Dear children and respected adults! I welcome you all to the “Projects” section. Our research work today is devoted to an interesting topic: why is there salty water in the sea? Have you ever wondered? Do your moms and dads know the answer to this question?
I’ll tell you a secret that even scientists are not ready to convincingly explain what determines the presence of salt in the waters of the World Ocean. Everyone knows that it is salty, but no one has yet been able to prove the fact of the presence of salt 100%. That is why the relevance of the issue does not disappear, and researchers again and again try to come to a single solution, putting forward different versions.
This information will help prepare a project on the subject “The World Around us” for children who have entered 1st grade. Read carefully and draw your own conclusions.
Do you want tales about salt water?
People have long been interested in the question of how salt settled in the ocean. Trying to explain this phenomenon, they began to come up with various legends.
Thus, the inhabitants of Norway used to believe that there was a large mill on the seabed that ground salt all day long. The peoples of Karelia, Japan and the Philippines believed in this version. Only in each country these mills appeared in the ocean in different ways.
But the inhabitants of Crimea believed that the Black Sea water was salty because girls lived at the bottom, who were caught in Neptune’s net and remained imprisoned by the owner of the seas forever. They wove white lace for the waves of the sea and constantly cried for the earth. From their tears the Black Sea became bitter and salty.
Modern science has not believed in myths and legends for a long time and is trying to explain everything with the help of research and scientific facts. Today, there are several theories about the appearance of salt in the waters of the World Ocean.
What is it really like? The first version, but not the only one
This hypothesis explains the salinity of the seas and oceans by the water cycle in nature.
Falling rains gradually wash out and dissolve mineral salts in the soil, and streams and rivers, with their currents, carry all impurities into the seas and oceans. The sun heats the sea surface, causing water to evaporate. What about salt? It doesn’t go anywhere, but remains on the seabed.
This is interesting! Try to find out how the water cycle works experimentally. To do this, dissolve sea salt in a small amount of water and keep the container with the resulting mixture on the fire until all the water has evaporated. What will you see at the bottom? That's right, there will be salt left there!
The water that has evaporated from the sea surfaces again falls to the ground and, together with the rain, repeats its path, collecting new salt and other impurities along the way. According to scientists, this salinization of the waters of the World Ocean has been going on for more than two billion years. Therefore, according to the first hypothesis, the process of salt appearance is slow and gradual.
However, those who do not believe in such a theory have a question: if rivers and streams have been bringing salt to sea waters for so long, why has the percentage of this substance not changed over such a long period? Today (as much before) it is about 35 grams per liter.
Causes of salinity of seas and oceans
There are two theories about why seawater 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.
Interesting to know: what oceans 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 .
Or maybe there are other reasons? Version two, no less interesting
Some researchers believe that the water in the seas and oceans was salty from the very beginning, and the rivers had nothing to do with it. The thing is that during the formation of the earth’s crust of our planet, active volcanoes emitted gases full of various vapors from their craters. They poured out acid rain and formed the first acidic seas on Earth.
The acidic seawater reacted with the hard rocks of the seabed. As a result of such chemical processes under the influence of magnesium, sodium and calcium, salts appeared that neutralized the acid in sea water.
The volcanoes gradually subsided, acid rain became less and less every thousand years, and the chemical composition in the seas “settled down.” About 500 million years ago, the world's oceans became salty once and for all.
Data. The salt content in sea water is seventy times higher than in river water.
Version three, final: animals are to blame for everything
There are also scientists who believe that previously the water in rivers and oceans was no different. It was salty everywhere. Why then are the rivers now fresh?
The third hypothesis is inclined to believe that animals that came to the river banks to drink were responsible for the desalination of river water.
They drew calcium from river waters, which is necessary to maintain the skeletal functions of living organisms. They also took salt from the rivers. Since the process took place over millions of years, there were almost no salt reserves left in the rivers.
