If you go to the beach this year, look at the sea. At that moment you will be before one of the strangest panoramas that our Universe offers: large amounts of liquid water .
Seas and oceans emerged from the interior of our planet shortly after it formed, 4 billion years ago. The water, trapped inside the Earth, came out through the many volcanoes and geysers present on the surface. This degassing was so rapid that in just one hundred million years the water needed to form the oceans was released.
However, not all the water arose from within the Earth. Between a third and half of the water came in comets – big dirty snowballs – that fell on our planet when it was still young during the time known as the Great Bombardment : not only sea water has not changed anything in several billions of years, but some of it has an extraterrestrial origin.
But not everything ends here. When my parents took me to the sea for the first time, I immediately established two unquestionable facts: that it was a very large pool and that the water was salty. Something fascinating, because the water of the rivers, from which the sea is nourished, is not.
Of course, river water is not just water. As anyone can see by reading the label on a bottle of mineral water, in addition to water there are different types of mineral salts. The problem is that river water has more dissolved calcium, potassium and magnesium than chlorine and sodium , the components of common salt, so there should be more of the former in the sea.
Because is not like that? It all has to do with time. Calcium remains in the sea for more or less a million years, because marine organisms use it to form skeletons and shells. Something similar happens to magnesium, and the potassium combines with the clays and goes to the bottom. But the times of chlorine and sodium are longer : sodium lasts about 60 million years and chlorine even longer. That is why the water is salty.
