Why do we have an ocean?

Abstract

The question at first seems rather straightforward - we've got lots of water, and 97% is in marine realm. Most oceanography texts tell us the Earth's surface is 71% - we are the blue planet. But little more attention is paid to why we have an ocean, as we know it. There is water ice on 19 moons of giant planets, with a distinct possibility that Jovian moon Europa may have a liquid ocean beneath an icy crust. Evidence from Mars suggests large volumes of liquid water (lakes, small oceans) may have been present in past, and large channels and gullies on Martian surface show evidence of liquid (water) erosion. Yet nothing in our solar system compares with Earth's marine dominance. To make an ocean like Earth's, several elements are required: (1) a large volume of liquid, (2) this requires elements forming liquid be plentiful, (3) compound must have a prominent broad liquid phase, (4) gravity to retain fluid, (5) depressions to contain fluid if land and ocean are to be separate, (6) an atmosphere, and (7) luck - proper narrow distance from a solar source. This paper assesses these requirements and demonstrates why Earth is unique in our solar system, and that life as we know it is dependent on these variables.