Why is the water in rivers fresh? Why are the seas and oceans salty? Why is the sea salty?

It is known that oceans cover about 70 percent of the Earth's surface, and about 97 percent of all water on the planet is saline - that is, salt water. According to some estimates, salt in the ocean, evenly distributed over the surface of the globe, would form a layer more than 166 meters thick.

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Sea water tastes bitterly salty, but where did all that salt come from? Everyone knows that the water in rain, rivers and even sea ice is fresh. Why are some of the Earth's waters salty and others not?

Causes of salinity of seas and oceans

There are two theories about why sea water is salty that give us the answer.

Theory #1

Rain that falls on the ground contains some carbon dioxide from the surrounding air. This causes rainwater to be slightly acidic due to carbon dioxide. Rain, falling on the ground, physically destroys the rock, and acids do the same chemically, and transport salts and minerals in a dissolved state in the form of ions. The ions in the runoff move into streams and rivers and then into the ocean. Many dissolved ions are used by organisms in the ocean. Others are not consumed and remain for long periods of time, their concentration increasing over time.

Two ions constantly present in seawater are chloride and sodium. They make up more than 90% of all dissolved ions, and the salt concentration (salinity) is about 35 parts per thousand.

As rainwater passes through the soil and percolates through rocks, it dissolves some minerals. This process is called leaching. This is the water we drink. And of course, we don’t feel the salt in it because the concentration is too low. Eventually this water, with a small load of dissolved minerals or salts, reaches river streams and flows into lakes and the ocean. But the annual addition of dissolved salts from rivers is only a small fraction of the total salt in the ocean. The dissolved salts carried by all the world's rivers would equal the amount of salt in the ocean in about 200-300 million years.

Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to rain again to feed rivers, but the salts remain in the ocean. Due to the sheer volume of the oceans, it took hundreds of millions of years for salt levels to reach current levels.

It’s interesting to know: which ones exist on planet Earth?

Theory #2

Rivers are not the only source of dissolved salts. A few years ago, some features were discovered along the crest of oceanic ridges that changed the way we look at how the sea became salty. These features, known as hydrothermal vents, are places on the ocean floor where water seeping into ocean crust rocks gets hot, dissolves some minerals, and flows back into the ocean.

It comes with a large amount of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of ocean water could pass through the oceanic crust in about 10 million years. Thus, this process has a very important effect on salinity. However, the reactions between water and ocean basalt, the rock of the oceanic crust, are not one-way: some of the dissolved salts react with the rock and are removed from the water.

The final process that supplies the ocean with salt is submarine volcanism—the eruption of volcanoes underwater. This is similar to the previous process - reaction with hot rock dissolves some of the mineral components.

Why are the seas salty?

For the same reasons. Most seas are part of the world ocean with interconnected waters.

Why is the Black Sea salty? Although it is connected to the world ocean through straits, the Sea of ​​Marmara and the Mediterranean, ocean waters almost do not enter the waters of the Black Sea, since many large rivers flow into it, such as:

• Danube;
• Dnieper;
• Dniester and others.

Therefore, the level of the Black Sea is 2-3 meters higher than the ocean level, which prevents ocean water from penetrating into its waters. The salinity of this reservoir and other closed seas - such as the Caspian Sea, the Dead Sea - is rather explained by the first theory and the fact that once the boundaries of the oceans were different.

Will the oceans continue to become saltier? Most likely no. In fact, the sea had roughly the same salt content hundreds of millions (if not billions) of years ago. Dissolved salts are removed to form new minerals on the ocean floor, and hydrothermal processes create new salts.

Where water comes into contact with crustal rocks, either on land or in the ocean or oceanic crust, some of the minerals in the rock dissolve and are carried by the water to the ocean. The constant salt content does not change because new minerals are formed on the seabed at the same rate as the salt. Thus, the salt content of the sea is in a steady state.

Benefit for health

The salinity of sea water has been used by healers for centuries to treat various diseases.

From 1905 until the outbreak of World War I in 1914, biologist René Quinton conducted research to prove that seawater was chemically identical to blood. From these experiments, he developed specific techniques and established a viable protocol for therapy, which he called the "Sea Method". Many case histories indicate the effectiveness of its treatment.

Doctor Jean Jarricott (pediatrician) cured hundreds of children. Particularly good success was observed in children suffering from atrepsy and cholera. Back in 1924, he already practiced the oral use of sea water.

1. How to use it.
2. Application by injection and special effect on digestive problems.
3. Physical and chemical characteristics. Therapeutic definitions and principles of use.

Olivier Macé made huge strides in 1924 with the use of injections for difficult pregnancies and for prenatal applications.

In Senegal, Drs H. Loureu and G. Mbakob (1978) successfully treated one hundred children suffering from severe dehydration caused by diarrhea, vomiting and malnutrition using subcutaneous injections and oral administration of marine plasma.

André Passebecq and Jean-Marc Soulier made very detailed scientific observations of the effectiveness of seawater in various applications and advocated its use. Oral dosage as a mineral supplement does not seem to be very important, but regularity to normalize the body's pH, short- and medium-term therapy with a drinking solution invariably brings rapid results.

