[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.

[SunkenCiv]

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The Big Splash: A Scientific Discovery That Revolutionizes the Way We View the Origin of Life, the Water We Drink, the Death of the Dinosaurs, the Creation of the Oceans, the Nature of the Cosmos, and the Very Future of the Earth Itself by Louis A. Frank and Patrick Huyghe

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[wideminded]

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.

IIRC he had a telescope that scanned the sky in UV. He noticed black dots that appeared against the background and then disappeared. He interpreted these as large "snowballs" that were continuously entering the upper atmosphere and melting. (Water absorbs UV). The problem was that the dots he was seeing were never larger than 1 pixel. Critics claimed he was just seeing noise from his detector. Frank planned to build a build a better system, but I never heard what happened after this.