Finally, pretentions of knowledge substantial enough to shoot down
It doesn't take an especially large impact to cause global catastrophic consequences - for that matter it does not take an impact at all -
All that is required is sufficiently heavy atmospheric dust loading - whether by impact or air burst does not matter
Even given the ages of the land areas Hoffman cites, they are of small area as a part of the globe -
The record of recent impact events, such as has been developed, is as I gave it...
EP