1. Mid-ocean ridges: These are underwater mountain ranges that run for thousands of kilometers along the ocean floor. They are the sites of seafloor spreading, where new oceanic crust is created.
2. Ocean trenches: These are deep, narrow depressions in the ocean floor that are often found near the edges of continents. They are formed by the collision of tectonic plates.
Before the invention of sonar, the ocean floor was largely unexplored, and scientists had no idea that these massive features existed. Sonar allowed scientists to "see" the ocean floor for the first time and revolutionized our understanding of the Earth's geology.
