[Smokin' Joe]

I first read about it in "The Big Splash" By Dr. Louis Frank (in part).

[Gazoo]

Maybe Dr. Grafenberg knows.

[ngc6656]

A Google search turns up that Dr. Louis Frank proposed in the 1990s that Earth's atmosphere is continuously receiving water vapor as many small comets evaporate there. Other sites that turned up in the search allude to the decades old theory put forth by planetary scientists that Earth's oceans were the product of the impact of large comets.

Study of Comet Hale-Bopp revealed that most of its water is of the heavy type containing the heavier hydrogen isotope named deuterium. If Hale-Bopp was a typical large comet, why then doesn't our oceans contain greater amounts of heavy water, they point out. Investigations continue.