The seafloor, which covers more than two-thirds of Earth’s surface, is becoming increasingly disturbed by human activities. These include bottom trawling, a fishing method that drags heavy nets across the ocean floor, and potential future mining of manganese nodules, which are mineral-rich deposits found on the seabed. Such activities can disturb up to 2% of the global seafloor every year, affecting more than 200 square kilometers directly. In addition, the construction and maintenance of infrastructure such as anchoring points for ships, shipping lanes, underwater cables, and pipelines also impact the seafloor, often reaching depths of over 6,000 meters. The seafloor is more than just a surface; it plays a critical role in the Earth's systems, particularly in regulating the movement of carbon and nutrients between the ocean floor and the water above. Habitats like coral reefs, sponge beds, mussel beds, and microbial communities are vital for marine life and help maintain the balance of ocean ecosystems. Jacob Geersen, a marine geoscientist at the Leibniz Institute for Baltic Sea Research, emphasizes that the seafloor should be seen as a key component of the Earth system. Disturbances to it can disrupt carbon storage, nutrient cycling, and the stability of marine food chains. The Planetary Health Check (PHC) 2026 includes a new section focused on seafloor integrity, which refers to the preservation of the physical, biological, and chemical aspects of the seafloor. While this concept is not yet recognized as a formal planetary boundary, the PHC chapter explores how international laws and the precautionary principle can help protect the seafloor. It also highlights the legal and political challenges involved in managing human activities that affect the ocean floor. The seafloor plays a major role in the global carbon cycle, storing hundreds of billions of tonnes of organic carbon in the sediment layers of continental shelves. Bottom trawling, for instance, could release over 100 million tonnes of carbon from these sediments annually. However, the extent to which this carbon enters the atmosphere as carbon dioxide is still unclear. Levke Caesar, a climate researcher at the Potsdam Institute for Climate Impact Research, points out that the increasing strain on natural carbon sinks makes it essential to consider the seafloor as part of the Earth’s climate system. The Baltic Sea serves as a case study of the severe degradation of seafloor integrity caused by human activity, combined with environmental stressors like global warming, ocean acidification, and oxygen depletion. Researchers have found that no part of the Baltic seafloor remains untouched by human influence. The situation in the Baltic Sea may offer a glimpse into the future of other marine regions if the current rate of seafloor disturbance continues. To safeguard the seafloor, experts recommend that marine spatial planning and environmental assessments take into account the seafloor’s role in carbon sequestration and nutrient cycling, especially in deep-sea environments and carbon-rich sediments. A better understanding of the frequency and intensity of human activities on the seafloor is needed. The UN Agreement on the Conservation of Marine Biodiversity Beyond National Jurisdiction (BBNJ Agreement), which took effect in January 2026, supports the creation of marine protected areas and enhances environmental impact assessments. Scientists also stress the need to develop reliable methods for measuring seafloor integrity and its role in the Earth system, as there is currently no global standard for monitoring or protecting it.