<P> Study of zircons has found that liquid water must have existed as long ago as 4.404 ± 0.008 Ga, very soon after the formation of 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 . </P> <P> 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, Earth's surface would be very much like it is today . The action of plate tectonics traps vast amounts of carbon dioxide, thereby eliminating greenhouse effects, and leading to a much cooler surface temperature, and the formation of solid rock, and possibly even life . </P> <P> Some terrestrial water may have had a biochemical origin, during the Great Oxygenation Event, via redox reactions and photosynthesis . </P> <P> In the early 1930s, Cornelis van Niel discovered that sulfide - dependent chemoautotrophic bacteria (purple sulfur bacteria) fix carbon and synthesize water as a byproduct of a photosynthetic pathway using hydrogen sulfide and carbon dioxide: </P>

What is the presence of water on earth