The Holocene Impact Working Group (HIWG)(a) was created by researchers into different aspects of geosciences, who believe that cometary impacts were more frequent during the recent past than generally accepted. It is concerned with the growing number of impact craters being discovered and the evidence of consequent mega tsunamis.
Its membership includes Mike Baillie, Richard Firestone and Bruce Masse(b).

(a) http://planetarydefense.blogspot.com/2009/02/holocene-impact-working-group-hiwg.html

(b) http://archaeology.about.com/od/climatechange/a/masse_king.htm