ABSTRACT

The presence of water on Earth has played important roles in shaping the solid regions of the planet as well as in the origin and evolution of life. This paper addresses three fundamental aspects of Earth’s water; (1) the quantity of water on the surface and in the interior that Earth possesses, (2) the length of time that surface oceans have been present, and (3) the mechanism(s) by which this water was supplied or generated. From geochemical and geophysical analysis, and high-pressure experimental works, the water content in the Earth’s mantle can be estimated to be from one to ten times the present ocean mass. Although it is difficult to estimate the water content in the Earth’s core, recent high-pressure experimental work indicates copious amounts of hydrogen in the core. From geological and geochemical evidence, the Earth’s surface oceans appear to have existed since very early in the Earth’s history, perhaps even since the Earth’s formation. However, changes in the ocean volume throughout the Earth’s history have not been well determined. Several possible water sources and supply mechanisms have been proposed, in association with theories regarding planet formation in our solar system. Since there are several uncertainties concerning the process of planet formation, the origin of the Earth’s water is still in question.