How was a sea created?

Answer 1

It was originally thought that water on earth must have come from comets and ice rich asteroids. It was thought that water must have come to earth after formation. Since we are so close to the sun the water would have evaporated away to space when the proto-earth was smaller.

There is evidence in the form of zircon crystals from 4.38 billion years ago that tells us that only 187 million years after formation. This was just not long enough for extraterrestrial objects to bring us the water. Therefore water must have been there from when earth formed.

One recent theory overcomes these problems by suggesting that the earth formed further out in the solar system and migrated in to it current orbit as it grew in mass. Since it was in a cooler orbit water could condense on the rocks and as the earth grew and as the surface cooled water literally oozed out of the rocks and into the atmosphere. When the earth cooled further it literally rained for millions of years. This water went to form the 1st oceans.

This is not the complete picture however. Studies of fossil water trapped underground for billions of years taken from volcano's in Hawaii and Iceland show that the ratio of isotopes of heavy water do not match the water we have in the oceans today.

The only credible answer to this is that about 1/2 the water on earth today was already on earth when it formed and the other 1/2 comes from comets and ice rich asteroids.

Answer 2

When the earth was formed most minerals underwent a slow chemical process through millions of years and the gases in the environment (hydrogen and oxygen) condensed as ice .After the increase in global temperature and melting of ice with the quick climatic changes most salts were dissolved in water to make it saline. When the climatic changes stabilized , the cycle of precipitations with the surface runoff , the concentration of salt became higher.