Obtain a quart of ocean water or simulated ocean water made by dissolving 1 ounce of table salt in a quart of water. (If you simulate ocean water, weigh the salt before adding it to the water.) Pour the water into a clean, shallow pan. Allow it to evaporate by placing the pan in the sunlight or by gently heating it over a hot plate. When the water is gone, inspect the residue.

If simulated ocean water is used, weigh the residue to see if the original amount of salt remains. (Note: By weight, ocean water is about 3.5 percent salt.)

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Wash some aquarium sand several times, then set the sand out to dry. When it is dry, mix a teaspoonful of table salt with each 4 cups of dry sand (1 tsp salt to 4 cups sand). Make a simulated inclined river bed with aluminum foil, and pour the sand and salt mixture into the river bed. Place a bowl at one end to catch the river water.

Pour some rain water or distilled water at the top of the river bed. Taste the collected water to see if it contains salt (or set the collected water out to evaporate). You will realize that in a similar way rain water dissolves salts in rocks and soil, carries them from the land by way of rivers, and deposits them in the oceans. Thus, the oceans now contain materials that have drained off the land for millions of centuries.