Ours is the blue planet, and the hallmark of life on Earth is water. But where did this colorless, odorless liquid first come from?

"The question of the origin of water on Earth, or the question of why there is clearly more water on the Earth than on the other planets of the Solar System, has not been clarified. There are several acknowledged theories as to how the world's oceans were formed over the past 4.6 billion years." "Some of the most likely contributory factors to the origin of the Earth's oceans are as follows: - The cooling of the primordial Earth to the point where the outgassed volatile components were held in an atmosphere of sufficient pressure for the stabilization and retention of liquid water. - Comets, trans-Neptunian objects or water-rich meteorites (protoplanets) from the outer reaches of the main asteroid belt colliding with the Earth may have brought water to the world's oceans. Measurements of the ratio of the hydrogen isotopes deuterium and protium point to asteroids, since similar percentage impurities in carbon-rich chondrites were found to oceanic water, whereas previous measurement of the isotopes' concentrations in comets and trans-Neptunian objects correspond only slightly to water on the earth. - Biochemically through mineralization and photosynthesis (guttation, transpiration). - Gradual leakage of water stored in hydrous minerals of the Earth's rocks. - Photolysis: radiation can break down chemical bonds on the surface." "A sizeable quantity of water would have been in the material which formed the Earth." "Study of zircons has found that liquid water must have existed as long ago as 4.4 Ga, very soon after the formation of the Earth. This requires the presence of an atmosphere. The Cool Early Earth theory covers a range from about 4.4 Ga to 4.0 Ga. In fact, recent studies of zircons (in the fall of 2008) found in Australian Hadean rock hold minerals that point to the existence of plate tectonics as early as 4 billion years ago. If this holds true, the previous beliefs about the Hadean period are far from correct. That is, rather than a hot, molten surface and atmosphere full of carbon dioxide, the Earth's surface would be very much like it is today. The action of plate tectonics traps vast amounts of carbon dioxide, thereby eliminating the greenhouse effects and leading to a much cooler surface temperature and the formation of solid rock, and possibly even life." "The greatest proportion of today's water may have been synthesized biochemically through mineralization and photosynthesis (Calvin cycle)." Source and further information: http://en.wikipedia.org/wiki/Origin_of_water_on_Earth

God created it.