Subject: Moon crater survey and impact dating

I read recently that there was a probable 26 million year periodicity in meteor 
impacts on earth and that this possibly corresponded to extinctions. Jave 
crates on the moon been dated? In that case, has a periodicity there been 
observed? Craters on the moon may be less disturbed by plate techtonics, 
weather and life forms.
Also, does the moon have a magnetic field and if it does, has there been any 
detection of this magnetic field's variation such as it has on earth, and was 
there any relationship between the variations on both planets?

Re: Moon crater survey and impact dating