Naked Science Forum

Life Sciences => The Environment => Topic started by: stana on 14/12/2007 19:31:40

Title: How did all the salt get there in the first place?
Post by: stana on 14/12/2007 19:31:40

Hey guys. How did salt get into the sea in the first place?

The dead sea has alot more salt in than other seas, how is this?

another question, is it actual salt we can buy from the store? Table salt?

Title: How did all the salt get there in the first place?
Post by: another_someone on 15/12/2007 02:12:59

 The Dead Sea !...a few questions ? (http://www.thenakedscientists.com/forum/index.php?topic=10777.0)
 Salt Water & Fresh Water...they're the main two eh ? (http://www.thenakedscientists.com/forum/index.php?topic=9629.msg118109#msg118109)

Title: How did all the salt get there in the first place?
Post by: opus on 20/12/2007 19:21:16

As I understand it, salts are washed out of rocks and soils and are carried by streams and rivers as they flow towards the sea, which is where they end up. These salts stay behind when water evaporates. Some then become part of new rocks and soils beneath and at the edge of these bodies of water so the saltiness of the sea stays roughly the same- although the Dead Sea obviously has more than its share of available salt-maybe its surrounding rocks contain more....?

Title: How did all the salt get there in the first place?
Post by: stana on 21/12/2007 17:25:42

aaah i get it now. Thanks!!

Title: How did all the salt get there in the first place?
Post by: damocles on 22/06/2011 16:23:31

The actual story of the salt in the sea and on land is quite a remarkable one. Surprisingly, it involves the chemistry of the atmosphere!

Bascially, there are two questions:
(1) if the rivers are continually washing salt to the sea, why isn't the sea getting saltier and saltier?
(2) why are many salt lakes much saltier than the sea?

There is a third, hidden question:
(3) why are most desert soils quite salty?

We know that when saltwater evaporates, the water becomes vapour, and it leaves the salt behind.
We can easily determine, by measuring salt levels in rivers, that more salt is continually being brought into the ocean.
The salt must therefore be getting recycled somehow. Moving through the land is not a realistic possibility. We know that geological processes move land around, but they are much too slow to keep up with the amount of salt recycling. That leaves moving through the air with the winds as the only possible option for salt recycling.

Salt does not evaporate with ocean water. Instead, it gets into the atmosphere in stormy weather. Choppy waves make splashes. But the splashes are large droplets of water that quickly fall back near where they were made. But waves also make bubbles under the water, When these bubbles come to the surface and burst, they cause absolutely tiny droplets of water to get thrown into the air. These droplets are so small (sub-microscopic) that their natural rate of falling is only a few centimetres per hour. And the speed and form of storm winds can easily carry them very high very quickly. The water content of the tiny droplets  can evaporate fully or partly, leaving even smaller particles.  The air, all around the world, at all heights, contains some of these tiny salt particles, usually called halites. If it were not for the presence of these halites, it would be very difficult for clouds to form.

There are basically three things that can eventually happen to halites. They can be dry deposited on land. If it rains, they will be washed into rivers and be taken back to the oceans. If not, they will accumulate, and help produce the typical saltiness of a desert soil. They can be deposited directly back into the ocean. No interesting story there. Or they can be incorporated into clouds. They make condensation nuclei, which can allow clouds to grow by adding just one water molecule at a time. If it were not for halites and other nucleating particles, water droplets or ice crystals for clouds could only form if about 1000 water molecules decided to meet at the same place at the same time -- a huge co-incidence.

The eventual fate of these particular halites is to come down with rain or snow when and where the cloud eventually precipitates. And thus they again find their way into rivers and back to the ocean.

Salty inland lakes? Well, lakes of this sort are less subject to the formation of halites, because smaller bodies of water have smaller waves, which produce fewer bubbles when they get choppy. So recycling is much less efficient for these bodies of water, and they accumulate a lot of salt from run-in. Similar story to the salty desert soils.

Title: How did all the salt get there in the first place?
Post by: CliffordK on 23/06/2011 01:19:49

Quote from: stana on 14/12/2007 19:31:40

another question, is it actual salt we can buy from the store? Table salt?

A "Salt" is any compound that forms ionic bonds, and is widely varied.

Your typical table salt is a Sodium Chloride (NaCl) salt, perhaps with iodine added to it.  However, you can also purchase No Salt which is Potassium Chloride (KCl).

You can certainly purchase sea salt for use at the dinner table.  And, if you taste sea water, it will taste salty.

However, it would be best to consider the salt water as a mix of many different ions.  Here is a list of elements in sea water.

http://www.seafriends.org.nz/oceano/seawater.htm

And another list with only the top 11 ions.

http://www.marinebio.net/marinescience/02ocean/swcomposition.htm