Why More Than 80% of the Ocean Is Still Unmapped and Unexplored

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The ocean covers about 71 percent of Earth’s surface, yet much of what lies beneath it remains difficult to map, observe, and explore. National Geographic has reported that more than 80 percent of the ocean has not been mapped, explored, or even seen directly by humans. The comparison with Mars comes from the fact that much more of the surfaces of the Moon and Mars have been mapped and studied in detail than Earth’s ocean floor. There is an important catch in the word mapped. Broad satellite measurements can provide a general picture of the seafloor, but they do not reveal every mountain, canyon, wreck, or other feature in high detail. Modern multibeam sonar gives scientists a much clearer picture. As of April 2026, NOAA reported that 28.7 percent of the global seafloor had been mapped with modern high-resolution methods, while less than 0.001 percent of the deep-ocean seafloor has actually been visually observed by explorers. Exploration is difficult because most of the ocean is deep, dark, cold, and under enormous pressure. More than 90 percent of the ocean is deeper than 200 meters, and sunlight largely disappears below the upper part of the water column. Scientists therefore rely on specialized ships, sonar, remotely operated vehicles, autonomous systems, submersibles, and other instruments to study areas that people cannot safely reach themselves. The knowledge gap also applies to marine life. NOAA notes that scientists estimate hundreds of thousands to around a million ocean species may exist, with a large share still undiscovered or not formally described. New mapping technology and robotic exploration continue to reveal seafloor features, habitats, and organisms that were previously unknown. The ocean is not literally a blank space on a map, but enormous portions remain poorly observed at the level of detail needed for true exploration.