Jul 16, 2020
Earth is unique among the known planets: it has an abundance of water. Other worlds
— including a few moons — have atmospheres, ice, and even oceans, but only Earth
has the right combination to sustain life.
Earth's oceans cover about 70 percent of the planet's surface with an average depth of
2.5 miles (4 kilometers). Fresh water exists in liquid form in lakes and rivers and as
water vapor in the atmosphere, which causes much of Earth's weather.
Earth has multiple layers. The ocean basins and the continents compose the crust, the
outermost layer. Earth's crust is between three and 46 miles (five and 75 km) deep.
The thickest parts are under the continents and the thinnest parts are under the