We live on an ocean world. Yet we know surprisingly little about these oceans. In a new study published in Science Advances, researchers reveal that humans have visually documented just 0.001% of the deep seafloor—an area barely larger than Rhode Island.

“I knew it was going to be small,” Katy Croff Bell, the study’s lead author and founder of the Ocean Discovery League, told The New York Times. “But I’m not sure if I expected it to be quite that small.”

A Vanishingly Small Slice of the Unknown

The deep ocean begins at depths of 200 meters, a twilight zone that covers 66% of Earth’s surface. Yet after seven decades of deep-sea expeditions—nearly 44,000 dives analyzed by Bell and colleagues—scientists have visually observed only between 2,130 and 3,823 square kilometers of the deep seafloor. That’s less than one-tenth the size of Belgium.

“To provide an example for comparison,” the authors wrote, “if the scientific community were to make all assumptions about terrestrial ecosystems from observations of 0.001% of Earth’s land, it would be like judging all the world’s landscapes from an area smaller than Houston.”

Most of the seafloor data we do have comes from a very small group of explorers. The United States, Japan, and New Zealand account for 65% of all visual observations. Add France and Germany, and those five nations conducted 97% of dives with seafloor imaging. So we’re not just seeing a very small part of it all, we’re seeing a small part from a handful of sites.

“This small and biased sample is problematic when attempting to characterize, understand, and manage a global ocean,” co-author Susan Poulton told Gizmodo. “Imagine trying to tell the story of the African savanna or the Amazon rainforest using only satellite imagery and DNA samples without ever seeing what lived there.”

Why this matters

Why does it matter? Because seeing the seafloor is critical for understanding what’s down there—and how it functions.

For decades, scientists hauled up sediment and deep-sea life in dredged buckets. But without visual context, their interpretations were little more than educated guesses. The development of deep-diving submersibles like Alvin—which began operations in 1964—transformed the field.

“There are some habitats you can’t sample from a ship,” said Craig McClain, a marine biologist at the University of Louisiana who was not involved in the study. “You have to go there in an R.O.V. and do it.”

Photos and videos reveal ecosystems so alien they might as well be on another planet. In 1977, scientists discovered hydrothermal vents on the Galápagos Rift—cracks in the seafloor where hot, mineral-rich water gushes up, sustaining life that feeds not on sunlight, but on chemical energy. Entire communities of giant tube worms and blind crabs were found thriving in these sulfurous depths.

Since then, similar chemosynthetic life has been found around cold seeps, mud volcanoes, and even buried beneath the seabed. Some species discovered in recent years have challenged what we thought we knew about biology itself—including signs of “dark” oxygen production through electrochemical reactions on the seafloor.

A Tilted Map of Exploration

There’s another catch: we’ve mostly gone back to the same spots.

From Monterey Canyon to Sagami Bay, researchers have repeatedly visited a few easily accessible sites. Monterey Canyon alone accounts for nearly half of all visual observations of undersea canyons worldwide. Meanwhile, entire categories of terrain—such as abyssal plains and seamounts—remain underexplored, despite covering vast swaths of the ocean floor.

And we’re not even going deep. While the majority of the seafloor lies between 2,000 and 6,000 meters, most dives occur above 2,000 meters. The average dive has grown shallower over time. In the 1960s, over half of all dives exceeded 2,000 meters. Today, just a quarter do.

This imbalance is largely because diving deep is expensive and slow. Bell estimates a single square kilometer of exploration can cost between $2 million and $20 million. And a remotely operated vehicle moves slowly, covering only about 3 km² per year.

“If we kept exploring the deep seafloor at our current rate,” the authors wrote, “it would take more than 100,000 years to see it all once.”

Policy Racing Ahead of Science

The study arrives at a pivotal moment. Just days before its publication, the Trump administration signed an executive order accelerating deep-sea mining in U.S. waters—an industry that targets regions rich in minerals but low in data.

The deep ocean is already reeling from human impact. It has absorbed 90% of the planet’s excess heat and 30% of its CO₂, resulting in warming, acidification, and deoxygenation. Now, with mining and carbon dioxide removal technologies on the horizon, the threat to deep-sea ecosystems is growing.

And yet, our knowledge remains a tiny sliver. “More information is always beneficial, so we can make more informed and better decisions,” Bell said.

The deep ocean also holds solutions. Marine sponges have yielded drug candidates for HIV, breast cancer, and even COVID-19. Its cold waters help drive upwelling that feeds phytoplankton—the invisible plants that make up 80% of Earth’s oxygen.

“The deep ocean plays a key role in carbon sequestration and climate regulation,” Bell’s team wrote. They estimate the carbon stored there holds a social value of over $150 billion annually.

What’s Next?

This study lays out a roadmap to fix our ignorance.

The authors call for a “fundamental change” in deep-sea exploration. That means developing cheaper, autonomous tools that can be deployed by more countries—not just a wealthy few. Since the 2000s, there’s been progress: the number of platforms and operators has increased, and institutions in more nations are beginning to dive.

“If I were a billionaire philanthropist and I wanted to make a real dent in exploring the ocean,” Jon Copley, a marine biologist at the University of Southampton told NPR, “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.”

Bell agrees. “There are many people around the world that have deep sea expertise,” she said. “They just don’t have the tools to be able to do the kind of research and exploration that they want to do.”

It’s time, the authors argue, for oceanography to become more equitable and more ambitious. With a larger and more representative global effort, we might finally start to understand the true nature of the planet we live on.

“You can just imagine what’s in the rest of the 99.999 percent,” Bell said.