Nearly seventy-five percent of the Earth is covered with water. This water makes up five large oceans, and many other bodies of water. The five major oceans are the Atlantic, Pacific, Arctic, Indian, and the Southern Oceans.  There are 322 million cubic miles of water in these five oceans.

At one time, people thought the bottom of the ocean was flat and lifeless. More recently, sound equipment technology and robot submarines have allowed people to explore the ocean floor and map it in great detail.

Scientists now know the ocean floor is full of life. It is alive with marine animals, like the octopus and the squid. The ocean is also full of plants, like seaweed.

The Pacific is the largest ocean. It covers more than 63 million square miles, which is over one-third of the Earth’s surface.  

The oceans also include the deepest point on Earth: the Challenger Deep. This point is located in the Marianas Trench in the western Pacific and is 35,818 feet deep.

In most places, the sea rises and then falls twice a day. This phenomenon is called a “tide.” The moon’s gravity causes these tides, by pulling on the earth and the oceans, causing the water to rise on opposite sides of the Earth.

Waves also cause erosion when they crash against bare rock or shores. As waves wear away rocks over thousands of years, cliffs often form along shorelines. Eroded material is thendeposited as sand on beaches or sand bars.

[Source: The Big Book Of Knowledge]