We've Only Seen 0.001 Percent of the Deep Ocean
That's only about the size of Rhode Island
Hiya!
I used to assume that we prioritize space exploration because we’ve learned all we can about Earth. Then I discovered how little we actually know about our planet, especially the ocean, which encompasses the majority of Earth’s surface. Advanced technology, such as sonar, and projects like Seabed2030 are helping to reveal the deep-sea’s topography, but they can’t show us the life that inhabits the cold, dark depths of the ocean.
Then, a few years ago, a marine scientist wondered how much of the deep sea we’ve actually seen. After finding conflicting results, she enlisted the help of her colleagues and discovered that we’ve observed far less of the deep sea than anyone thought, and the areas we have surveyed are restricted to those around specific countries and limited to certain geographic landscapes.
The Deep Ocean
The surface area of the global ocean is about 139 million square miles (360 million square kilometers), covering approximately 70 percent of Earth’s surface. Not only is the ocean expansive, but an estimated 90 percent of it is considered “deep sea,” with an average depth of 12,080 feet (3,682 meters).
Its colossal size makes the global ocean Earth’s largest livable space, with more life inhabiting it than anywhere else on the planet. In particular, the cold, dark, highly pressurized deep ocean, defined as being deeper than 656 feet (200 meters), is home to bizarre creatures like the pelican eel and marine hatchetfish, as well as an untold number of diverse ecosystems.
The deep ocean also makes up the single largest portion of Earth’s biosphere and plays many essential roles in maintaining the health of our planet, including oxygen production, climate regulation, and providing vital pharmaceutical resources.
One may assume that, considering the ocean’s massive size, ecosystems, and substantial contributions to a healthy planet, we’d prioritize learning as much as we can about it, at least as much, if not more so, than learning about Space. Yet, for as much as we’ve learned so far, we’ve barely scratched the surface.
It was not until 1977 that researchers discovered life in the form of microbes thriving around hydrothermal vents, utilizing the chemical reactions in the vents for energy rather than needing sunlight or photosynthesis to survive.
Katy Croff Bell, a deep-sea explorer and founder of the nonprofit Ocean Discovery League, who led the new research I’ll tell you about soon, explained to Madeleine Cuff of New Scientist,
"That was completely revolutionary and completely rewrote all the science books. Now we know that you can have entire ecosystems that originate in darkness and feed off this hot, mineral-rich water coming up out of the seafloor.”
Based on what we’ve discovered in the decades since then, it’s clear that the ocean possesses dramatically different ecosystems that support highly diverse lifeforms.
Scientists estimate there are potentially between 700,000 and 1 million oceanic animals (excluding microorganisms, which number in the millions), with only around a third identified to date. However, the list is growing rapidly, with almost 2,000 new species added to it each year.
Learning more about them is tricky, though.
Limitations of Deep Ocean Exploration
A significant challenge to oceanic exploration is that it becomes darker and more pressurized the deeper we go.
The pressure at sea level is typically referred to as “one atmosphere,” a unit equivalent to almost 15 pounds of pressure per square inch (psi). However, the pressure increases by another atmosphere for every 33 feet (10 meters) as we descend into the salty ocean.
For reference, without specialized equipment, the average recreational diver can safely dive to a maximum depth of only 130 feet (40 meters), where the pressure is approximately five times that of the surface.
Meanwhile, professional and technical divers can safely reach depths of 330 feet (100 meters) or more, but this requires extensive training and experience. Going deeper can result in major health issues, while at extreme depths, the pressure can crush the human body.
As a result, we understandably rely more on technology to map, sample, and explore the ocean depths. For instance, using technology like sonar to map the seafloor’s topography, which is the premise of The Nippon Foundation-GEBCO Seabed 2030 Project (Seabed2030).
Seabed2030 is a global initiative involving governments, research institutions, philanthropists, NGOs, and civil society to create a comprehensive map of the entire seabed by 2030. As of June 2024, they report that 26.1 percent of the global seafloor had been mapped.
Technologies like sonar can tell us a great deal about the shape and landscape of the seafloor, but they reveal next to nothing about what might inhabit the areas. To learn that, we gotta see what’s down there.
Lowering imaging technology, such as remotely operated vehicles (ROVs), into the ocean depths is the obvious first choice to provide us with imagery. However, even this is challenging, especially beyond the Mesopelagic Zone, which is an ocean layer ranging from 656 feet (200 meters) to 3,300 feet (1,000 meters) deep.
The Mesopelagic Zone is also known as the Twilight Zone because light struggles to penetrate it, leaving everything below it in darkness. And the dark is a problem when we’re trying to see, even with lights. As Bell explained to Nell Greenfieldboyce of NPR,
“when you’re down there with a remotely operated vehicle or other sort of deep-submergence vehicle, you can only see a very tiny bit of the deep-sea floor at any one time.”
Not to mention that to get these glimpses is highly laborious and expensive. Bell told Rebecca Dzombak of the New York Times that it can cost between $2 million and $20 million to explore just 0.39 square miles (one square kilometer) of the deep seafloor.
Despite the challenges, Bell has studied and explored the deep-sea for nearly a quarter century, but she told Greenfieldboyce, it wasn’t until four or five years ago that she began to wonder,
“Well, how much have we actually seen? And I started trying to find that statistic."
