Why is sea water so salty

When rain falls, it weathers rocks, releasing mineral salts that separate into ions. These ions are carried with runoff water and ultimately reach the ocean.

Around 3. Some mineral ions are used by marine animals and plants, removing them from the water. When water evaporates, the dissolved salts are left behind. So a few lakes are salty because rivers carried salts to the lakes, the water in the lakes evaporated and the salts were left behind. After years and years of river inflow and evaporation, the salt content of the lake water built up to the present levels.

The same process made the seas salty. Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to fall again as rain and to feed the rivers, but the salts remain in the ocean. Because of the huge volume of the oceans, hundreds of millions of years of river input were required for the salt content to build to its present level.

Rivers are not the only source of dissolved salts. About twenty years ago, features on the crest of oceanic ridges were discovered that modified our view on how the sea became salty. The sea often appears blue because of the way light interacts with the water. White light is made up of many different visible colours ranging from red to violet — red has the longest wavelength, blue light the shortest.

As water molecules are better at absorbing light with longer wavelengths, they absorb much of the red, orange, yellow and green light. The bluer colours, with shorter wavelengths, are less likely to be absorbed, giving the sea its blue hues.

Shallow water often appears clear as there are fewer water molecules to absorb the light, so other colours are able to reach the sea floor and reflect. The deeper you go, the more other colours are absorbed and the deeper blue the light becomes, until you reach the point where no visible light can reach, where it is completely dark.

The colour of the water also depends on other factors, such as what particles are floating in it. These vents contribute dissolved minerals to the oceans, which is one reason the oceans are salty. Credit: NOAA. Rivers and surface runoff are not the only source of dissolved salts. Hydrothermal vents are recently-discovered features on the crest of oceanic ridges that contribute dissolved minerals to the oceans. These vents are the exit point on the ocean floor from which sea water that has seeped into the rocks of the oceanic crust has become hotter, has dissolved some of the minerals from the crust, and then flows back into the ocean.

With the hot water comes large amounts of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of the oceans could seep through the oceanic crust in about 10 million years. Thus, this process has a very important effect on salinity.

The reactions between seawater and oceanic basalt, the rock of ocean crust, are not one-way, however; some of the dissolved salts react with the rock and are removed from seawater. A final process that provides salts to the oceans is submarine volcanism, the eruption of volcanoes under water.

This is similar to the previous process in that seawater is reacting with hot rock and dissolving some of the mineral constituents. Humans cannot drink saline water, but, saline water can be made into freshwater, for which there are many uses. The process is called "desalination", and it is being used more and more around the world to provide people with needed freshwater. In your everyday life you are not involved much with saline water. You are concerned with freshwater to serve your life's every need.

But, most of Earth's water, and almost all of the water that people can access, is saline, or salty water. Do you wear contact lenses? If so, you most likely use a saline water solution to clean them.