Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 18

Why are most lakes, rivers, ponds, and streams all freshwater, whereas the ocean is salty? Mostly because of the water cycle. Most of the salt in the ocean comes from freshwater rivers and runoff from land. As the water moves over the land and rocks and through the earth, it picks up minute traces of salt and other minerals, which it then carries to and deposits in the ocean.

When water evaporates from the ocean, the salt remains, while the water vapor either precipitates over the ocean or is carried over and deposited as precipitation on land, where it washes more minerals into the ocean. This process “quickly” (that is, on a geological time scale) increased the concentration of salt in seawater to the level at which it is today — on average about 3.5 percent.