If the two previous versions probably have a right to exist, then the third can hardly justify our question. Think for yourself, this is how much salt the poor animals need to eat! After all, if all its reserves are distributed on the earth’s surface, the thickness of the layer will be about one hundred meters! And why then did they drink only from rivers and not quench their thirst with the waters of the seas and oceans? Strange? I think more than that!
Animals are also credited with changing the chemical composition not in river water, but in sea water. For their growth and development, multiplying living creatures took only calcium and some carbonates from the surrounding aquatic environment, and they did not like salt. That is why the mineral remained in such concentration. But this version is not particularly supported either.
Otherwise, the percentage of salt content in the World Ocean would already go off scale.
Do you know that?! The Gulf of Finland in the Baltic Sea is the least salty, but it will be easy to swim and float on the surface of the water in the Red Sea due to the high concentration of salt in it. Those who can’t swim at all don’t have to worry about going to the Dead Sea. The water there is so salty that even marine inhabitants cannot live, but drowning is almost impossible.
Why is the sea salty?
Why is the sea salty? Why does a hedgehog need needles? Why did they add “-s” to many words in the last century? Why do cats purr and what do they do? Is it possible to create a time machine according to the laws of physics? As a parent or teacher of primary and secondary schools, you will hear these questions more than once. We will be happy to answer them.
Why is the sea salty?
The answer to this question must begin with an explanation of where the water in the sea and ocean comes from.
In rivers we find springs and springs - underground springs, but where does the water, and salty one, come from in the sea? The reserves of both the Black Sea and the Atlantic Ocean are replenished with fresh water from rivers and precipitation in the form of snow or rain. Both consist of fresh water (in fact, also salty, just in a very small concentration). But unlike rivers, water from oceans and seas does not flow anywhere, but only evaporates when exposed to the sun’s rays. When evaporation occurs, the salts remain.
Another factor in the salinity of the sea is the movement of the rivers themselves flowing into it. On the way to the seas and oceans, river flows wash the salts that make up the stone out of the rocks and bring them with them to the sea, albeit in small quantities.
It turns out that the sea has become salty? Was it fresh before that? No, that's not true. The main reason, which modern scientists agree with, is the process of formation of the sea itself, which was just as salty millions of years ago. The fault for this is not the rivers, which did not exist then, but the volcanoes that covered our planet.
The water of the primary ocean was formed from volcanic gases, the composition of which is approximately the following: 75% of water accounts for 15% carbon dioxide and about 10% of various chemical compounds. These compounds include methane, ammonia, sulfur, chlorine and bromine, as well as various gases. So when the products of the eruption fell to the ground in the form of acid rain, they reacted with the bottom of the future sea, and as a result we got a salty solution.
How much salt is there in the sea?
About 35 grams of salt are dissolved in one liter of sea water .
How much water is there in the sea?
If we take the average depth of the world's oceans to be 3703 meters, and take the average surface area to be 361.3 million square kilometers, we get 1.338 billion km 3
Which seas are the freshest and saltiest?
Let's start with another record holder - the largest sea. The absolute champion in this category is the Sargasso Sea, which is located inside the Atlantic Ocean. Its area reaches 8.5 million square kilometers.
But the freshest sea is in Russia, and this sea is the Baltic. Compared to the waters of the Atlantic, its sunshine is 5 times lower. Why? About 250 rivers flow into the Baltic Sea, which “desalinize” the waters.
What about the saltiest sea?
The record holder for the percentage of salts is the Red Sea. Its salinity is about 41 grams per liter of water! This phenomenal content explains the unique properties of the sea: it is very easy to float in it, and being in it itself is quite beneficial for health.
Why is the Red Sea so salty? The point is the fumes, which we wrote about at the very beginning. Water evaporates from this sea at a tremendous speed due to high temperature and low humidity, so that rains simply do not have time to “desalinate” it, and besides, very little of it falls.
Question - competition
Using the data above, calculate how much TOTAL salt is dissolved in ALL the seawater on our planet?
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