oceanfloor

The ocean floor, or seafloor, is the solid surface that forms the bottom of the world’s oceans. It consists mainly of oceanic crust, composed primarily of basalt, that sits atop the upper mantle and is covered by sediments. The ocean floor accounts for about 71 percent of Earth’s surface. Its average depth is about 3.7 kilometers, but depths vary widely, with the deepest points in submarine trenches such as the Challenger Deep in the Mariana Trench at about 10.9 kilometers below sea level.

Geologic structure: The floor includes continental margins (continental shelf, slope, and rise) that transition to deep-ocean basins. Major features include abyssal plains, mid-ocean ridges where new crust forms, fracture zones, trenches formed by subduction, and seamounts and guyots. Oceanic crust is newly created at ridges and becomes progressively older as it moves away from them, with oldest oceanic crust about 180 million years old.

Sediments and life: Seafloor sediments consist of terrigenous material mixed with biogenic oozes produced by microscopic organisms such as foraminifera and diatoms, plus manganese nodules and clay. The biosphere includes ecosystems at hydrothermal vents and cold seeps that rely on chemosynthesis rather than photosynthesis.

Exploration and significance: The seafloor is mapped with sonar-based bathymetry and explored using remotely operated vehicles and submersibles. Understanding the ocean floor informs plate tectonics, ocean circulation, and climate, and holds potential resources such as hydrocarbons, minerals, and methane hydrates, while deep-sea environments are sensitive to disturbance.