Welcome to brain Stuff from how Stuff Works. Hi, brain Stuff, Lauren Vogel bomb here. Anyone who's taken the dunk in the ocean is familiar with the shock and mild sting the water is so salty. To understand why the seas are salty, look no further than the water cycle. Simply put, the water cycle begins when fresh water falls from the sky in the form of rain. It eventually ends up in rivers, lakes, and oceans, where it soon evaporates to
form clouds and repeat the cycle. If you dig a little deeper into each stage of the water cycle, you'll see just how salt gets into the mix. That fresh water that falls as rain isn't on pure. It mixes with the carbon dioxide in the atmosphere on the way down, giving it a slightly acidic quality. Once it reaches the Earth's surface, it travels over land to reach area waterways. As it passes over the land, the acidic nature of the water breaks down rocks, capturing ions within these rocks
and carrying them along to the sea. Roughly. These ions are so idium or chloride, which forms salt when they banned together. Fresh Water that reaches the ocean evaporates to form clouds. However, these sodium, chloride and other ions remain behind, where they accumulate over time to give the sea its characteristic saltiness. Hydrothermal vents on the ocean floor release additional dissolved materials, including more sodium and chloride, further contributing to
the briny nature of the sea. What surprising is just how much the salt from runoff and underwater vents has built up since the oceans formed. Dissolved salts make up three point five percent of the weight of all ocean water, and if you could remove the salt from the sea, it would form a layer five hundred feet that's a hundred and fifty three meters thick over all of Earth's land mass. That's about the height of a forty story building.
One question, though, if these seas get their salinity from runoff, why do lakes remain relatively salt free. For most lakes, water flows both in and out of the lake via rivers and streams. Salt Ions that end up in the water are carried out, keeping the lake fresh. These ions eventually end up in oceans, which serve as a dumping ground of sorts for runoff and the materials it contains.
Bodies of water with no outflow, such as the Dead Sea or the Great Salt Lake in Utah, maintain a level of salinity on par with or higher than that of the ocean. Today's episode was written by Vambi Turner and produced by Tristan McNeil. For more on this and lots of other salty topics, visit our home planet, how Stuff works dot com.