Why is the sea salty? Some say, because of the sharks' tears:
Video (Haifisch by Rammstein, 2010)
Und der Haifisch der hat Tränen
Und die laufen vom Gesicht
Doch der Haifisch lebt im Wasser
So die Tränen sieht man nicht
In der Tiefe ist es einsam
Und so manche Zähre fließt
Und so kommt es dass das Wasser
In den Meeren salzig ist
However, despite the lyrical perception of Rammstein, the actual reason the sea is salty is because it is very old. Oceans on Earth have existed for a very long time; therefore lots of salts were added to the water at a time when gases and lava were spewing from increased volcanic activity. The carbon dioxide dissolved in water from the atmosphere forms weak carbonic acid which dissolves minerals. When these minerals dissolve, they form certain chemical compounds, such as sodium chloride, magnesium sulfate, potassium nitrate, and sodium bicarbonate, which make the water salty. While water evaporates from the ocean, the salt gets left behind. Also, rivers drain into the oceans, bringing in additional ions from rock that was eroded by rainwater and streams.
Most lakes tend not to be salty, because water often leaves lakes to continue its trip toward the sea. A drop of water may remain in a lake for at most several decades, while a drop of water may remain in the ocean for 100-200 million years!
