Fascinating stuff!
This and global warming is gonna get the water level up, maybe I should think about a boat dock...
Check out part four of his lecture:
http://smallcomets.physics.uiowa.edu/lecture/lect4.html
"The origins of our oceans always have been a fascinating mystery. In his classic paper of 1951 William Rubey... was puzzled by the large amount of water which was unaccounted for. Even at the time of writing his seminal paper he queried astronomers as to whether it was possible that this water was being supplied by an infall of objects from interplanetary space. The responses of astronomers were negative... Large amounts of water are now believed to be lost as subduction of continental plates carries oceanic water under the surface... This water was thought to be recycled to the surface by outflow of gases from volcanic activity. This was a natural suggestion in consideration of the dramatic activity of volcanoes... In a recent classic paper of 1999 David Deming reports on the amount of water which is returned to the Earth's surface by volcanic activity and finds that: 'The losses of surface water due to subduction into the mantle are greater by factors of 7 to 20 than the supply given by volcanic activity. The rate of a cosmic influx of water to compensate for the water loss to the mantle is similar to that derived by Frank and Sigwarth [1993] from observations of small comets.' ...The significance of the small comets is obvious: our Earth would be dry and barren without an extraterrestrial influx of water."