Why do we have salt water?

[random]

Just wondering why all our huge bodies of water are salt water? if you put salt in a glass of water it eventually all settles to the bottom are the oceans slowly doing this? What happened to cause salt water? when water was formed on earth and most of the planet was water was it salt water then?

[insane_alien]

if you put a proportional amount of salt into a glas it will all dissolve(although the anti-caking agents used in table salt usually hang around.)

 

basically, the salt is dissolved by the water from rocks. this is then washed into the oceans and seas where it accumulates because it does not evapourate.

 

the salt in the ocean will not settle out because it is completely dissolved.

 

the only way for the salt to settle out is if it gets far more concentrated, usually be removing the water by evapouration. This is happening in some parts of the world such as the dead sea where the salt concentration has reached saturation so whenever water evapourates from the dead sea some salt is left behind.

 

This is also one method of producing salt for human consumption or other use although most of it is still mined from ancient buried deposits formed from dried up seabeds (ancient seas that underwent the same process the dead sea is undergoing now).

[random]

But why is there so much salt? What part of the world's evolution created it?

[insane_alien]

well, there's a lot of sodium and a lot of chlorine in the universe. sodium and chlorine react easily and form a stable compound. salts pretty common just because there's a lot of it.

[zapatos]

But why is there so much salt? What part of the world's evolution created it?

Water runs over rocks and dissolves the sodium chloride in it, which is eventually carried into the oceans. There is so much salt in the oceans because this process has been going on for millions of years.

[Moontanman]

It should be pointed out that the salts in sea water are recycled by plate tectonics as well, ocean water follows the ocean floor as it is subducted, this ocean water is what makes the subducted rack and debris melt at lower temps allowing magma to form and exit in volcanoes. Subducted rock saturated with sea water is one of the things that allow plate tectonics to work...

[michel123456]

Water runs over rocks and dissolves the sodium chloride in it, which is eventually carried into the oceans. There is so much salt in the oceans because this process has been going on for millions of years.

 

But rivers carry unsalted water, isn't it?

[insane_alien]

But rivers carry unsalted water, isn't it?

 

its more that they have low concentrations of salt.its there, but undetectable to taste. its a slow process but its been happening for millions of years.

[Moontanman]

But rivers carry unsalted water, isn't it?

 

 

Actually no, rivers carry water that is slightly salty, generally not salt enough for us to taste it but salty enough for us to measure it but it varies widely, The Colorado river is very saline, the Amazon is generally very soft, it should be noted there are other chemicals we are talking about besides sodium chloride, everything that makes sea water "sea water" is carried to the sea by erosion.

 

Most people can tell the difference between sea water and water that is just salted to the same concentration with pure sodium chloride. Fish certainly can and pure salt water does not support ocean life...

 

http://en.wikipedia.org/wiki/Seawater

[zapatos]

Right. The average ocean salinity is 35 parts per thousand. Freshwater salinity is usually less than 0.5 parts per thousand.

[michel123456]

from http://en.wikipedia.org/wiki/Fresh_water :

"Out of all the water on Earth, only 2.75 percent is freshwater, including 2.05 percent frozen in glaciers, 0.68 percent as groundwater and 0.0101 percent of it as surface water in lakes and rivers.[4] Freshwater lakes, most notably Lake Baikal in Russia and the Great Lakes in North America, contain seven-eighths of this fresh surface water." Emphasis mine. Is it to believe that from such a small amount we got the salinity of the oceans as it is today ? Especially considering that "Ocean salinity has been stable for billions of years" ? (from your link http://en.wikipedia.org/wiki/Seawater)

Edited October 2, 2010 by michel123456

[insane_alien]

well, the only way salt can get into the river is when its released be erosion of rocks. this is a slow process while the solvation of salt is fast. this means the concentration of salt in the rivers never gets very high.

 

i'm sure that when water was just starting to condense out of the atmosphere in the beginnings of earth that the rivers did indeed run salty but they would quickly turn fresh as the exposed salt was quickly washed down into the newly formed seas and oceans.

