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Fact check: What percentage of Earth's oceans remain unexplored by humans?
Executive Summary
The available analyses converge on a clear conclusion: most of Earth’s oceans remain unexplored, but the exact percentage depends on how "explored" is defined. Recent peer-reviewed work frames exploration both broadly—saying only 5–20% of the ocean has been explored over the last 150 years—and narrowly for the deep seafloor—reporting that as little as 0.0006–0.001% of the deep seafloor has been visually recorded, with profound geographic and national biases in coverage [1] [2] [3]. These figures reflect differing methods, timeframes, and emphases: regional, historical, and in situ visual observation.
1. A startling contrast: broad ocean vs. deep-sea visual coverage
The 2023 study argues that 5–20% of the ocean has seen exploration activity over the past 150 years, a broad metric that likely includes a mix of ship-based sampling, hydrographic mapping, and remote sensing rather than strict visual inspection [1]. By contrast, a 2025 study that quantifies visual coverage of the deep seafloor reports an almost vanishingly small fraction—0.0006–0.001%—observed directly by cameras or human-operated vehicles. These two numbers are not contradictory but rather show how definitional choices—what counts as “explored”—produce dramatically different conclusions about human knowledge of the ocean [2].
2. Why methodology drives the headline percentage
The broader 5–20% figure stems from aggregating multiple exploration modes over a long historical period, capturing varied data types and spatial scales, while the deep-seafloor estimate isolates visual in situ observation as the metric of interest [1] [2]. Visual observation is more resource-intensive and geographically constrained, which explains the negligible percentage for the abyssal realm. Method choice matters: remote sensing and sonar greatly expand mapped area but do not equate to biological or habitat-level understanding the way visual surveys do. That methodological trade-off is central when interpreting claims about “unexplored” ocean.
3. Geographic and national concentration of deep-sea knowledge
The 2025 deep-seafloor analysis highlights a stark concentration of in situ visual work: 65% of observations are within 200 nautical miles of just three countries—the United States, Japan, and New Zealand—and 97% of dives were by five countries (United States, Japan, New Zealand, France, Germany) [2] [3]. This reveals global inequality in exploration capacity and data distribution, meaning large ocean areas and many nations remain underrepresented in the observational record. The imbalance shapes scientific priorities, policy access, and benefit-sharing around deep-sea resources and knowledge.
4. Temporal and regional blind spots: where the unknown is greatest
Separate reviews of regional deep-sea work, such as on the Indian Ocean, underscore severe spatial and temporal data gaps, with research clustered in northwest and central areas while most of the basin remains poorly sampled [4] [5]. The 2023 and 2024 analyses both stress that lack of longitudinal time series and inconsistent spatial effort prevent robust assessments of biodiversity and climate impacts. These blind spots matter because the ecological and management implications of ocean change depend on representative, repeated observations across basins and depths.
5. Interpreting “unexplored” in policy and public discourse
The two dominant narratives—single-digit to low-double-digit exploration for broad measures versus near-zero for direct visual coverage—feed different policy conclusions. A claim that only 5–20% has been explored can motivate expanded multi-modal programs, while the 0.0006–0.001% figure emphasizes investment in deep, high-resolution observation and democratizing access to deep-sea platforms [1] [2]. Both narratives are valid if the audience understands the underlying metric; confusion arises when numbers are presented without that methodological context.
6. Potential agendas and why caution is warranted
Each source implicitly supports different priorities: the broad exploration estimate bolsters arguments for sustained, multidisciplinary ocean science funding, while the deep-seafloor statistic is often mobilized by advocates for targeted deep-sea exploration and equitable global participation. Treating these as mutually exclusive misleads; instead, acknowledge bias in framing and recognize that both larger-scale mapping and fine-grained visual surveys are necessary to close knowledge gaps [1] [2] [3].
7. Bottom line: what’s most defensible right now
Based on the provided analyses, the defensible headline is twofold: only a minority of the ocean has been meaningfully explored using diverse scientific methods (estimated 5–20% over 150 years), and an infinitesimal portion of the deep seafloor has been directly observed visually (0.0006–0.001%). Both figures are supported by peer-reviewed work from 2023 and 2025 and together convey that ocean exploration remains a large, unevenly distributed frontier with major implications for science, governance, and equity [1] [2] [3].