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The Ocean Ocean Wave
The Immense Ocean
Imagine that you are an ant on Mount Everest. That's about the size relationship of one human being to the ocean.

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Everything about the ocean is immense ? it has the tallest mountains in the world and the deepest valleys. It covers 72 percent of the Earth's surface. That's 139 million square miles or 139 with 19 zeros after it. And it's not just wide. It's deep ? 12,460 feet deep on average. That's 10 Empire State buildings stacked on top of each other!

Ocean
Oceans Alive
Most scientists think life began in the ocean over 3 billion years ago. Today, the ocean contains an amazing array of life at every depth. Over 1 million known species of plants and animals live there, and scientists say there may be as many as 9 million species we haven't discovered yet.

Marine animals come in all kinds of weird shapes, sizes, and colors; and they live in all kinds of different environments within the ocean. Theblue whale, the largest animal in the world, lives in the open ocean, along with millions of tiny drifting organisms calledplankton. In the tropical seas, silverygreat barracudaspursue colorful coral reef fish. Then there's the deep sea ? where it's as dark as night and icy cold. At depths as great as 7,000 feet below the surface,tubewormslive in the most extreme environment in the world ? hot sea vents. There, the water temperature changes from scalding hot to icy cold in the space of a few feet. No matter where you go in the ocean, you will always find life.

Ocean
Gimme Energy
Life in the ocean depends on energy. No animal can move or grow without energy. Most ocean animals get their energy by eating plants or other animals. The connection between organisms based on the transfer of energy is called a food chain or a food web. Most food webs start with the conversion of sunlight into food through a process called photosynthesis. Photosynthesis is an important process that occurs at the surface of the ocean. But deep within the ocean, at hydrothermal vents, food chains are based on the conversion of chemical energy into food. This process is called chemosynthesis.

You've heard of "one world?" Well, technically, all the world's oceans and seas are part of one continuous mass of seawater. But because the ocean is so big, humans have divided it up and named the different parts. There are five oceans and several dozen seas.* Seas are usually smaller than oceans and are partially enclosed by land. But otherwise, they're exactly the same thing.
What's the Difference Between an Ocean and a Sea?
Ocean

* While some scientists claim there are five oceans, others claim there are only four or even three oceans.

 
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Pictures: Warren Balster/Tony Stone | Jeffrey Jeffords |
OAR\National Undersea Research Program (NURP) | NOAA |