A mid-ocean ridge is an underwater mountain range formed by tectonic plates moving apart. As these plates separate, magma rises from the mantle to fill the gap, creating new oceanic crust. This process is known as seafloor spreading and occurs at divergent boundaries. Mid-ocean ridges are the longest mountain ranges on Earth, stretching over 40,000 miles. They are home to unique ecosystems, including hydrothermal vents that support diverse marine life. The most famous mid-ocean ridge is the Mid-Atlantic Ridge, which runs down the center of the Atlantic Ocean.