That's a mystery - why is the water in the sea salty, but not in rivers and lakes? There is currently no single correct answer to this question, and there are active debates and discussions on this matter in the scientific world.
Scientists only identify two main theories, each of which seems to be correct, but at the same time they contradict each other, and there are several compelling arguments against each.
First theory. The seas and oceans acquired salinity as a result of slow and gradual processes.
So, according to this theory, sea water became salty as a result of the water cycle in nature. This process can be described in more detail as follows: rain gradually washed away and dissolved mineral salts contained in rocks and soils, and rainwater flowed into rivers. Rivers also wash particles of various salts from the bottom, which then fall into the seas and oceans under the influence of the current. Under the influence of the sun's heat, the water over the seas evaporated and fell back to the ground in the form of rain and other precipitation - the process was repeated. And salt, of course, accumulated in the oceans over millions of years, gradually increasing the level of salinity. But here a big question arises: Why has the salinity level of ocean water not increased for more than 500 million years and remained at the same level of 35 ppm (35 grams of salt per 1 liter of water), while the rivers have not stopped supplying mineral elements all this time?
Second theory. Ocean water was salty from the very beginning.
At the initial stages of the formation of our planet, volcanic smoke was emitted from the depths of the mantle along with the first water vapor into the atmosphere. These smokes were enriched with waste products of volcanoes - chlorine, phosphorus and bromine. Water mixing with these vapors looked more like acid than water. Primary acidic water filled the future oceans and seas and destroyed the crystalline rocks of the earth's crust at the bottom, as a result, elements such as potassium, calcium, magnesium, sodium were released... Next, a simple chemical reaction occurred in which chlorine interacted with sodium, and, in fact, it turned out to be salt. Over time, volcanic activity decreased and water salinity levels stabilized.
Both theories do not give an exact answer, but only suggest the possible course of events and processes. We have yet to find out the true reason for this interesting question.
Why is the water in the sea salty? Each of us asked this question at least once in our lives (or, more precisely, in childhood).
"Water wears away stones." This proverb is very true. There is no solvent in the whole world stronger than water. It is capable of eroding salts and acids and easily copes with stones and huge rocks.
Rain streams leach the hardest rocks and wash them into the water. Salt, accumulating in water, makes it bitterly salty.
But why do rivers remain fresh?
Scientists name several reasons. Let's consider the main theories that are offered today by specialists who study sea water.
Why is the water in the sea salty? Theory one.
All impurities that enter the water sooner or later end up in the seas and oceans. Why in the sea? Because rivers are also salty. However, they contain 70% less salt than the ocean. Instruments register it, and the river water tastes fresh. Running water from rivers enters the ocean, and salts accumulate there. The process has been going on for more than two billion years. This time is more than enough to “salt” a huge amount of water. The water gradually evaporates, falls as rain, and returns to the ocean. Salts and other elements remain unchanged: they do not evaporate, but only accumulate.
A good confirmation of this theory are lakes that have no drainage: they are also salty.
For example, (essentially this is a huge drainless lake) contains such an amount of salt that it pushes any body to the surface.
This lake is the lowest point on the planet, which, moreover, is located in a hot place. Due to climate and evaporation, scientists believe, the salinity of the Dead Sea has reached almost 40%. There are no fish or plants in it. Even externally, water resembles an oily substance. And at the bottom of the lake, instead of the usual silt, there is salt.
This theory, which explains why the water in the sea is salty, has one significant drawback. It does not take into account that river water contains mainly sodium chloride (ordinary salt), and sea water contains mainly sodium chloride (ordinary salt).
Why is the water in the sea salty? Theory two.
According to her, initially the water in the ocean was not salty, but acidic. Why? Because during the birth of the Earth, the atmosphere was literally boiling. Volcanoes “threw” many chemical elements into it, and acid rain fell. All this settled on the bottom of the newborn oceans, making it acidic. Gradually, rivers carried eroded rocks into the ocean, which reacted with acid. As a result, salts were released, which made the water salty. Carbonates were also released, but they were and are very actively used by marine animals, which use them to build shells, skeletons, and shells.
A long time ago, the process stabilized, but the water in the seas remained salty. It remains that way today.
Both theories have their place, but neither of them explains exactly why there is different water in the sea and rivers. In some places these hypotheses complement each other, and in others they refute each other.
Perhaps very soon a new theory will appear that will give a comprehensive answer to the question that interests all people on Earth.
