Earth is the only planet with flowing water on the surface. More than two thirds of the Earth's surface is covered by water. It spreads over the surface to an average depth of 2.3 miles (3.7 km). Some parts, called trenches, are much deeper than that. Trenches are underwater canyons. The deepest spot is in the Pacific ocean. It is called the Marianas Trench. This trench is almost 7 miles (11 km) below sea level. This means it is seven times deeper than the Grand Canyon in Arizona!
