I Didn’t Know That...

Q: Why are our oceans salt water, but our lakes and rivers fresh water? What happens to the salt when ocean water evaporates?

A: The Earth’s water supply goes through a complex cycle of evaporation and precipitation called the hydrogeological cycle. Pure water evaporates from the ocean, leaving behind any dissolved minerals. You might notice the same phenomenon in a teakettle, where a crust of minerals is left behind when hot water evaporates. The pure water falls on land, collecting in rivers and lakes. As it flows toward the ocean, it picks up small amounts of minerals and carries them along. When the water evaporates from the ocean, it leaves the minerals behind. When this process is repeated over millions or billions of years, the ocean develops a high mineral content. One of the most common minerals carried into the ocean by rivers is salt, so ocean water is salty. A similar process has occurred in the Great Salt Lake because there is no outlet for water other than evaporation.