Why is the water in the sea salty? There is so much water on the Earth's surface that it is often called the "blue planet." Land occupies only 29% of the Earth's area, and the remaining 70% falls on the mysterious and almost unexplored oceans. Obviously, such a quantity of water cannot have an absolutely identical composition, as can be seen from the example of the different saturation of salts in rivers and seas. But how to explain these differences?
Water is famous for its ability to erode any type of rock. It doesn’t matter what sharpens the stone - a powerful stream or a separate drop - the result is always predictable. During the destruction of the rock, it removes easily soluble components from it. Salts, which are also leached from the stone, give the water its characteristic taste.
Scientists have not been able to come to a consensus as to why some bodies of water have fresh water and others have salt water. To date, two complementary theories have been formulated.
First theory
The first theory is based on the fact that fresh water is just as salty as sea water, but the concentration of salt in it is seventy times lower. Salt-free water can only be obtained in laboratory conditions by distillation, while natural liquids have never been and will not be purified from chemical components and microorganisms.
All impurities that dissolve and are then washed away by water from rivers and streams inevitably end up in the waters of the World Ocean. Then the water evaporates from its surface and turns into, and the salt becomes part of its chemical composition. This cycle has been continuously repeated for two billion years, so it is not surprising that during this time the World Ocean has become so rich in salts.
Proponents of this theory cite salt lakes that have no drainage as evidence. If the water did not initially contain a sufficient amount of sodium chloride, they would be fresh.
Sea water has one unique property: it contains almost all existing chemical elements, including magnesium, calcium, sulfur, nickel, bromine, uranium, gold and silver. Their total number is close to sixty. However, the highest level is due to sodium chloride, also known as table salt, which is responsible for the taste of sea water.
And it was the chemical composition of water that became the stumbling block to this hypothesis. According to research, sea water contains a high percentage of hydrochloric acid salts, while river water contains carbonic acid salts. The question of the reason for such differences still remains open.
Second theory
The second point of view is based on the assumption of the volcanic nature of ocean salts. Scientists believe that the process of formation of the earth's crust was accompanied by increased volcanic activity, as a result of which gases saturated with fluorine, boron and chlorine vapors were transformed into acid rain. From this we can conclude that the first seas on Earth contained a huge percentage of acid.
Under such conditions, living organisms could not originate, but subsequently the acidity of ocean water decreased significantly, and it happened like this: acidic water washed out alkalis from basalt or granite, which were then transformed into salts that neutralized ocean water.
Over time, volcanic activity weakened significantly, and the atmosphere began to gradually clear itself of gases. The composition of sea water also stopped changing and reached a stable state five hundred million years ago.
However, even today the salinity of the water is controlled by a large number of underwater volcanoes. When they begin to erupt, the minerals in the lava mix with the water, raising the overall salt level. But, despite the fact that a new portion of various salts enters the World Ocean every day, its own salinity remains unchanged.
Returning to the question of carbonates disappearing from fresh water when it enters the sea, it is worth adding that these chemicals are actively used by marine organisms to form shells and skeletons.
Everyone knows that sea water is very harmful and tastes unpleasant. However, many adhere to the erroneous ideas that it can easily replace fresh water in conditions of extreme necessity. Such misconceptions can not only harm a person who finds himself in an extreme situation, but also cost him his life.
The thing is that the load associated with filtering any liquid entering the body falls entirely on the kidneys. Their task is to remove excess fluid through urine and sweat. In the case of sea water, the kidneys will have to process a large amount of salts, which can be retained, forming stones and impairing the functioning of the entire body.
Thanks to the kidneys, during the day a person excretes about fifty percent of the liquid he drinks during this period. Instead, excess sodium, calcium and potassium salts leave the body with urine. Sea water is so saturated with salt that the kidneys wear out very quickly, trying to cope with work that is too much for them. One liter of sea water contains thirty-five grams of salt, which is several times higher than its content in human water.
The daily fluid intake for an adult includes not only water, but also moisture received during meals. Every day, from fifteen to thirty-five grams of salt deposits in the body, which the kidneys successfully remove.
Thus, it turns out that in order to get rid of thirty-five grams of salt that entered the body along with a liter of sea water, it will have to produce one and a half liters of its own fluid, taking into account the fact that the amount of water drunk will clearly not be enough for this. To fulfill their task, the kidneys will begin to work to the limit of their capabilities and very quickly fail.
In addition, a lack of fluid coupled with a critical level of salt in the body will lead to severe dehydration, and after a few days the kidneys will stop functioning. Excess salt will cause damage to internal organs, the first of which will be the kidneys and gastrointestinal tract. Due to a lack of moisture, irreversible changes will also occur in the nervous system.