F. Paya (1997) reported the use of Quinton plasma to regulate the endocrine system in cases of secondary hyperdosteronism. It has also reported excellent success when administered orally in treating fatigue and maintaining performance in athletes. Paya has used either isotonic or hypertonic formulas with children and adults in cases of:

• dehydration;
• asthenia;
• loss of appetite.

The Germans have proven that consuming sea plasma is as effective as subcutaneous injections. In 70% of cases, patients suffering from psoriasis and neurodermatitis showed a significant improvement in their condition. In Canada, it is used as a food additive.

From time to time we come across some questions related to our planet that have not yet been answered. For example, the presence of salt in ocean water. How did she get there?

The scientific basis for the appearance of salt water in the sea was laid by the work of Edmund Halley in 1715. He suggested that salt and other minerals were washed out of the soil and carried to the sea by rivers. Having reached the ocean, the salts remained and gradually concentrated. Halley noted that most lakes that do not have a water connection with the oceans have salt water.

Halley's theory is partly correct. In addition, it should be mentioned that sodium compounds were washed out from the bottom of the oceans in the early stages of their formation. The presence of another salt element, chlorine, is explained by its release (in the form of hydrochloric acid) from the bowels of the Earth during volcanic eruptions. Sodium and chlorine ions gradually became the main components of the salt composition of sea water.

But we don't know if this can explain the presence of SUCH a huge amount of salt in the oceans. If all the oceans were dried up, the remaining salt could be used to build a wall 230 km high and almost 2 km thick. Such a wall could circle the entire globe along the equator.

Or another comparison. The salt of all the dried up oceans is 15 times larger in volume than the entire European continent!

The regular salt we use every day is obtained from seawater, salt springs, or from mining rock salt deposits. Sea water contains 3-3.5% salt. Inland seas, such as the Mediterranean Sea, Red Sea, contain more salt than open seas. The Dead Sea, occupying only 728 square meters. km., contains approximately 10,523,000,000 tons of salt. There is so much salt in it that it is almost impossible to drown in such water, since the density of the water has increased due to the salts.

On average, a liter of sea water contains about 30 g of salt. Rock salt deposits in various parts of the earth were formed many millions of years ago as a result of the evaporation of sea water. To form rock salt, nine-tenths of the volume of sea water must evaporate; It is believed that inland seas were located on the site of modern deposits of this salt. They evaporated faster than new sea water came in - so rock salt deposits appeared.

The main amount of table salt is obtained from rock salt. Usually, mines are laid to salt deposits. Clean water is pumped through the pipes, which dissolves the salt. Through the second pipe this solution rises to the surface.

In Hong Kong, seawater is widely used in toilet flush systems. More than 90% of them use sea water for flushing in order to save fresh water. The practice began in the 1960s and 1970s, when extracting fresh water supplies became difficult for residents of the former British colony.

Sea water can be drunk in small quantities for 5-7 days without harm to health.

Water is one of the most powerful solvents. It is capable of dissolving and destroying any rock on the surface of the earth. Streams of water, streams and drops gradually destroy granite and stones, and leaching of easily soluble components occurs from them. No strong rock can withstand the destructive effects of water. This is a long process, but inevitable. Salts that are washed out of rocks give sea water a bitter-salty taste.

But why is the water in the sea salty and the water in rivers fresh?

There are two hypotheses about this.

Hypothesis one

All impurities dissolved in water are carried by streams and rivers into the seas and oceans. River water is also salty, but it contains 70 times less salts than sea water. Water from the oceans evaporates and returns to the earth in the form of precipitation, and dissolved salts remain in the seas and oceans. The process of “supplying” salts to the seas by rivers has been going on for more than 2 billion years - time sufficient to “salt” the entire World Ocean.

Sea water contains almost all the elements that exist in nature. It contains magnesium, calcium, sulfur, bromine, iodine, fluorine, and small amounts of copper, nickel, tin, uranium, cobalt, silver and gold. Chemists have found about 60 elements in sea water. But most of all sea water contains sodium chloride, or table salt, which is why it is salty.

This hypothesis is supported by the fact that lakes that have no drainage are also salty.

Thus, it turns out that initially the water in the oceans was less salty than it is now.

But this hypothesis does not explain the differences in the chemical composition of sea and river water: chlorides (salts of hydrochloric acid) predominate in the sea, and carbonates (salts of carbonic acid) predominate in rivers.

Hypothesis two

According to this hypothesis, the water in the ocean was initially salty, and it was not the rivers that were to blame, but the volcanoes. Proponents of the second hypothesis believe that during the formation of the earth's crust, when volcanic activity was very high, volcanic gases containing vapors of chlorine, bromine and fluorine rained down as acid rain. Thus, the first seas on Earth were... acidic. By entering into a chemical reaction with hard rocks (basalt, granite), the acidic water of the oceans extracted alkaline elements from the rocks - magnesium, potassium, calcium, sodium. Salts were formed that neutralized sea water - it became less acidic.

As volcanic activity decreased, the atmosphere was cleared of volcanic gases. The composition of ocean water stabilized approximately 500 million years ago - it became salty.

But where do carbonates disappear from river water when they enter the World Ocean? They are used by living organisms - to build shells, skeletons, etc. But they avoid chlorides, which predominate in sea water.

Currently, scientists have agreed that both of these hypotheses have a right to exist, and do not refute, but complement each other.

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?

It is 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, they wash away salts and other substances that rivers carry into the seas (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.

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.