Random Science

Why is the sea salty?

All water on our planet, from rainwater, water in lakes, sea water … contains chemical compounds that scientists call “salt”. However, among them only seawater is always salty, while other types of water are not. Why is there such a difference, let’s find out through the article below.

Origin of the ocean

On Earth includes 5 oceans including: Pacific, Atlantic, Indian Ocean, Arctic Ocean and Antarctic waters. Scientists predict that based on ancient fossils found on the sea floor, the ocean is more than 500 million years old.

The ocean is more than 500 million years old

Regarding the origin of the stepfather, many scientists have come up with different theories but no hypothesis can fully explain all aspects of the problem.

Among them, the hypothesis that both the atmosphere and the ocean are gradually accumulated from the time of geological tectonics through the “gas” process of the Earth has received the most agreement from scientists. .

According to this theory, water vapor and other gases emitted from the molten magma of the Earth after ascending, are cooled to cloud cover above. As the Earth cooled below the boiling point of water, rain began to appear and continued continuously for the next several centuries. This rainfall covers most of the Earth’s surface, and creates the first primary ocean. At this time, thanks to gravity, water is retained, not falling off the Earth.

Origin of salt

Seawater is a complex mixture of compounds from decomposing marine organisms and mineral salts. The magma on the Earth’s crust is cooled by weathering and erosion. When the mountain was formed, minerals from the mainland were swept away by rainwater and streams to the sea and accumulated gradually in large amounts today.

Rocks and sediments beneath the sea floor also contribute to the creation of some salts in the ocean. In addition, salt in the ocean comes from the solids and gases inside the Earth’s escape through volcanic vents in the ocean.

A large amount of fresh water flows from the rivers to the sea, so why is it not diluted by fresh water?

Day and night, huge amounts of fresh water from major rivers in the world such as the Amazon, Mississippi, Mekong, … are always pouring into the Pacific, Atlantic … So why is the sea still salty without being made? dilute? The reason is that salt is only one of the factors responsible for the saltiness of the ocean.

The ancient sea contained only a small amount of salt, not as salty as today. But about a hundred million years ago, the stream of water created from the first rains that rained down on the young Earth broke geological layers and dragged minerals into the sea. This makes the sea more salty gradually. It is estimated that each year rivers and streams flowing from the United States bring 225 million tons of dissolved solids and 523 million tons of sediment. If all the rivers on Earth are counted, the amount of mineral salts pouring into the sea each year is up to 4 billion tons.

Let us know that, under the influence of heat from the Sun, the nearly pure water vapor in the sea rises, but the mineral salts remain in the sea. This steam is carried by the winds to other places. Steam will condense when it meets the cold air high up and falls to the ground to form rain. Rainfall on land will gather in streams and rivers and eventually flow into the sea. This fresh water dissolves the amount of salt under the sea, which makes the seawater continue to taste salty. This cycle goes on and on.

Water cycle
Water cycle.

Composition of sea water

After years of research, scientists still cannot fully understand the chemical composition of seawater. The main reason is due to the size of the ocean, accounting for 70% of the Earth’s surface, the marine environment has an extremely complex system of chemical compounds, some of which are constantly changing. according to the cycle of time.

Composition of sea water
Composition of sea water.

Currently, scientists have only discovered 72 chemical elements in seawater, a number too small compared to the amount of compounds actually exist in the ocean. Some scientists believe that, in seawater, there exist all the natural chemical elements of the Earth, even these elements combine together in both dissolved forms, or precipitate into sediment. deposited on the sea floor. Even when precipitated, under the influence of continuous processes in the marine environment these compounds are still capable of changing their chemical composition.

How salty is the sea?

According to estimates by chemists, there are more than 50 million tons of dissolved substances in the oceans on Earth. If salt can be separated in seawater and brought to the ground and spread evenly across continents, it will create a layer up to 152m thick, equivalent to a 40-storey building today.

In 28 liters of seawater contains about 1kg of salt, according to the researchers’ calculations, the seawater is about 220 times more saline than the freshwater in the lake.

In 28 liters of seawater contains about 1kg of salt

However, the salinity of seawater varies in different regions of the Earth, it depends on factors such as evaporation level, buying volume, melting level, amount of water flowing from rivers, streams, snowfall, wind, wave motion into ocean currents.

The most salty sea water …

The most saline waters belong to the Red Sea and the Persian Gulf region, the two regions with the highest evaporation rate of seawater, with 40 o / oo, the thousandth unit (o / oo) to measure about salinity.

The red sea is the most salty sea in the world
The red sea is the most salty sea in the world.

Comparing between the major oceans, the ocean with the highest salinity level of the ocean is the Atlantic Ocean with an average salinity of about 37.9 o / oo. In the North Atlantic Ocean, the Sargasso Sea is the region with the highest salinity because the temperature in this area is quite high and is far from the mainland so it does not receive fresh water from rivers and streams.

Seawater has the lowest salinity medicine in the Arctic and Antarctic sea areas, 2 regions have low temperatures, continuous rain and melting ice.

The coastal bays such as the Baltic Sea (salinity from 5 to 15 o / oo), Black Sea (salinity below 20 o / oo) … have lower salinity than the average because of the addition of water New sweet volume several billion tons per day.

The salinity of the waters along the coast of countries also varies by geographic location and time of year.

In general, the average salinity of seawater on the whole Earth is about 35 o / oo. This is a result estimated by the scientist William Dittmar in 1884, after analyzing 77 seawater samples in different parts of the world.

Resulting composition of 77 seawater samples.

Resulting composition of 77 seawater samples

How is the composition of river water and seawater different?

The analysis of William Dittmar shows that seawater consists of many different compounds. In which, sodium and chlorine (combined with NaCl) are the main factors that make up the salty taste of seawater, accounting for 85% of the dissolved substance in seawater. In the ocean, 46 times more chlorine than calcium.

In the river water contains a number of silicates and iron compounds, in seawater there is no. In addition, 50% of the dissolved solids contained in river water are Calcium Bicarbonate compound, 2% less than seawater.

The proportion of the main components of seawater is almost constant, NaCl, Magnesium, Sulfate, Calcium and Potassium account for 99% of the water-soluble solid compounds although salinity and total salt content inside the seawater are different. each other around the world.

As for other uncommon elements such as aluminum, copper, tin, … dissolved gases such as Oxygen, CO2, and Nitrogen, the ratios differ among different waters.


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