Expert: Courtney Seligman - 2/28/2009

Question
Courtney:  I have studied cosmology for about 30 years, and a question keeps popping up in my mind. Where did all the water here on Earth come from?  There is somewhere in the neighborhood about 326 million trillion gallons of water on/in or just above the earth's surface.  In order to make this amount of water, it must have required an immense amount of hydrogen gas, and a smaller amount of oxygen gas. I have a theory that this hydrogen gas encircled the earth some 4 billion years ago and when the earth's crust ruptured, it spewed out various gases, chiefly oxygen which mixed with the hydrogen gas and a chemical reaction took place which formed clouds and eventually fell back down as rain.  Is my theory wet or could this be the source of all that water?  Also, do you know of any astrophysics professors who I could write to as I am thinking of writing a paper about stellar evolution and planetary formation.   Thank you.

Answer
A small portion of the water may have come from cometary bombardment, particularly in the period around 4 billion years ago, when it is thought that cometary objects in the outer solar system were disturbed by gravitational interactions with the Jovian planets. However, most is believed to have been trapped inside the Earth during its formation, not necessarily as water, but as other compounds of hydrogen and oxygen, then released to the surface when the planet melted and differentiated, shortly after its formation. Even now, huge amounts of steam and other gases escape from the interior of the Earth, as a result of 'hot spots' carrying mantle material toward the surface. Multiply current 'outgassing' by the much greater amount of volcanic activity when the planet was more molten than not, and you could easily develop an atmosphere hundreds of times thicker than what we currently have, primarily composed of various compounds of carbon, nitrogen and oxygen with each other and hydrogen. The hydrogen compounds were mostly lost, save for water, as a result of photo-dissociation (breakdown by ultraviolet radiation), and carbon dioxide was mostly dissolved in the oceans, then precipitated out as various carbonate rocks (e.g., limestone).

For a much more detailed discussion of this topic, refer to The Formation and Evolution of Planetary Atmospheres on my website, at http://cseligman.com/text/ssevolve/atmosphereevol.htm

As far as whom you should contact about a scientific paper -- Any university website will list the names of the various professors and assistant professors of astronomy, and their research interests. Whether they'd be willing to read unsolicited manuscripts is another matter, but if you contact enough of them, you should be able to find someone.

Courtney Seligman