Oceans

There are many great mountains on the Earth that have never been explored. These are on the ocean floor.

Suppose you walked out into the ocean. You would be walking on the part of the ocean floor called the continental shelf. Farther away from shore, the shelf suddenly gets very steep. This part of the ocean floor is called the continental slope. The bottom of the ocean floor is called the ocean basin.

Huge mountain ranges run down the centers of the big oceans. These are called mid-ocean ridges. Hot magma comes out of these mountains and forms new Earth crust.

Ocean waves are caused by winds. Waves roll up the continental shelf and splash on the beach.

Ocean tides are the rising and falling of the sea level. Usually, the sea level rises and falls twice a day. At high tide, the water is as high up the beach as it will get. At low tide, the water is as low as it will get.

Tides are caused by the gravity of the moon.

The oceans are big bodies of water. Rivers that run through the ocean are called currents. One important surface current is called the Gulf Stream. It is much warmer than the water around it. Surface currents are caused by winds that blow in one direction. The winds pull the stream of water along with them.

Oceans have undersea currents, too. These are caused by differences in water temperature. Like warm air, warm water rises above cold. The cold water near the poles sinks. The warm water from near the equator rises into the space.

Short Answer Questions

1. Where are you standing when you walk out in the ocean's waves?
2. What causes waves and tides?
3. What causes surface currents and undersea currents?
4. Why does the writer say there are many mountains that have never been explored?
5. Where do most shelves suddenly get steep?

(Keys.)