Why is the sea salty?

Everyone knows the sea is salty because of the salt. But the salt come from? Almost every culture has a myth to explain the salty starfish. In the scientific sense, the answer is simple: Sea salty thanks to salt produced from rocks on land.

For years, rain has fallen on Earth. In the rain contains dissolved CO ₂ from the atmosphere surrounding the planet, making mild acidic rainwater derived from carbonic acid - made up of CO2 and water. Rain falls on rocks and acids in rainwater decomposing rocks, creating a soluble form of salts (ions). These ions are brought to the oceans by streams and rivers.

According to Galen McKinley, professor of ocean and atmospheric science, UW-Madison University (USA), salinity of seawater comes from dissolved mineral salts, mainly sodium, chloride, sulfur, calcium, magnesium and potassium.

In it, the two most significant ions in seawater are chloride and sodium, accounting for up to 90% of the total dissolved ions in the ocean.

South Pacific Ocean.According to scientists, salty sea is caused by salt ions dissolving from rocks, then following rivers pouring out and accumulating in the oceans.(Photo: Tourism Australia)

A large part of these dissolved ions are consumed by ocean organisms and removed from the water. The rest is accumulated over a very long period of time and their concentration in seawater gradually increases. As a result, the salinity (salt concentration) in the sea is now about 35 parts per thousand. In other words, 3.5% by weight of seawater are soluble salts, and in a cubic mile (about 1,600m ³ ) of seawater there are about 120 million tons of salt.

However, according to Professor McKinley, 'every year, the amount of ions brought to the ocean by the rain only makes available salt which increases at very low rates, only 0.00005%'. According to experts' estimates, if all the salt in the ocean is spread evenly on the ground, one would have a layer of salt up to 166 meters thick, which is the height of a 40-storey building.

According to Professor McKinley, 'there are geological evidence showing that the salinity of seawater has a history of at least 1 billion years'.

But don't think the sea only has salt! In 1,600m ³ of sea water, there are 25 tons of gold and 45 tons of silver!

Quang Thinh