For us, oceans are perpetual and have existed for ever, but this is an illusion. At the very beginning of our planet Earth, our globe contained a lesser amount of mass. Dust and debris from the surrounding space in the form of millions of meteorites were attracted thanks to the gravity of the growing Earth and resulted in sufficient gravity to hold the original atmosphere of Hydrogen and Helium against the forces of the solar wind. Both chemical elements are abundant in space and were captured through the Earth’s gravity.
There were no oceans or seas to be found at that time. It was only molten rock with floating crusts on top. Due to the immense friction inside the Earth, rock melted, reacted with other elements and formed new rock types and water. This water rose to the surface in the form of superheated vapour and formed a new atmosphere with 71% water, 23% Nitrogen and 5% Sulphur components. Very slowly – in millions of years – this super hot vapour blanket cooled off and droplets started to condense onto dust particles. Only when the Earth cooled down further, the first ponds of boiling water were formed. This was about 3.9 million years ago. The young Earth didn’t have real valleys at that time and when it rained extremely heavy the water level rose equally everywhere, forming the first worldwide ocean. It was a truly blue planet with a sea where only the highest volcanoes arose like fire ejecting islands. This ancient sea cooled off further for another 100 million years till the first bacteria appeared, some 3,8 million years ago and till the photosynthesis (generation of energy with sunlight) appeared some 3.5 million years ago. With this process organic molecules are being created with water, Carbondioxide, and sun light as major components and with the generation of Oxygen. This Oxygen, in fact a by-product of the life at that time, will dramatically change the appearance of Earth and its oceans. At the time of the first ocean the crust – only a couple of miles thin – was mainly formed from basalt that repeatedly was melted again when it immersed into the molten rock below, due to the immense geological activity. When it cooled down slowly, granite was formed eventually and because it’s specific weight is lower than that of basalt, it surfaced. Over a long time these immense granite blocks formed the continents. Due to the continuous melting, breaking, separation and drifting of the crust the actual image of the Earth is formed, together with its oceans. Compared to the other oceans, the Atlantic one is a baby. It has been created by the breaking and subsequent drifting of Africa/Europe and North/South America, some 150 million years ago, at the time of the saurian. Since then it has developed itself in to the 2nd biggest ocean and still grows with a couple of centimetres (!!!) per year. Two factors – volcanoes/tectonic activity and life – will condition the fate of the oceans.