In addition, dehydration in the process of quenching thirst with sea water is caused by the presence of magnesium sulfate in its composition, which has a laxative effect. As a result, dehydration occurs much more rapidly than usual, and the person quickly loses strength and ability to fight for survival.
The body can no longer produce its own fluid and cope with high salt levels. In addition, sea water contains other dangerous substances, on the absorption of which the body will spend its last resources.
However, it is still possible to survive in the absence of fresh water. Some scientists and survival experts advise squeezing the liquid out of fish, no matter how strange it may sound. There are several documented cases where people managed to escape with the help of such fish “juice”.
Thus, the salt contained in the waters of the World Ocean can bring people both the sensation of flight from swaying on the surface of the sea, and become their worst enemy, gradually depriving them of the ocean that is contained in the body of each of us.
Water covers a large area of our planet. The vast majority of this water is part of the seas and oceans, so it is salty and unpleasant to the taste. According to the server "Ocean Service" 3.5% of the oceans are made up of sodium chloride or table salt. This is tons of salt. But where does it come from and, therefore, why is the sea salty?
Important to know!
For 4 billion years, rain waters the earth, rainwater penetrates into the rocks, from where it finds its way into. It carries dissolved salt with it. Over the course of geological history, the salt content of the sea gradually increases. The Baltic Sea, due to low water temperatures, contains 8 times less salt than, for example, the Persian Gulf. If the water from all the oceans evaporated today, the remaining salt would form a coherent layer 75 m high around the world.
Where does the salt in the sea come from?
Yes, some of the salt enters the water directly from the seabed. At the bottom there is a whole series of salt-containing stones, from which salt penetrates into the water. Some of the sodium chloride also comes from volcanic valves. However, according to the BBC, most of the salt comes from the mainland. Therefore, sodium chloride from land is the main reason why the sea is salty.
Each kilogram of sea water contains on average 35 g of salt. Most of this substance (about 85%) is sodium chloride, the well-known kitchen salt. Salts in the seas come from several sources:
- The first source is the weathering of rocks on the mainland; when the stones get wet, salts and other substances that rivers carry into the seas are washed away from them (rocks on the seabed have exactly the same effect);
- Another source is explosions of underwater volcanoes - volcanoes release lava into the water, which reacts with seawater and dissolves certain substances in it.
Water also penetrates into cracks that lie deep on the ocean floor in areas called mid-ocean ridges. The rocks here are hot and there is often lava at the bottom. In the cracks, the water heats up, due to which it dissolves a significant amount of salts from the surrounding rocks, which penetrate into the sea water.
Sodium chloride is the most common salt in seawater because it is the most soluble. Other substances dissolve less well, so there are not so many of them in the seas.
Special cases are calcium and silicon. Rivers bring large amounts of these two elements into the oceans, but despite this, they are scarce in seawater. Calcium is “picked up” by various aquatic animals (corals, gastropods and bivalves) and built into their tanks or skeletons. Silicon, in turn, is used by microscopic algae to create cell walls.
The sun shining on the oceans causes large amounts of sea water to evaporate. However, the evaporated water leaves all the salt behind. This evaporation concentrates the salt in the sea, causing the water to become salty. At the same time, some salt is deposited on the seabed, which maintains the balance of salinity in the water - otherwise, the sea would become saltier every year.
The salinity of water, or the salt content of water, varies depending on the location of the water resource. The least salty seas and oceans are near the north and south poles, where the sun does not shine as strongly and the water does not evaporate. In addition, the salt water is diluted by melting glaciers.
In contrast, the sea near the equator evaporates more due to the elevated temperatures that prevail in this area. This factor not only answers the question of why the sea is salty, but is also responsible for the increased density of water. This process is typical for some large lakes, which become saline during the process. An example is where the water is so salty and dense that people can lie quietly on its surface.
The above factors are the causes of the salinity of sea water, as scientists understand them at the current level of scientific knowledge. However, there are several unresolved issues. It is not clear, for example, why different salts are found throughout the world in essentially the same proportions, although the salinity of individual seas varies significantly.
Are these hypotheses true?
Of course, no hypothesis is completely correct. Sea water has been formed over a very long time, so scientists have no reliable evidence about the reasons for its salinity. Why can all these hypotheses be refuted? Water washes away the land where there is no such high concentration of salt. During geological epochs, the salinity of water changed. The salt content also depends on the specific sea.
