Only around 10 submersibles are certified to dive deeper than 13,000 feet. Credit: Tahsin Ceylan / Anadolu via Getty Images Get the Popular Science daily newsletter💡 We know next to nothing about Earth’s seafloors. According to a study published May 7 in Science Advances, humans have only put eyes on 0.0001 percent of our planet’s waters deeper than the benthic zone’s boundary, about 656 feet below the surface. And for reference, the average oceanfloor depth is around 12,080 feet. Don’t expect that percentage to change anytime soon, either. The study’s authors at the Ocean Discovery League in Rhode Island estimate that even if 1,000 remote and piloted deep sea submersibles each traveled 1.86 square miles per day, it would take another 100,000 years to see it all. But there’s another major problem in this knowledge gap: what little we’ve seen is biased towards ocean regions selected by just five nations. This map displays the 822 square miles of total observed deep seafloor overlaid on the Philadelphia region. Credit: Ocean Discovery League Putting it in perspective You’ve probably heard this before: We understand more about outer space than we do about the deepest depths of Earth’s oceans. But knowing this and actually thinking about the numbers is another thing entirely. Roughly 70 percent of the planet is covered in ocean, and it contains far more life than the cumulative organisms on land. Scientists estimate there are somewhere between 700,000–1 million species living in the approximately 139 million square miles of water. After centuries of exploration, we’ve only catalogued about a third of those creatures. That’s not including microorganisms, by the way. If you want to add those to your tally, you’ll need to tack on a few more million to the total number of species. Even less is known about the seafloor itself. According to NOAA, just 26.1 percent of Earth’s ocean floors have been mapped using high-resolution technology, as of June 2024. That percentage is better when it comes to the seafloor in US waters: About 54 percent of that is accounted for—an area larger than all 50 states, Washington, DC, and the nation’s five territories combined. Deep-sea dive activity, 1958-2024. Deep-sea dive activity has been concentrated in a small number of locations, particularly in the US, Japan, and New Zealand. The heat map represents the number of dive activities per 96.5 square miles. The actual area observed on the seabed is too small to represent on a map at this scale. Credit: Ocean Discovery League Bias in the benthic zone But when it comes to seeing what’s down there—be it remotely or in piloted submersibles—the total is downright negligible. In their recent study, Ocean Discovery League researchers charted out 43,681 records from submersible expeditions undertaken by 14 countries across both 120 Exclusive Economic Zones (EEZs) and international waters. It’s from those statistics that they were able to calculate that humans still have 99.999 percent of the seafloor left to visually observe. What has been documented also illustrates a troublesome bias in geographic location. Most expeditions have taken place inside EEZs within 200 nautical miles of the US, Japan, and New Zealand. Combine those countries with France and Germany, and together they account for 97.2 percent of all dives. “This small and biased sample is problematic when attempting to characterize, understand, and manage a global ocean,” the authors wrote. According to the team, these estimates starkly lay out the need for a “fundamental change in how we explore and study the global deep ocean.” Aside from trying to accelerate the collection of visual data, the researchers contend that the scientific community needs to select a more intentional selection of target locations. “[W]hen explored, [these] will fill in the gaps and create the first unbiased and statistically representative biogeographical characterization of the entire deep seafloor,” they wrote. An uphill battle to the ocean floor Arranging these expeditions is easier said than done. Traveling to both the ocean floor and outer space offer uniquely daunting and dangerous challenges while requiring millions of dollars in funds for research, engineering, and construction. The number of missions beyond Earth’s atmosphere has literally skyrocketed in recent years, with over 2,800 launches in 2024 alone. Meanwhile, only about 10 submersibles in the world are currently certified for deep ocean travel. A major key to understanding Earth’s environmental complexities will require far more trips through the pitch-black ocean depths. Accomplishing that will require a more inclusive international approach to oceanographic exploration, as well as some serious patience.