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Speaker 1: Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,

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Speaker 1: I'm Lauren vogel Bomb, and today's episode is another classic

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Speaker 1: from our archive. Today's question is fairly direct. Why are

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Speaker 1: Earth's oceans and select other bodies of water salty whereas

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Speaker 1: rivers and most lakes are fresh? Hi brain Stuff, Lauren

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Speaker 1: vogel Bomb. Here. Anyone who's taken a dunk in the

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

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

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

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

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Speaker 1: in the form of rain. It eventually ends up in rivers, lakes,

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Speaker 1: and oceans, where it soon evaporates to form clouds and

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Speaker 1: repeat the cycle. If you dig a little deeper into

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Speaker 1: each stage of the water cycle, you'll see just how

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Speaker 1: salt gets into the mix. That fresh water that falls

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Speaker 1: as rain isn't pure. It mixes with the carbon dioxide

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Speaker 1: in the atmosphere on the way down, giving it a

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Speaker 1: slightly acidic quality. Once it reaches the Earth's surface, it

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Speaker 1: travels over land to reach area waterways. As it passes

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Speaker 1: over the land, the acidic nature of the water breaks

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Speaker 1: down rocks, capturing ions within these rocks and carrying them

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Speaker 1: along to the sea. Roughly of these ions are sodium

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Speaker 1: or chloride, which forms salt when they band together. Fresh

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Speaker 1: water that reaches the ocean evaporates to form clouds. However,

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Speaker 1: these sodium, chloride and other ions remain behind, where they

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Speaker 1: accumulate over time to give the sea its characteristic saltiness.

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Speaker 1: Hydrothermal vents on the ocean floor release additional dissolved materials,

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Speaker 1: including more sodium and chloride, further contributing to the briny

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Speaker 1: nature of the sea. What's surprising is just how much

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Speaker 1: the salt from runoff and underwater vents has built up

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

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

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

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

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Speaker 1: and fifty three meters thick over all of Earth's land mass.

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Speaker 1: That's about the height of a forty story building. One question, though,

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Speaker 1: if these seas get their salinity from runoff, why do

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Speaker 1: lakes remain relatively salt free for most lakes. Water flows

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Speaker 1: both in and out of the lake via rivers and streams.

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Speaker 1: Salt Ions that end up in the water are carried out,

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Speaker 1: keeping the lake fresh. These ions eventually end up in oceans,

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Speaker 1: which serve as a dumping ground of sorts for runoff

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Speaker 1: and the materials it contains. Bodies of water with no outflow,

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Speaker 1: such as the Dead Sea or the Great Salt Lake

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Speaker 1: in Utah, maintain a level of salinity on par with

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Speaker 1: or higher than that of the ocean. Today's episode was

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Speaker 1: originally produced by Tristan McNeil and is based on the

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Speaker 1: article why is seawater salty? On how stuff works dot

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Speaker 1: Com written by Bambi Turner. Brain Stuff is production of

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Speaker 1: by Heart Radio in partnership with how stuffworks dot Com

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Speaker 1: and is produced by Tylor Clang. Four more podcasts. My

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Speaker 1: wherever you listen into your favorite shows