Why are lakes freshwater and oceans saltwater? (Smithsonian.com)
Why are lakes freshwater and oceans saltwater?

It has something to do with this leaky faucet. You see, rain falls on the land as fresh water. As this water flows downward, it ever so slightly erodes the rocks and soil. This causes an ever so slight amount of salt and minerals to dissolve in the water and continue downstream. Eventually, all the dissolved minerals get dumped into the ocean.

Meanwhile water on the ocean's surface evaporates into the air, ditching all those salts and minerals. It then falls back on land as fresh water, replenishes the lakes and rivers, and the cycle continues. In lakes and rivers, theres enough turnover that the water stays fresh. But in the oceans, the salts pretty much stay there for millions of years.

Worldwide, it's estimated that rivers dump about 4 billion tons of salts into the oceans each year. But even with all that new salt, the oceans are so big, that their salinity stays fairly constant, at about 3.5%.

Critical thinking challenge: How is the water cycle like a bicycle?

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Assigned 18 times

  • John0724-YYCA
    6/12/2014 - 01:24 p.m.

    I thought that people just dump salt in to the ocean and that is why the ocean is salty. But because of this article I know how there is salt in this ocean. Ask Smithsonian articles teach me a lot of stuff that I do not know. But this article taught me the most from all the Ask Smithsonian I have read.

  • NildaJimenez
    8/21/2014 - 03:01 p.m.

    if the water is fresh when the rain comes down shouldnt the salt water slowly vanish or turn into freash water. All the rain and stuff.

  • ianw-DiB
    2/11/2015 - 08:41 a.m.

    The water is like a bicycle because you have to learn it the same way you do a bike, like with surfing, boogie boarding, body boarding, skim boarding, etc.