THE CASE FOR A COSMIC HERITAGE

The kinds of effects listed below would all have been experienced, and experienced repeatedly. Throughout our history the probabilities of cometary impact would by no means have remained uniform, as we shall shortly see. Rather one would expect to find significant bunchings of collisions, for the simple reason that fragmentation events due to planetary encounters occur on a discrete basis.

Energy

Diameter
(for ice comet with v=13.5 km/s)

Effects
1 MT TNT
(50 Hiroshima bombs)
70m Disintegration at high altitude, h>30km
10 MT TNT
(500 Hiroshima bombs)
140m Explosion in low atmosphere or surface impact; localised blast
102 MT TNT
(50,000 Hiroshimas)
322m Localised blast damage; tsunamis
103 MT TNT
(50,000 Hiroshimas)
700m Extensive blast damage; fires, tsunamis
105 MT TNT
(50,000 Hiroshimas)
3.22km Extended cratering; global effects; climatic changes; crop failures, famines
106 MT TNT
(50,000 Hiroshimas)
7km Mass extinctions