4SEAS

Much of the rain that falls on the land started as water vapour which evaporated from the surface of the seas and oceans into the atmosphere. as the air moves around the globe, the water can be transported over great distances and under the right conditions, the water vapour forms clouds and rain. Rain that falls on the land can run over, or though the ground into streams and rivers, eventually returning to the sea. this is called the water cycle, and it is also the main reason why the sea is salty.

When water evaporates from the sea, all the minerals which make seawater salty are left behind - this is why rainwater is freshwater. But even rainwater can contain minute traces of minerals dissolved out of the atmosphere, and as water falls on the land and washes into rivers, it dissolves more minerals from the rocks and soils it washes over. So, over millions of years, minerals are transported into the seas making it salty as they are concentrated by the evaporation of water vapour.

Other minerals enter seawater from submarine volcanoes and hydrothermal vents, but it is not very likely that the sea is getting saltier and saltier as other chemical processes remove salts and minerals from seawater and they fall to the seabed to become muds and other sediments. Over millions of years, these sediments may form new rocks or be reabsorbed into the earth's core.