The very thought of the beach is relaxing to the human mind. The cool breeze, the gushing waves, the warm and salty peanut cones, and the golden globe that slowly plunges itself into the gleaming water leaving a yellow tint to the evening and painting the sky in myriad hues. But almost every one of us has had a salty brush with the sea as well that taught us the first lesson about seawater, that it is salty.

So, why is the seawater salty?

The obvious reason is the presence of dissolved “salts” in it. But who put the salt there?

The salt in the seawater has two sources to blame for its coarseness-the runoff from the land and the cracks in the seafloor. The huge rocks on the land are susceptible to erosion due to exposure to acidic rainwater. Eroded rocks release ions, which are then carried away via streams and rivers whose ultimate destination is the sea. Some of these ions are eaten up or used by the organisms leaving the rest of it to lie around and amass. Over time, their concentration in the water steadily increases.

The cracks in the seafloor are another source of salt in the seawater. The ocean water seeps into the cracks and fissures in the seafloor and gets heated up by the magma in Earth’s core. The heated water releases oxygen, magnesium, and other sulfates, and in turn absorbs iron, zinc, and copper from the near lying rocks. Underwater volcanic eruptions are also another source of salt in water.

85% of ions in seawater are chloride and sodium, magnesium, and sulfate make another 10%. Many other ions are also found in smaller quantities. All these dissolved ions from a number of sources combine to make the seawater salty. Salinity varies with temperature, but it is safe to deduce that approximately 3.5% of seawater weight is attributed to the dissolved salts.

So the next time the beach waves touch the unseen little gashes on your skin and a pinching pain shoots up your body, you know whom to blame and from where it comes from.