What is the longest mountain range on Earth?

The mid-ocean ridge is the longest mountain range on Earth. It is a connected global system of underwater ridges formed where tectonic plates move apart and new oceanic crust rises from the mantle.

Although the name suggests a single ridge in the middle of an ocean, the system winds through the Atlantic, Pacific, Indian, and Arctic oceans. Its connected sections resemble a seam encircling the planet. The continuous mountain system is roughly 65,000 kilometers long, while the full oceanic ridge network is often estimated at about 80,000 kilometers.

Most of the ridge lies beneath the ocean, so it is easy to overlook when comparing it with visible ranges. At spreading centers, magma cools into basalt as plates separate. The Andes are often called the longest continental mountain range, but they are far shorter than the submerged mid-ocean ridge system.