or weeks, filming and sampling without worrying about life support. Companies like OceanX and government agencies like NOAA are using these to find shipwrecks and new species every year.
However, there is a push for "Deep Sea Mining." This is controversial. Some companies want to go deep to collect "polymetallic nodules"—basically rocks filled with cobalt and nickel for EV batteries. Critics, including marine biologist Sylvia Earle, argue that we’ll destroy ecosystems we haven't even discovered yet.
How You Can Track This
If you're interested in the ongoing exploration of the deep, you don't have to be a billionaire.
- Watch Live Streams: NOAA’s Okeanos Explorer often live-streams their ROV dives on YouTube. It’s weirdly relaxing to watch a robot discover a "Dumbo Octopus" in real-time.
- Follow the General Bathymetric Chart of the Oceans (GEBCO): They are the ones trying to map the entire floor by 2030.
- Check out the DEEP project: This is a newer initiative looking to create permanent underwater habitats at depths of up to 200 meters, which would change how we interact with the "shallow" deep.
Understanding how deep in the ocean have humans gone helps us realize how small we are. We've touched the bottom, yes. But we've only spent a few hours there. The ocean is vast, heavy, and mostly indifferent to our presence. Exploring it is arguably the hardest thing humans do—harder even than going into orbit.
Next time you look at the beach, just remember: there is a seven-mile drop out there somewhere, and we've barely scratched the surface of what’s hiding in that dark.
Actionable Insights for Ocean Enthusiasts:
To stay informed on deep-sea milestones, follow the Schmidt Ocean Institute's vessel, Falkor (too), which frequently discovers new seamounts. If you want to visualize these depths, use the Deep Sea Map tool from ESRI, which provides a 3D perspective of the Mariana Trench compared to global landmarks. For those interested in the engineering side, study the design of syntactic foam, the unsinkable material that makes modern deep-sea exploration possible.