Humans have explored only a very tiny fraction of the ocean, especially its deep parts. According to a recent comprehensive study, just about 0.001% of the deep seafloor-defined as areas below 200 meters (656 feet)-has been visually observed by humans. This deep ocean covers roughly two-thirds of Earth's surface, yet the explored area is only about 1,470 square miles, approximately the size of Rhode Island

. When considering the entire ocean, including shallower regions, estimates vary but generally indicate that only about 20% of the ocean has been explored, leaving over 80% still unknown. Some sources say around 5% has been explored and charted in detail, especially with modern technology, while the rest remains uncharted and unseen

. Mapping efforts have progressed somewhat; for example, as of mid-2024, about 26% of the global seafloor had been mapped using modern sonar technology. However, mapping is different from direct visual exploration, which is far more limited due to the extreme conditions in the deep ocean such as high pressure, near-freezing temperatures, and darkness

. In summary:

• Deep ocean visual exploration: ~0.001% of the deep seafloor observed.
• Global ocean exploration (including shallow areas): Approximately 5% to 20% explored.
• Seafloor mapped by sonar: About 26% as of 2024.

The vast majority of the ocean remains a mystery, with significant implications for science, conservation, and resource management given the ocean's critical role in Earth's ecosystems and climate