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Science fiction author Arthur C. Clarke said, "How inappropriate to call this planet Earth, when clearly it is Ocean." Ocean covers 71 percent of Earth's surface and accounts for more than 95 percent of its life-supporting space. Life on Earth began in the ocean some 3.5 billion years ago, and today the ocean continues to make life on Earth possible. The ocean is a living, salty soup; every spoonful contains life, from the deepest trenches to the coldest frozen seas. In fact, the widest variety of life-forms—80 percent of all life on Earth—is found in the ocean, not on land. When you think of an ecosystem teeming with life, you may think of a rainforest; however, ocean habitats are actually far richer. Oceans also make life possible for land-dwelling plants and animals.
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Oxygen
One reason that the ocean is essential to plants and animals on land is because the tiny ocean plants called phytoplankton take in carbon dioxide from the air and convert it into oxygen during photosynthesis. Those ocean plants produce more than half of Earth's oxygen. In the process, they remove carbon dioxide (one of the greenhouse gases that contributes to global climate change) from the air.
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Climate
In addition to carbon dioxide, oceans absorb something else: heat from the sun. The sun warms ocean waters as they hold onto that energy and redistribute it around the planet, thereby affecting the movement, temperature, and moisture content of air masses over sea and land. If it weren't for the ocean and its heat-absorbing and heat-dissipating abilities, Earth would be unbearably hot during the day and frozen at night. However, thanks to currents, the warm and cold waters move and mix, thus evening out temperatures, oxygenating deep waters, and bringing up nutrients from the ocean depths. Warm or cold, currents are like rivers that flow within the ocean. Winds on surface waters cause surface currents, and temperature and salinity (salt) differences create deep ocean currents.
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You can think of the ocean as an engine that drives our planet's climate systems. Temperature differences between sea and land create winds, and winds move air masses and their weather systems with them. Most of the precipitation that falls comes from evaporated seawater. The rain that falls and the water we use to drink and bathe are all linked to the ocean. The ocean even affects the tilt of the Earth itself: its currents cause the poles to wobble.
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Nourishment
The ocean sustains life in an even more direct way: it helps feed a hungry planet. Fish from the ocean provide the principal source of protein for one-sixth of Earth's people. Sea vegetables are important in the diets of many people and are used to manufacture other products. In addition, the seas are a source of minerals. The ocean feeds, warms, and cools us, brings rain, and gives us oxygen. We could not survive without it.
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