Why is there more sea than land on the earth's surface?

Sea and land - the answer to this question lies in the composition of the rocks which make up the outer portion of the earth's crust. Over large areas of the earth's surface these rocks are lightish in colour relatively light in weight and are called granitic rocks because granite is the most common type. Over still larger areas of the earth the rocks are darker heavier and are called basaltic rocks since among them basalt is the chief type. We known that the earth at a depth of a few hundred miles below the surface is molten and that the surface or crustal rocks which are about 50 miles thick are really floating on this liquid core. The granitic rocks stand higher than the basaltic just as a cork floats higher than wood and therefore the granitic areas are the continents and the basaltic the ocean basins. If all crustal rocks were of the same composition the earth's surface would be one vast ocean, more than a mile deep. But why is there water in the sea? There are three reasons. First, molten rock holds much more water than when it hardens and cools. So, as the earth's crust solidified it gave off water vapour into the atmosphere. Secondly, the earth's gravity stops this vapour from escaping into space just as it also retains the atmosphere we breathe. Thirdly, the pressure temperature relationships on earth are such that the vapour is mainly in liquid form. The water in the sea is salty because of the 2,000 million years old disintegration of the earth's crust. The soluble materials or salts remained in the ocean. The insoluble materials have formed sedimentary rocks and the ocean sediments.