十万个为什么·科学启蒙30篇（3）
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Where Does Salt Come From?
盐是从哪里来的
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Most table salt comes from seawater, underground salt deposits, or ancient dried-up seas.
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Seawater contains about 3.5% dissolved salts, mostly sodium chloride, left behind when water evaporates.
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Salt farms—called salterns—use shallow ponds and sunshine to harvest salt naturally over weeks.
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Rock salt forms when ancient oceans dried up and left thick layers buried deep underground.
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Mines dig these layers out using machines, then crush and purify the salt before packaging.
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Some salt also comes from brine wells, where water is pumped underground to dissolve buried salt beds.
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The resulting salty water is boiled until crystals form, a method used for centuries in China and Europe.
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Iodine is added to most table salt to prevent thyroid problems, especially in children.
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Sea salt often retains trace minerals like magnesium and potassium, giving it a slightly different flavor.
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No matter its source, salt’s chemical formula—NaCl—stays exactly the same.