Sea water is salty. Why? How?

Oceans make up 70% of the Earth’s surface.  The oceans were formed 4.5 billion years ago on the earth. About 97 percent of water on the Earth is saline. When the Earth was formed, its interior released salt ions due to volcanic activities. These salt ions reached the oceans through rainfall and land runoff.

Seawater is a mixture of various salts and water. Most of the water in the ocean basins is believed to have originated from the condensation of water found in the early atmosphere as the Earth cooled after its formation. The following salts are present in sea water. They are: Chlorides, bicarbonates, bromides and sulphates of Sodium, calcium, potassium and magnesium.

Seawater also contains small amounts of dissolved gases. Many of these gases are added to seawater from the atmosphere through the constant stirring of the sea surface by wind and waves. Some of the important atmospheric gases found in seawater include: nitrogen, oxygen, carbon dioxide (in the form of bicarbonate HCO₃), argon, helium, and neon. Compared to the other atmospheric gases, the amount of carbon dioxide dissolved in the seawater is unusually large.

Rain is the chief source of water. It is the purest form of water. Soon after the Earth was formed, the volcanic activity was going on in its interior. Large quantities of gases and steam came out and settled as clouds in the sky of the earth. Afterwards there was huge rainfall for years. Rainwater was collected in low-lying areas and formed water bodies. The earliest rain water was salty because gases like hydrogen chloride, sulphur di oxide emitted by volcanoes had dissolved in it. These water bodies are known as oceans and seas.

The earliest rainfall also dissolved salts on the ground. Although rocks and stones remained almost unaffected, but their soluble salts (e.g. sodium and magnesium) continued to dissolve in rain and went on increasing the salinity of sea water year after year.

Weathering of rocks increases the salinity of sea and ocean water. Weathering is the breakdown of rocks at the Earth’s surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material. That means weathering means breaking down and loosening the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice. Minerals of rocks are deposited in the rivers and lakes and then to the seas and oceans where these minerals increase the salinity of the seas.

When rain falls from the clouds, the rain water has to travel down several layers of the atmosphere before reaching the soil. The rain water mixes with Carbon- di-oxide Sulphur-di- oxide, Hydrogen Sulphide and Nitrous oxide in various levels of the atmosphere. When the rain water reaches the soil, it enriches the soil with carbonates, sulphates and nitrates. Due to soil erosion, the mineral rich top soil is carried away by rain, air etc. to the rivers and then to the seas. Rain also an agent that increases the salinity of sea water.

During summer the sea water evaporates due to sun’s heat. The dissolved salts present in the sea and ocean remain there only. Weathering and denudation of rocks, deposition of minerals by the rivers into the seas and oceans, Evaporation of sea water due’s sun’s heat are going on since ages in nature. So the water of the seas and oceans is salty.

In addition to this, seas and oceans are natural habitats for several living organisms ranging from unicellular amoebae, bacteria to multicellular whales and dolphins. In this marine ecosystem there are several plants and weeds also. These animals and plants live propagate and die in the marine ecosystem. Sea water is the medium for their various physiological activities and their activities increase the salinity of the sea water.

All these facts show that sea and ocean water is salty and the percentage of salinity may vary from place to place.