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After completing this page, do the Oceans Quiz

Oceans are the largest bodies of water on the earth. There are four oceans. The largest ocean is the Pacific Ocean. The next largest is the Atlantic, then the Indian and finally the Arctic Ocean.

Oceans together have an area of about 143 million square miles. The average depth of the oceans is two miles, but it can get deeper. The deepest part of the oceans is in the Pacific at the Marianas Trench where it is about seven miles deep. However, oceans are really very thin layers atop the earth compared to the whole earth, sort of like a watery film on a mirror after a hot shower.


Map with ocean labels

Below are some comparisons of the oceans:

Area in Square Miles
Average Depth in feet


How Oceans Formed

About three million years ago, the surface of the earth was soft because the rocks that make it up were quite soft. There could be no oceans because when it rained the water that hit the earth evaporated quickly. Later on, the earth cooled. Its surface was wrinkly like our skin gets when we are in the sun too long. The higher parts of the wrinkles on the earth's surface formed the continents and the deeper parts the earth's oceans. After a while the water stayed put in the deep valleys that formed the oceans' floors.

Today, the floor of the oceans actually looks like mountainous land. At first when one leaves the shore of an ocean area there is a sort of shallow shelf area of water called the continental shelf. It drops off in the continental slopes and finally to the ocean basins or floors which are quite rough and mountainous. Much of this has been formed by underwater volcanoes and their lava.

Within the ocean water itself are several phenomena. One is the ocean currents, which are streams of water within the greater ocean water. They can be cold or warm.

Ocean tides are the rising and falling of water on the ocean shores due to the pull of the moon's and to a lesser extent, the sun's gravity.

Ocean waves are ripples in the ocean or other water forms caused by winds blowing across them.



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