(ITO) The Earth's Ocean Lesson

The Earth's Ocean Lesson

The Origin of the World Ocean

The Earth is believed to be approximately 4.6 billion years old. But the planet that existed then was very different from the planet on which we live today. The Earth was hot and completely dry. When the Earth was first formed, the planet was covered with volcanoes and the air was full of volcanic gases. The volcanoes, the heat from the Earth's interior, and the incoming meteorites made the surface of the planet incredibly hot. In fact, the surface of the planet was so hot that no water could collect there. The Earth's water existed as water vapor and combined with other gases to form thick clouds.

After millions of years, the Earth began to cool and hot rains fell toward the surface. As the Earth continued to cool, more rain fell and the water collected in the basins of the Earth's crust. It is believed that these rains continued for about 20 million years, and as the water fell, water began to dissolve minerals from the rocks. The water also collected ions from the volcanic gas, which contained chlorine. Both the ions and the minerals together helped to create a saltwater ocean. It was in this new ocean that life on Earth first began more than 3.5 billion years ago.

The Ocean Basins

Seventy-one percent (71%) of the Earth's surface is covered by water. And of that 71%, 97% of the water makes up the ocean. That means only 3% of the Earth's water is fresh water. The water on the earth's surface is divided into four separate basins: The Pacific, Atlantic, Indian, and Arctic. Up until recently, these four basins represented Earth's four oceans. However, in 2000, the Southern Ocean was included to make up the Earth's five oceans. This new ocean surrounds Antarctica and extends to 60 degrees latitude. Although the International Hydrographic Organization officially sanctioned the name, there is some continued discussion as to the details of the acceptance of the Southern Ocean as an official body of water. All of the Earth's oceans are connected to form the World Ocean. The World Ocean is the dominant feature of the Earth and most of its living organisms.

Ocean	Area (square miles)	Average Depth (ft)
Pacific Ocean	64,186,000	15,215
Atlantic Ocean	33,420,000	12,881
Indian Ocean	28,350,000	13,002
Southern Ocean	7,848,300	13,100 - 16,400
Arctic Ocean	5,106,000	3,953

Smaller regions of the ocean are called seas, gulfs, or straits. There are several seas present on the Earth. The largest seas are the South China Sea, the Caribbean Sea, and the Mediterranean Sea. Recognizable gulfs are the Gulf of Mexico and the Persian Gulf. Straits are narrow channels of the ocean that connect two larger bodies of water. An example would be the Strait of Dover or the Strait of Gibraltar.

The picture of the ocean basins is illustrated below. The graduation from red to yellow to green to blue indicates increasing depth.

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