How were oceans formed?
Since no people were here on Earth when the ocean was formed, scientists try to come up with their own explanations for how the oceans came to be. After all, there are no oceans on Mercury, Venus, Mars or the moon, so why should the Earth have seas? According to one theory, comets that had a lot of ice crashed into the Earth. But many scientists don't buy this theory. Yet another theory says that it must have rained for millions of years. Again, some scientists have their doubts about that one.
But where does the salt in the ocean come from? Some scientists think that ancient volcanoes spewed out chlorine into the atmosphere, in addition to water vapor. Perhaps the chlorine joined together with the water molecules to form hydrochloric acid. This hydrochloric acid may have eaten at rocks, causing them to release sodium. When the sodium atoms and the chlorine atoms came together, sodium chloride (salt) was formed.