So before we can learn about what makes oceans special, let's learn where Earth's oceans are located. Earth has five oceans in all. The first is actually the Arctic Ocean, which is located right up here. Next, we have the Atlantic ocean right here.
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And the Atlantic is one of the oceans that borders the United States. The other ocean that borders the United States is the Pacific Ocean, which is right here. This is the world's largest ocean. Next is the Indian Ocean, which is located just South of India. Lastly, we have the Southern Ocean, which is located near Antarctica.
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So keep these in mind as we go about our lessons.
Section 4
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TEACHER: The main difference between water from lakes and rivers and water from oceans is that the water in oceans contains salt. Got that right here. But what exactly does that mean? Well, oceans have salt dissolved in them. Let's take a look at this diagram. Ocean water is 96.5% water, which
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is represented right here. The other 3.5% is made up of dissolved salts. 3.5 may not sound like a lot, but a little salt goes a long way. So think about putting salt on your food or accidentally taking a gulp of salt water in the ocean. Here's an example.
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1 kilogram of ocean water is equivalent to slightly more than the amount of liquid in a liter-sized drinking bottle. Now this amount of ocean water contains 35 grams of salt, so if I poured that salt into that water and shook it up, would you want to drink it? I wouldn't. See, some scientists estimate that if we could remove all of the salt in the ocean
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and spread it out over the surface of the Earth, it would create a 500-foot layer around the entire planet. That's as tall as a 40-story building. So most of the salt in the ocean water, it actually comes from rocks and minerals on the land. The minerals that come from rocks move into the ocean. Some of the minerals are used by organisms that live in the ocean, but the unused minerals stay there.
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The amount of salt in the ocean water has increased over time. Look closely at the diagram. Ocean water has other ions besides salt. Ions are atoms and molecules that have a positive or negative charge. In the ocean, you'll find magnesium and calcium and other substances, such as nitrogen and phosphorus. Furthermore, ocean water has dissolved gases in it.
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These include carbon dioxide and oxygen. So now let's learn how the presence of salt affects ocean water. The effects of salt on water-- see, the salt in the water makes salt water different from fresh water. The amount of salt in the ocean varies depending on the location.
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In some areas, salt is more concentrated, which means that there's basically more salt in the water. The concentration of salt within the ocean water is called salinity. It's one of our vocabulary words. The more salt in the water, the higher the salinity. The presence of salt has quite a few effects on ocean water.
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If the salinity in the water is high, it actually increases the water's mass. This means that salt water weighs about 2 and 1/2 percent more than the same volume of fresh water. The increase in mass increases the buoyancy of objects in the water. That means that the objects will float more easily in salt water
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than in fresh water. An egg, for example, will sink in fresh water but will float in salt water. The increase in salinity lowers the freezing point of water. Water has to be a much lower temperature for it to freeze, and that's why roads and driveways are salted in areas with cold winters, just like you're seeing right here. Salting roads lowers the freezing point
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what is this?