[zapatos]

from http://en.wikipedia.org/wiki/Fresh_water :

"Out of all the water on Earth, only 2.75 percent is freshwater, including 2.05 percent frozen in glaciers, 0.68 percent as groundwater and 0.0101 percent of it as surface water in lakes and rivers.[4] Freshwater lakes, most notably Lake Baikal in Russia and the Great Lakes in North America, contain seven-eighths of this fresh surface water." Emphasis mine. Is it to believe that from such a small amount we got the salinity of the oceans as it is today ? Especially considering that "Ocean salinity has been stable for billions of years" ? (from your link http://en.wikipedia.org/wiki/Seawater)

Water runs over rocks and dissolves the sodium chloride in it, which is eventually carried into the oceans. Water evaporates from the oceans (without the high concentration of salt), and falls as rain. The water that fell as rain on land runs over rocks and dissolves the sodium chloride in it...

Repeat millions of times.

 

"Throughout the world, rivers carry an estimated 4 billion tons of dissolved salts to the ocean annually. About the same tonnage of salt from the ocean water probably is deposited as sediment on the ocean bottom, and thus, yearly gains may offset yearly losses. In other words, the oceans today probably have a balanced salt input and outgo."

 

http://www.palomar.edu/oceanography/salty_ocean.htm

[michel123456]

I don't believe it. IMHO oceans were always salty, and rivers never were.

[insane_alien]

well, then thats just your opinion.

 

Fact: rocks contain salt.

 

Fact: this salt is exposed by erosion

 

Fact: this salt will dissolve in ambient water(whether it's groundwater, precipitation or already in the river)

 

Fact: this salty water will then be washed to the sea.

 

Fact: there isn't anywhere else for the salt to go to the oceans are the worlds biggest evapourative concentrators.

 

The reason rivers have such a low level of salt is because of the large influx of freshwater(from rain) compared to the relatively low influx of salt from erosion.

 

anywhere you have a body of water with a long retention time of water(typically one where there are no outflows) you see salty water. this is because any salt washed there has nowhere to go so it accumulates. the excess water can escape via evapouration so you get a concentrating effect.

 

its a simple mass balance.

[D H]

I don't believe it. IMHO oceans were always salty, and rivers never were.

Just curious, is that a "La la la, I can't hear you" I don't believe it, a "that's how god created things" I don't believe it, or just a "I don't see it" I don't believe it?

 

 

well, then thats just your opinion.

Not just his opinion, mark you. From what I could tell with some searching is that the jury is still out on this. That the first oceans were fresh stands to reason given that rainfall is nearly pure water and river outflow has but a rather salinity. That the first oceans were saltier than today's oceans also stands to reason. If the oceans were dried out the resulting salt was spread evenly over the Earth the result would be a 500 foot thick layer of salt. The stuff of the early Earth probably saltier than it is today after 4 billion years of leaching. This would have made paleorivers a lot saltier than the rivers of today. Combine that with the high temperatures of the Hadeon (more evaporation) and a smaller ocean means the first oceans might well have been a lot saltier than those of today. You will find people, and people who study this stuff, espousing both views on the 'net.

 

If I may hazard a guess, the salinity of the first oceans lay somewhere between 0 and 40% (saturation level at 100 C). From what I can see, anything else is pretty much speculation.

 

Fact: there isn't anywhere else for the salt to go to the oceans are the worlds biggest evapourative concentrators.

Not a fact. That fact was once used as the basis for estimating the age of the Earth. The result: 62 million years. Something is awry here, and what is awry is the assumption that there isn't anywhere else for the salt to go. As mentioned earlier, plate tectonics gives an outlet for that salty water. With ocean water salinity about 200 times that of inflowing river water, the outflow rate due to subduction can be quite a bit less than the inflow rate and still maintain a more or less constant salinity.

Edited October 3, 2010 by D H

[zapatos]

I don't believe it. IMHO oceans were always salty, and rivers never were.

Can you expand on this a bit? I'm wondering where you think the salt in the oceans came from. Are you suggesting that water from comets or asteroids was salty? Or that as water formed on the earth that it was formed salty? And if rivers were always fresh and oceans were always salty, did the source of the water for rivers and oceans come from different places?

Edited October 4, 2010 by zapatos

[michel123456]

Can you expand on this a bit? I'm wondering where you think the salt in the oceans came from. Are you suggesting that water from comets or asteroids was salty? Or that as water formed on the earth that it was formed salty? And if rivers were always fresh and oceans were always salty, did the source of the water for rivers and oceans come from different places?

