Listening practice: The mountain chain beneath the oceans

Imagine a mountain range that begins below the waves, crosses entire ocean basins, and almost never reaches the air. The global mid-ocean ridge system stretches for nearly sixty-five thousand kilometers. More than ninety percent of it lies deep underwater. NOAA Ocean Exploration describes it as the longest and largest mountain range on Earth. At the top of the ridge, the average water depth is about two thousand five hundred meters. So when we picture a mountain range, we should not look only at the continents. A far larger chain is hidden beneath the ocean surface.