2023-10-05 04:00:04
If there is one experience that we all have already had at a very young age, it is that of drinking from the cup while learning to swim. We therefore notice it very quickly, whether we are in the sea or in a river the taste is very different: salty or not.
Want to take a dip?
Mahmud Hasan. Designpoint3/Shutterstock
The reason is quite simple: we are able to perceive the different concentrations of salt in water. If you take a glass of water and put a little salt in it, you won’t feel it. If you add a little more, you will start to notice the salty taste and so on, just until the water becomes undrinkable. Well if in a liter of sea water, there is on average (The average is a statistical measurement characterizing the elements of a set of…) 35 grammes salt, we find much less in the water of lakes and rivers. So why this difference?
To understand, you have to follow the water cycle. Water is present in the atmosphere in the form of (water) vapor. When this vapor condenses, it forms clouds and precipitation, such as rain or snow. Then the water flows over the surface, infiltrates the ground, interacts with the rocks. Plants use part of it, groundwater stores another, and the rest flows to the sea forming (In intonation, changes in fundamental frequency are perceived as variations in…) rivers, sometimes lakes before continuing under the path.
And when the water reaches the sea, it will spend a little time there. On average, one water molecule passes 3 000 ans in the ocean (An ocean is often defined, in geography, as a vast body of water…) before evaporating and returning to the atmosphere. And the circle is complete.
And the salt in all this?
First, we must answer this first question: what is salt? It is the mixture (A mixture is an association of two or more solid, liquid or gaseous substances…) between two chemical elements, sodium (Na), and chlorine (Cl), which forms sodium chloride (Sodium chloride is a chemical compound with the formula NaCl. It is more called…), NaCl. Where do these elements come from?
There are different gases in the atmosphere, including carbon dioxide (CO2). CO2, this greenhouse gas (The greenhouse effect is a natural process which, for a given absorption of energy…) responsible for global warming (Global warming, also called global warming, or… ), is emitted by volcanoes, for billions of years, and by human activities for over 150 years. In rainwater for example, this gas forms a acid which we call carbonic acid. And when acidified water comes into contact with rocks, it attacks them, it dissolves part of them and removes mineral salts, including sodium. Furthermore, volcanoes also release chlorine, which also falls into rainwater and therefore into rivers.
Water cycle diagram.
Provided by the author
These chemical elements flow to the ocean. Then, when the ocean evaporates, only the water goes into the atmosphere, the sodium and chlorine remain, so the water vapor is not salty. The rain that falls is therefore fresh water.
Thus, lakes and rivers contain a tiny bit of salt, which flows with the water to the ocean. And each time, the rivers bring salt which remains in the ocean, and water which evaporates back into the atmosphere, only to fall back into a river, a lake and so on. This is why the ocean has become much saltier than the waters of rivers and lakes.
All this has been going on since there was liquid water on Earth, or certainly at least 4 billion years ! Little by little, over the course of Earth’s history, sea water has become increasingly salty. Moreover, the residence time of salt in the ocean is 100 million years, compared to 3,000 years for water. How does salt leave the ocean? Sometimes, large quantities of sea water evaporate and salt rocks are formed, such as halite or gypsum, well known to geologists, but also to everyone, since they are sometimes used to salt the roads or as table salt.
It is therefore because evaporation, which is an essential element of the water cycle, leaves salt behind that the latter accumulates in the ocean and that water from continents such as rivers and lakes is soft. Of course, there are exceptions, since there are salt lakes where evaporation is faster than water input from surrounding rivers, such as the Great Salt Lake in the United States. Conversely (In mathematics, the inverse of an element x of a set provided with a law of…) there exist less salty seas, such as the Baltic Sea. Born from the melting of the ice cap which existed 20,000 years ago, this sea was initially a freshwater lake which gradually mixed with sea water.
The history of salt in water is therefore long and complex!
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