BrainStuff Classics: Why Are the Oceans Salty?

Seawater is salty because of several quirks in Earth's water cycle. Learn the reasons why in this classic episode of BrainStuff, based on this article: https://science.howstuffworks.com/environmental/earth/oceanography/why-is-seawater-salty.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,
I'm Lauren vogel Bomb, and today's episode is another classic
from our archive. Today's question is fairly direct. Why are
Earth's oceans and select other bodies of water salty whereas
rivers and most lakes are fresh? Hi brain Stuff, Lauren

(00:24):
vogel Bomb. Here. Anyone who's taken a 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

(00:45):
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 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

(01:07):
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 of these ions are sodium
or chloride, which forms salt when they band together. Fresh
water that reaches the ocean evaporates to form clouds. However,
these sodium, chloride and other ions remain behind, where they

(01:27):
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's 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

(01:47):
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

(02:09):
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

(02:30):
or higher than that of the ocean. Today's episode was
originally produced by Tristan McNeil and is based on the
article why is seawater salty? On how stuff works dot
Com written by Bambi Turner. Brain Stuff is production of
by Heart Radio in partnership with how stuffworks dot Com
and is produced by Tylor Clang. Four more podcasts. My

(02:51):
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