Yeah, there’s a topic around here about that I think... [sound of some drawers opening and closing), ah here we go:
Small Comets and Our Origins
University of Iowa | circa 1999 | Louis A. Frank
Posted on 10/19/2004 11:13:25 PM PDT by SunkenCiv
http://www.freerepublic.com/focus/bloggers/1250694/posts
There is nothing greatly objectionable about the presence of small comets or to the above impact scenario. The objections are directed toward the numbers, the numbers of such objects required to explain the yearly rates of atmospheric holes. A yearly rate of 1 to 10 events in our atmosphere would be generally accepted by the scientific community, 10 to 100 events might be forgiven, but a thousand such impacts raise considerable outcries on the basis of "current wisdom". The proposed rate of 10 million small comets impacting our atmosphere each year was generally greeted with scorn and ridicule. Remarkably, at this rate over the age of Earth, the small comets can provide enough water to fill our oceans.
Interesting stuff.