An interconnected system of undersea tectonic spreading centers wrapping itself around the Earth, resembling the seam on a baseball.
The most famous section of the Mid-Ocean Ridge is the Mid-Atlantic Ridge, whose discovery confirmed the theory of plate tectonics.
The Mid-Ocean ridge is also the world's longest mountain range, stretching over 35,000 miles (56,000 kilometers) under the ocean. Most of the world's spreading centers are part of this system:
The northern end of the Mid-Indian Ridge feeds into the Gulf of Aden where it merges with the spreading center under the Red Sea and the East African Rift Valley system.
The northern end of the East Pacific Rise feeds itself into the Gulf of California where it merges with the San Andreas Fault, a long transform fault system dividing the Pacific Plate from the North American Plate. The fault emerges into the Pacific Ocean north of Cape Mendocino in California, where it merges with the Juan de Fuca Ridge. It is unknown if anything happens in the sima between where the Explorer Ridge dives under British Columbia, and where the Gakkel Ridge dives under northen Siberia. But the northeastern section of Siberia is often considered to be part of the North American Plate.