These vast bodies of water surrounding the continents are critical to humankind. But overfishing and global warming threaten to leave this vital habitat barren.

The ocean is a continuous body of saltwater that covers more than 70 percent of the Earth's surface. Ocean currents govern the world's weather and churn a kaleidoscope of life. Humans depend on these teeming waters for comfort and survival, but global warming and overfishing threaten to leave the ocean agitated and empty.

Geographers divide the ocean into four major sections: the Pacific, Atlantic, Indian, and Arctic. Smaller ocean regions are called seas, gulfs, and bays, such as the Mediterranean Sea, Gulf of Mexico, and the Bay of Bengal. Stand-alone bodies of saltwater like the Caspian Sea and