The Atlantic, the Pacific and the Indian Ocean together cover about 71 percent of the earth's surface. There are an estimated one million species of plants and animals in the world's seas, with just 226,000 of them having been described thus far. And then there are the rising masses of water topped with white foam...

One sport, and even a whole industy, puts oceanic waves front and center: surfing. Many people associate surfing with freedom and vacation. Those who ride the waves, though, say it's not a sport but a way of life. To be a good surfer, you have to take care of your boards, like these two on Waikiki Beach, Hawaii. But even the best board is no good without great waves.

Waves are created by wind blowing over the sea. That generates friction and causes the water to rise up. The stronger and longer the wind blows, the higher the waves get. Once the wind lets up, smooth long waves remain. When they encounter shallow water, they're slowed by the ground. The waves that follow push the water up higher and steeper until the resulting big wave finally breaks.

For those looking for spectacular waves, Hawaii is the place to be. Here, a participant in the Big Wave Awards rides a huge wave off the coast of Maui. Another popular spot is the North Shore of Oahu. Many surfing competitions take place here over the winter months.

Tall waves can also spell danger. Lighthouses like this one on Russia's Black Sea coast are solidly built. But for people with regular beachfront property, the ocean is both friend and foe. Out on the open sea, waves are an average of three meters high (10 feet), but can get much higher in a storm. The biggest tsunami ever recorded hit the coast of Alaska in 1958 and was a whopping 30 meters tall.

There are also many lesser known spots that have great waves for surfers, like Portugal, for instance. Whether a place is good for surfing depends on many factors, among them wind and the strength of the tides. The seafloor is also important. At reefs, waves are breaking fast and steep. On a beach, the location of the wave breaks changes because the sand and thus the shape of the seafloor shifts.

Humans aren't the only ones into riding waves! The US, home to all sorts of crazy dog traditions (see Halloween dog parade), also has canine surf competitions. This participant in the Surf City Surf Dog Contest in Huntington Beach, California, wiped out - but fortunately, dogs are good swimmers and can make it back to shore.