At the same time, the ocean hosts some of the world's oldest creatures: Jellyfish have been around more than half a billion years, horseshoe crabs almost as long. More than 80 percent of the ocean is unmapped and unexplored, which leaves open the question of how many species there are yet to be discovered. Bizarre fish with sensitive eyes, translucent flesh, and bioluminescent lures jutting from their heads lurk about in nearby waters, often surviving by eating bits of organic waste and flesh that rain down from above, or on the animals that feed on those bits.ĭespite regular discoveries about the ocean and its denizens, much remains unknown. These chimney-like structures allow tube worms, clams, mussels, and other organisms to survive not via photosynthesis but chemosynthesis, in which microbes convert chemicals released by the vents into energy. But then hydrothermal vents were discovered. The deepest reaches of the ocean were once thought to be devoid of life, since no light penetrates beyond 1,000 meters (3,300 feet). Other fodder for sea dwellers includes seaweed and kelp, which are types of algae, and seagrasses, which grow in shallower areas where they can catch sunlight. Life in the ocean depends on phytoplankton, mostly microscopic organisms that float at the surface and, through photosynthesis, produce about half of the world's oxygen. Fish, octopuses, squid, eels, dolphins, and whales swim the open waters while crabs, octopuses, starfish, oysters, and snails crawl and scoot along the ocean bottom. The oceans are home to millions of Earth's plants and animals-from tiny single-celled organisms to the gargantuan blue whale, the planet's largest living animal. This conveyor belt of heat drives global weather patterns and helps regulate temperatures on land, acting as a heater in the winter and an air conditioner in the summer.
The oceans absorb the sun's heat, transferring it to the atmosphere and distributing it around the world. Seawater's weight is about 3.5 percent dissolved salt oceans are also rich in chlorine, magnesium, and calcium. The oceans hold about 321 million cubic miles (1.34 billion cubic kilometers) of water, which is roughly 97 percent of Earth's water supply. Inland bodies of saltwater such as the Caspian Sea and the Great Salt Lake are distinct from the world's oceans. Smaller ocean regions such as the Mediterranean Sea, Gulf of Mexico, and the Bay of Bengal are called seas, gulfs, and bays. Geographers divide the ocean into five major basins: the Pacific, Atlantic, Indian, Arctic, and Southern. Humans depend on these teeming waters for comfort and survival, but global warming and overfishing threaten Earth's largest habitat. Ocean currents govern the world's weather and churn a kaleidoscope of life.
The ocean is a continuous body of salt water that covers more than 70 percent of the Earth's surface.
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