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Speaker 1: Welcome to brain Stuff from how Stuff Works. Hi, brain Stuff,

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Speaker 1: Lauren Vogel bomb here. Anyone who's taken the dunk in

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Speaker 1: the ocean is familiar with the shock and mild sting

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Speaker 1: the water is so salty. To understand why the seas

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Speaker 1: are salty, look no further than the water cycle. Simply put,

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Speaker 1: the water cycle begins when fresh water falls from the

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Speaker 1: sky in the form of rain. It eventually ends up

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Speaker 1: in rivers, lakes, and oceans, where it soon evaporates to

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Speaker 1: form clouds and repeat the cycle. If you dig a

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Speaker 1: little deeper into each stage of the water cycle, you'll

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Speaker 1: see just how salt gets into the mix. That fresh

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Speaker 1: water that falls as rain isn't on pure. It mixes

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Speaker 1: with the carbon dioxide in the atmosphere on the way down,

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Speaker 1: giving it a slightly acidic quality. Once it reaches the

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Speaker 1: Earth's surface, it travels over land to reach area waterways.

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Speaker 1: As it passes over the land, the acidic nature of

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Speaker 1: the water breaks down rocks, capturing ions within these rocks

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Speaker 1: and carrying them along to the sea. Roughly. These ions

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Speaker 1: are so idium or chloride, which forms salt when they

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Speaker 1: banned together. Fresh Water that reaches the ocean evaporates to

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Speaker 1: form clouds. However, these sodium, chloride and other ions remain behind,

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Speaker 1: where they accumulate over time to give the sea its

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Speaker 1: characteristic saltiness. Hydrothermal vents on the ocean floor release additional

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Speaker 1: dissolved materials, including more sodium and chloride, further contributing to

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Speaker 1: the briny nature of the sea. What surprising is just

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Speaker 1: how much the salt from runoff and underwater vents has

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Speaker 1: built up since the oceans formed. Dissolved salts make up

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Speaker 1: three point five percent of the weight of all ocean water,

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Speaker 1: and if you could remove the salt from the sea,

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Speaker 1: it would form a layer five hundred feet that's a

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Speaker 1: hundred and fifty three meters thick over all of Earth's

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Speaker 1: land mass. That's about the height of a forty story building.

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Speaker 1: One question, though, if these seas get their salinity from runoff,

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Speaker 1: why do lakes remain relatively salt free. For most lakes,

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Speaker 1: water flows both in and out of the lake via

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Speaker 1: rivers and streams. Salt Ions that end up in the

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Speaker 1: water are carried out, keeping the lake fresh. These ions

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Speaker 1: eventually end up in oceans, which serve as a dumping

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Speaker 1: ground of sorts for runoff and the materials it contains.

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Speaker 1: Bodies of water with no outflow, such as the Dead

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Speaker 1: Sea or the Great Salt Lake in Utah, maintain a

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Speaker 1: level of salinity on par with or higher than that

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Speaker 1: of the ocean. Today's episode was written by Vambi Turner

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Speaker 1: and produced by Tristan McNeil. For more on this and

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Speaker 1: lots of other salty topics, visit our home planet, how

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Speaker 1: Stuff works dot com.