Ask Jimmy and the Bug

Jimmy and the Bug
there is a picture of Jimmy with his arms in the air with salty fries.

Hey Bug! Taylor C., Grade 4, wants to know: “Why is the ocean salty?”

Seawater contains lots of dissolved chemicals, including the one you shake over your fries. Sodium chloride—better known as table salt—is the most common of all the chemicals found in the ocean. There are about 35 pounds of it in every 1,000 pounds of seawater. That's enough to cover the entire planet with a layer of salt 500 feet high—as tall as a 50-story skyscraper.

there is a drawing of Bug
There is a picture of Bug a TV with a view of mountains and an ocean.

Where does all the salt in the ocean come from? Nature “weathers” rocks and grinds down mountains, releasing locked-in mineral salts. Rain and melting snow carry these chemicals into rivers and out into the sea. Also, hot water (hydrothermal) vents on ridges in the ocean floor pump chemical-rich water into the sea. Even underwater volcanoes add salt to the ocean.

Freshwater in streams, rivers, and lakes contains salt, too—about one pound in a thousand pounds of water. It doesn't taste salty because the concentration, or amount, of dissolved salt is too low for the taste buds on your tongue to detect. In most lakes, water flows in one end and out the other, keeping the salt concentration low. But salt can build up in lakes if they have no outlets. The Great Salt Lake in Utah is 10 times saltier than the ocean. When water flows into the Great Salt Lake, it can't flow out. Some water escapes by evaporation, but the salt it contained is left behind.

there is a drawing of Bug
there is a picture of Jimmy holding a giant salt shaker.

A little salt goes a long way!

Activity

  1. What is one method of separating salt from water? How does this separate the salt and the water?
    [anno: One method of separating salt from water is to boil the water. Boiling the water causes it to evaporate, and the salt is left behind.]
  2. Imagine you used this method to separate the salt from freshwater. How many pounds of freshwater would you have to treat to get one pound of salt? How many pounds of salt would you get if you used this method for 1,000 pounds of seawater? Answer both questions. Then write a statement comparing the amount of salt in seawater to the amount of salt in freshwater.
    [anno: One thousand pounds of freshwater would have to be boiled to get one pound of salt. If 1,000 pounds of seawater were boiled, it would leave behind 35 pounds of salt. Seawater has 35 times as much salt as freshwater does.]
  3. Where does the salt found in seawater come from?
    [anno: The salt found in seawater comes from rocks that have weathered and released minerals, from hydrothermal vents, and from underwater volcanoes.]
  4. What affects the concentration of salt in a body of water?
    [anno: The concentration of salt in a body of water may be affected by the water's ability to flow both in and out. If water flows in and out of a body of water, such as a lake, the concentration of salt stays low. If water carrying salt flows into but not out of the body of water, then the concentration of salt will increase. Some water may escape by evaporation, but the salt will be left behind.]