Well I believe if one could answer the question "where the oceans come from?", this one could also answer to the question "where the salt in the oceans came from".

What my opinion is (just my opinion, not a theory):

If you look at a section of the globe, you will notice a succession of layers from the inside to the outside, going from the most dense (the inner core) to the less dense (not the crust, but the atmosphere). IMHO the oceans are simply a layer of less dense material (water) placed at a position governed by gravity. In this view, the oceans are coming from the entire Earth's mass, and as such, they must contain the traces of all sort of dissolved materials.

[Leader Bee]

So from what i've read so far in this thread is that the seas have been getting progressively saltier and saltier as rocks erode. If this is the case, then would it be reasonable to hypothesise that the accumulation of this salt could have led towards an early mass extinction in the seas or would it be more reasonable to assume that the process takes such a long time that random mutations would have kept anything in this environment from extinction?

[michel123456]

So from what i've read so far in this thread is that the seas have been getting progressively saltier and saltier as rocks erode. If this is the case, then would it be reasonable to hypothesise that the accumulation of this salt could have led towards an early mass extinction in the seas or would it be more reasonable to assume that the process takes such a long time that random mutations would have kept anything in this environment from extinction?

 

You forgot to read that "Ocean salinity has been stable for billions of years" (from http://en.wikipedia.org/wiki/Seawater)

[insane_alien]

yes, it'll have been stable for billions of years because it would have reached equilibrium fairly fast as there was more salt available back then as it hadn't beenwashed down. it would likely have taken a few million years to reach that equilibrium however.

[Leader Bee]

Ooops

[D H]

IMHO the oceans are simply a layer of less dense material (water) placed at a position governed by gravity. In this view, the oceans are coming from the entire Earth's mass, and as such, they must contain the traces of all sort of dissolved materials.

That is not how the oceans formed. The first ocean formed somewhere between 400 to 800 million years after the Earth formed. Those first 400 to 800 million years represent a time when the Earth's surface was extremely hot. The oceans could not form until the surface had cooled to below the boiling point.

 

 

The salt that is currently dissolved in the oceans almost certainly was not the result of solution of salt deposits. We see salt deposits in the Earth now because ancient seas that already contained salt dried up and were subsequently buried. We do not see salt deposits on the Moon. We instead see rocks that contain minerals such plagioclase. Sodium chloride, salt, dissolves readily in water. Those sodium bearing minerals in rocks do not. That would suggest that the initial oceans would have been fresh rather than salty.

 

As to why the oceans have had a fairly uniform salinity for the last billion or two years: Because salts are continuously being transported into the oceans by river water, that means that some other process must exist by which salts leave the oceans. That other process is plate tectonics. Those two processes have reached an equilibrium. Not knowing about plate tectonics, scientists of time past used the fact that rivers are constantly bringing salts into the oceans as a way of estimating the age of the Earth. Assuming that salt never does leave the oceans, they came up with an answer of about 60 million years. That means the tectonic processes that withdraw salts from the ocean operate on a similar time scale. That suggests that it probably took no more than 100 million years for the first oceans to become about as salty as they are today.

[michel123456]

 

As to why the oceans have had a fairly uniform salinity for the last billion or two years: Because salts are continuously being transported into the oceans by river water, that means that some other process must exist by which salts leave the oceans. That other process is plate tectonics. Those two processes have reached an equilibrium.

(emphasis mine)

 

In order to reach an equilibrium, those 2 processes must be linked together by some sort of mechanism. Like water evapourating from the oceans is in equilibrium with the water raining from the clouds. What is that mysterious mechanism that connects salt coming from rivers with salt going away by plate tectonics? IMO there is no such mechanism: the explanation is incorrect.

[Moontanman]

(emphasis mine)

 

In order to reach an equilibrium, those 2 processes must be linked together by some sort of mechanism. Like water evapourating from the oceans is in equilibrium with the water raining from the clouds. What is that mysterious mechanism that connects salt coming from rivers with salt going away by plate tectonics? IMO there is no such mechanism: the explanation is incorrect.

 

 

So you are saying there is no plate tectonics? Can you back that up with anything other than your Opinion?