The ocean covers over 70% of the Earth’s surface, yet a surprising amount of this vast realm remains unknown to humanity. Despite advanced technology used to study distant planets, the immense depths and hostile environment of the ocean present challenges far exceeding those encountered in space exploration. The total volume of the ocean represents 99% of the planet’s habitable space. The majority of this volume has never been seen by human eyes or high-resolution instruments. Most of the deep sea is a world still waiting to be discovered, holding secrets about our planet’s past and future.
Defining Oceanic Exploration
The percentage of the sea that has been explored is typically measured using two distinct metrics. The first metric is high-resolution bathymetric mapping, which uses sonar technology to determine the shape and depth of the seafloor. This detailed mapping, meeting modern hydrography standards, has covered between 26% and 27.3% of the global seabed as of mid-2024, largely due to international efforts like the Seabed 2030 project.
This mapping provides a topographical understanding of the ocean floor, revealing features like underwater mountains and trenches, but it is not a direct observation. The second metric is physical observation and sampling, referring to areas visually documented, touched, or sampled by researchers using submersibles or Remotely Operated Vehicles (ROVs). By this more detailed standard, the amount of the deep ocean seafloor that has been physically explored is estimated to be less than 0.001%. This minuscule fraction highlights the true extent of the uncharted deep sea.
Technological Constraints on Deep-Sea Research
The primary obstacles to widespread ocean exploration are the extreme physical conditions of the deep sea: crushing pressure, absolute darkness, and near-freezing temperatures. Below 200 meters, sunlight cannot penetrate, forcing explorers to rely on artificial light and specialized acoustic tools. The pressure at the bottom of the deepest trenches can be over a thousand times greater than at the surface, requiring prohibitively expensive and complex pressure-resistant technology for equipment.
The most common mapping technology is multibeam sonar, which transmits sound waves in a fan-shaped pattern and listens for the echo to calculate depth. While effective, the data resolution decreases significantly in deep water, meaning small but important features can be missed or vaguely defined. Deploying a research vessel equipped with this technology to survey the vastness of the ocean is a slow, costly, and time-intensive endeavor.
For close-up observation, scientists rely on uncrewed vehicles like Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs). AUVs, which follow pre-programmed paths, are constrained by finite battery life, often lasting only 8 to 60 hours depending on their design and mission intensity. High energy consumption is needed for propulsion and powering sensors, which drastically reduces mission duration. This combination of low speed, high cost, and limited endurance means that physical exploration progresses slowly compared to the ocean’s immense size.
The Value of Uncharted Waters
The effort to map the remaining 70%+ of the ocean is driven by the profound scientific and global benefits of understanding this hidden world. Mapping the seafloor is directly linked to the discovery of new life, as complex topography often creates biodiversity hotspots. In the deep ocean, scientists expect to find vast numbers of new species, many of which use chemosynthesis—relying on chemical energy instead of sunlight—near hydrothermal vents and cold seeps.
A detailed understanding of the ocean floor is also crucial for improving global climate models. The shape and depth of the seabed, known as bathymetry, influence deep-ocean currents, which in turn determine how heat is distributed around the planet. Accurate seafloor maps help scientists track and estimate the immense amount of carbon stored in marine sediments, a process known as carbon sequestration. Disturbing these carbon-rich sediments through activities like deep-sea mining could release vast quantities of carbon dioxide back into the water, highlighting the need to map these regions before they are exploited.