Water is different - salt water has different properties. Sea – characterized by a salinity of about 3.5% (1 kg of sea water contains 35 g of salt). Salt water has different densities and freezing points vary. The average density of sea water is 1.025 g/ml, and it freezes at a temperature of -2°C.
The question may sound different. How do we know that sea water is salty? The answer is simple - everyone can easily taste it. Therefore, everyone knows the fact of salinity, but the exact reason for this phenomenon remains a mystery.
Interesting fact! If you visit Sant Carles de la Rápita and go to the bay, you will see white mountains formed from salt extracted from sea water. If mining and trade in salt water are successful, then in the future, hypothetically, the sea risks becoming a “freshwater puddle”...
Double face of salt
There are huge reserves of salt on Earth, which can be extracted from the sea (sea salt) and from mines (rock salt). It has been scientifically proven that table salt (sodium chloride) is a vital substance. Even without precise chemical and medical analyzes and research, it was clear to people from the very beginning that salt was a very valuable, useful and supportive substance that allowed both themselves and animals to survive in the world.
On the other hand, excessive salinity causes a decrease in soil fertility. It prevents plants from getting minerals into their roots. As a result of excessive soil salinity, for example in Australia, desertification is widespread.
Anyone who was on the beach could see that the water in the sea tasted salty. But where does the salt come from if fresh water enters the ocean through rains, rivers, etc.? Why is the sea salty and has it always been like this - time to figure it out!
How is water salinity determined?
Salinity refers to the salt content in water. Most often, salinity is measured in " ppm » (‰). Permille is one thousandth of a number. Let's give an example: a water salinity of 27 ‰ will mean that one liter of water (this is approximately 1000 grams) contains 27 grams of salt.
Water with an average salinity of 0.146 ‰ is considered fresh.
Average The salinity of the World Ocean is 35 ‰. What makes water salty is sodium chloride, also known as table salt. Among other salts, its proportion in sea water is the highest.
The saltiest sea is the Red Sea. Its salinity is 41‰.
Where does salt come from in the seas and oceans?
Scientists still disagree about whether seawater was originally salty or acquired such properties over time. Depending on the versions, different sources of the appearance of salts in the World Ocean are considered.
Rains and rivers
Fresh water always has a small amount of salts, and rainwater is no exception. It always contains traces of dissolved substances that were captured during its passage through the atmosphere. When rainwater gets into the soil, it washes away small amounts of salts and eventually carries them to lakes and seas. From the surface of the latter, water intensively evaporates, falls again in the form of rain and brings new minerals from the land. The sea is salty because all the salts remain in it.
The same principle applies to rivers. Each of them is not completely fresh, but contains small amounts of salts captured on land.
Confirmation of the theory - salt lakes
Proof that salt comes through rivers are the saltiest lakes: the Great Salt Lake and the Dead Sea. Both are about 10 times saltier than seawater. Why are these lakes salty?, while most of the world's lakes are not?
Lakes are usually temporary storage areas for water. Rivers and streams bring water to lakes, and other rivers carry it away from these lakes. That is, water comes in from one end and leaves from the other.
The Great Salt Lake, the Dead Sea and other salt lakes have no outlets. All the water that flows into these lakes leaves only through evaporation. When water evaporates, dissolved salts remain in bodies of water. Thus, some lakes are salty because:
- the rivers carried salt to them;
- the water in the lakes evaporated;
- the salt remained.
Over many years, salt in the lake water has accumulated to its current level.
Interesting fact: The density of salt water in the Dead Sea is so high that it practically pushes a person out, preventing him from sinking.
The same process made the seas salty. Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to fall again as rain and replenish rivers, but the salts remain in the ocean.
Hydrothermal processes
Rivers and rain are not the only source of dissolved salts. Not long ago, they were discovered on the ocean floor hydrothermal vents. They represent places where seawater has seeped into the earth's crust, become hotter, and is now flowing back into the ocean. Along with it comes a large amount of dissolved minerals.
Submarine volcanism
Another source of salts in the oceans is underwater volcanism - volcanic eruption underwater. It is similar to the previous process in that seawater reacts with hot volcanic products and dissolves some of the mineral components.
Will the seas be saltier?
Most likely not. In fact, the sea has had roughly the same salt content for hundreds of millions, if not billions of years. The salt content has reached a steady state. The fact is that part of the salts goes to the formation of mineral rocks at the bottom - this compensates for the influx of new salts.
Resume
There is no mystery in the answer to the question: “Why is the sea salty?” Salt is deposited by rain and rivers, hydrothermal and volcanic processes on the ocean floor.
