When Earth was still young, its atmosphere contained a nasty mix of hydrogen bromide, and other noxious emissions from volcanoes. Oceanographers believe that some of these gases dissolved in the primitive ocean, making it salty. Today, however, most of the salt in the oceans comes from the continual rinsing of the Earth. Rain falling on land dissolves the salts in eroding rocks, and these salts are carried down the rivers and out to sea. The salts accumulate in the ocean as water evaporates to form clouds. The oceans are getting saltier every day, but the rate of increase is so slow that it is virtually immeasurable.
|The Dead Sea|
The amount of salts varies in different oceans. There is about 3 per cent in the water of the North Sea and the Atlantic, and up to 4 per cent in the Mediterranean. At the other end of the scale the Baltic has about 1 to 2 per cent. The Dead Sea (photo, above) contains about 25 to 27 per cent of salts. If the oceans dried up, enough salt would be left behind to build a 290 kilometers tall, 1.5 kilometers thick wall around the equator. More than 90% of that salt would be sodium chloride, or ordinary table salt.