Seas are in contact with many rocks which contains Salts but rivers are not in contact with them so the seas are more saline than rivers.
1 3 1
The water in the clouds was acidic and fell to the earth in huge rain storms.The acid in the rain dissolved the rock. Sodium released from the rocks mixed with chloride in the acid to form sodium chloride, which is a kind of salt. The result was salty water, and it filled in the lowlands and formed the oceans.When the volcanoes stopped erupting, the rain became less acidic, and so the creation of salt slowed down.Fresh WaterWhen sea water is warmed and evaporates into the atmosphere, the salt that it contains is left behind. When this water precipitates over land in the form of rain or snow, it feeds freshwater bodies such as rivers and lakes.Scientists believe that 3.8 million years ago there were a lot of volcanic eruptions, which formed clouds of ash.