There are three kinds of plate tectonic boundary, and the mid-ocean ridge is the Earth's most extensive mountain chain

Background

There are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries. At a divergent boundary two plates move away from each other; molten rock rises from the mantle and solidifies to create new oceanic crust. At a convergent boundary two plates come together, and the edges may buckle up into mountain ranges or one plate may bend down into a deep seafloor trench. At a transform boundary two plates slide past each other. The mid-ocean ridge is the most extensive chain of mountains on Earth, stretching nearly 65,000 kilometers (40,390 miles), with more than 90 percent of the mountain range lying in the deep ocean. Mid-ocean ridges occur along divergent plate boundaries, where new ocean floor is created as the plates spread apart.