Links about threats:

Links More Links
War of the Worlds Apollo Quarantine
Carl Sagan  
Impacts on Earth Armpitageddon

Link to a movie about the history of the Moon

Apollo 17 surface panorama:

Apollo 17 panorama

One does not generally see this type of densely-cratered surface on Earth.  An exception is certain battlegrounds.  Here is a Google satellite image of the Pointe du Hoc site on the Normandy coast:

Pointe du Hoc
        Google

Ground-level images:

Pointe du Hoc promontory

Pointe du Hoc
        inland