why is there more sea than land on the earth’s surface
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 color, 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.
The more granite there is, the more continent there is, and the more of the Earth’s surface rises above the ocean basins. Water fills the basins. Right now, there is more basin than continent, and so more ocean surface than land surface.
We know 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.
The surface of the Earth is covered about 70% by water and it may seem like most of Earth is composed of water, but actually it’s a much smaller amount of water compared to the rocky planet – about 0.5% of the whole entire planet is water.
But why is there water in the sea? There are three reasons. First, the elements hydrogen and oxygen were present in the mass of material from which the earth was formed. These later formed water in vapour and liquid forms. Secondly, the earth’s gravity stops the 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 water is mainly in liquid form.
The water in the sea is salty because of the 2,000 million-year 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.