ABSTRACT
Oceans and connected seas cover more than 70.8% of the Earth with salt water to an average depth of about 3700 m, a volume that contains 97.2% of all the water on or near the surface of the planet (Thurman and Trujillo 2002). Oceans are so extensive that evaporation of seawater greatly exceeds that of land. As a result of wind transporting rain clouds inland, continents receive much more water than they lose in evaporation, resulting in an abundance of freshwater (e.g., see Smith and Smith 2001). Also, the separation of continents on the globe produces a moderating effect on their climate because water has a higher heat capacity than land. The present distribution of continents also produces much continental shelf habitat, which greatly enhances global productivity.
