Click on an underlined word for more information on that subject. An ocean is a vast body of salt water.
Oceans cover more than three-quarters of the surface of the Earth.
The oceans on Earth include the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic Ocean. The ocean floors are composed mostly of basalt . This glassy, lustrous mineral is found in lava flows, and obsidian stones can be massive. Most obsidian is 70 percent silica. Obsidian has a hardness of 5 and a specific gravity of 2.35.