Rather than finding a specific answer to her curiosity, Bell found estimates ranging from less than one percent to as much as 10 percent. Unsatisfied with the results, she decided to work out a more precise estimate herself with the help of her colleagues at the Ocean Discovery League.
New Research
Bell and her colleagues gathered and analyzed records from approximately 44,000 deep-sea dives that took place in 120 countries between 1958 and the present.
These records included everything from simple, stationary landers to human-driven submarines and ROVs. They also took into account that some dive records aren’t public.
By the end, the team was stunned by the results and discovered far more than they expected.
The Results
Regarding Bell’s initial curiosity, the team found that we’ve explored shockingly little of the deep ocean.
We may have 26 percent of the ocean floor mapped thanks to sonar and Seabed2030, but Bell and her team’s analysis revealed that we’ve only visually observed a maximum of 1,476 square miles (3,823 square kilometers), or less than 0.001 percent of the deep seafloor. That’s about the same size as Rhode Island, or a tenth of the size of Belgium. The researchers explain in the study,
“It’s like if we were to make all assumptions about terrestrial ecosystems from observations of 0.001% of land area, that would equate to smaller than the land area of Houston, Texas.”
And according to a statement,
Given that not all dive records are public, the researchers assert that even if these estimates are off by a full order of magnitude, less than one-hundredth of 1% [0.01 percent] of the seafloor would have any visual records.
Even then, not all visual records are created equal. The researchers found that any visuals of the deep seafloor captured before 1980 (which make up almost 30 percent of all known visual observations) are black and white and mostly of poor quality.
Furthermore, the researchers identified some patterns in the imagery they analyzed.
For one thing, over 65 percent of the observations were made within 200 nautical miles of Japan, New Zealand, and the United States. Adding Germany and France to the equation boosts it to 97 percent.
The team also discovered a landscape bias, as certain deep-sea topographical features, such as canyons and ridges, have gained far more scientific attention than seamounts or abyssal plains. As a result, we don’t have a very accurate sample of what the seafloor is like around the globe. Bell explained to Greenfieldboyce that,
"given how little we've seen and how biased it is, we can't really give you a global map of all the habitats of the deep sea, because we just haven't been to all of them.”
She adds, "The Indian Ocean is one of the least explored areas."
The study, published in Science Advances in May 2025, provides the most comprehensive global estimate of deep-sea observations to date, highlighting the disparity in global exploration efforts.
As geologist and deep-sea expert Jeffrey Karson of Syracuse University, who wasn't part of this research team, explained to Greenfieldboyce:
"We're spending a lot of money to try to understand other planets, maybe planets outside of our solar system. And yet right here on our own planet, we know so little of what's going on in this area that covers about two-thirds of our planet.”
"Almost every time we go there, we learn something new and exciting, and many of our discoveries on the seafloor have been serendipitous. So, you know, we're feeling our way in the dark, literally, there."
Still, Karson said that while he assumed humanity has only seen less than 1 percent of the deep-sea floor, he was still surprised the percentage Bell and her team found was “such a tiny number.”
In the Future
The study emphasizes the need for more extensive exploration of the deep oceans and identifies target areas for future research to provide a better representation of the global ocean floor.
The researchers suggest boosting support for low- and middle-income countries to develop affordable deep-sea tools, thereby expanding access to research.
Jon Copley, a marine biologist at the University of Southampton in England who wasn’t involved in the study, told Greenfieldboyce:
“If I were a billionaire philanthropist and I wanted to make a real dent in exploring the ocean, then rather than building a kind of superyacht research ship, I would fully back the development and growth of these kinds of low-cost platforms.”
The reasons for the increasing oceanic exploration go far beyond simply curiosity, however. Bell reminded Greenfieldboyce that while the deep ocean may be out of sight — and out of mind for most people — it plays many vital roles in the health of our planet. She says,
"All of these things are connected, and impact us in so many different ways.”
She explains further in a statement,
“As we face accelerated threats to the deep ocean—from climate change to potential mining and resource exploitation—this limited exploration of such a vast region becomes a critical problem for both science and policy.”
Setbacks
Unfortunately, despite the urgency in learning more about our global ocean and the ecosystems and life that call it home, Bell and her team’s study was published just after President Trump signed an executive order to fast-track the exploitation of deep-sea resources through mining.
The order has faced widespread international condemnation, especially from scientists who argue that more research is needed to better understand the impacts that mining in deep-sea ecosystems may have, most of which are completely unknown.
Perspective Shift
I’ve noticed an increased interest in oceanic mining for rare earth minerals, the installation of windmills for energy, and, of course, drilling for oil in our oceans over the last several years.
To me, such “progression” in many ways mirrors what happened during the Industrial Revolution, in assuming Earth’s resources are endless and being ignorant of the massive impact of our ravenous desire for power has on our planet’s health and stability.
Except now, we know better. So I wholeheartedly agree with the scientists who urge caution. Bell’s research is a huge flag, showing how little we know about the global ocean, and we all know what tends to happen when we mess with things we don’t fully understand.
Regardless, the fact that we’ve only seen about 0.001 percent of the global seafloor is wild. That means 0.999 percent remains unknown. Think about that for a moment. We search the universe for planets and wonder about alien life, yet our own oceans are essentially an alien world — one that’s part of but wholly separate from the terrestrial one we inhabit. Who knows what might be down there?
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Interesting and surprising.