The hydrosphere is the combined mass of water found on Earth. A planet's hydrosphere can be liquid, vapor, or ice.

The Great Pacific garbage patch, also described as the Pacific trash vortex, is characterized by exceptionally high concentrations of plastic, chemical sludge, wood pulp, and other debris trapped by the currents of the North Pacific Gyre.

As so much of the Earth's surface is underwater, it comes as no surprise that marine species outnumber those on land. An incredible 94 percent of the Earth's living species exist within the oceans.

Of the five ocean basins, the Atlantic Ocean is the saltiest. On average, there is a distinct decrease of salinity near the equator and at both poles, although for different reasons.

According to NASA's Jet Propulsion Laboratory, if all the glaciers and sheets of Arctic ice melted at the same time, ocean levels would rise an estimated 262 feet, which is about the height of a 26-story building--just a bit shorter than the Statue of Liberty.

The mesopelagic zone is sometimes referred to as the twilight zone or the midwater zone. The light that penetrates to this depth is extremely faint. It is in this zone that we begin to see the twinkling lights of bioluminescent creatures.

The average depth of the ocean is about 12,100 feet. Since light waves can only penetrate 330 feet of water, most of the ocean exists in absolute darkness.

Prochlorococcus and other ocean phytoplankton are responsible for 70 percent of Earth's oxygen production. However, some scientists believe that phytoplankton levels have declined by 40 percent since 1950 due to ocean warming.

Ocean water gets more dense as temperature goes down. So the colder the water, the more dense it is. Increasing salinity also increases the density of sea water.

With approximately 25,000 islands, the Pacific Ocean has more islands than anywhere else on the planet.