Salt is soluble in water and so it passes into the seas and oceans with rain water. The salt present on the Earth’s surface is continuously being dissolved and passed into the ocean thus, making it salty.
If ocean could dry up, the salt could build a 180 miles high and 1 mile thick wall, covering once around the equator. The concentration of salt in sea water varies from 3% to 3.5%.
The Dead Sea with an area of 340 sq. miles contains about 11,600,000,000 tons of salt. The common salt which we all use is produced either from sea water, salt lakes and springs or from deposits of rock salt.
Below Seawater info from Wikipedia (Read More):-
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every 1 kilogram (2.2 lb) of seawater has approximately 35 grams (1.2 oz) of dissolved salts (mostly, but not entirely, the ions of sodium chloride: Na+, Cl−. The average density of seawater at the ocean surface is 1.025 g/ml; seawater is denser than freshwater (which reaches a maximum density of 1.000 g/ml at a temperature of 4 °C (39 °F) because of the salts’ added mass. The freezing point of sea water decreases with increasing salinity and is about −2 °C (28.4 °F) at 35 g/l.
http://en.wikipedia.org/wiki/Seawater
