Geologic Periods

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Tony Fiorillo wrote:

>At the level of geologic period, the Cambrian was longer by several millions
>of years (approximately 90 vs approximately 75).  Obviously the Precambrian
>is a formal period of time and is the longest formal time increment.

I had the same reaction, but according to the Harland et al 1989 time
scale, the
Cambrian was only 60 m.y. (570 to 510) and some recent papers (?Geology 1994?)
suggest that it was even shorter.   Harland et al set the Cretaceous at 81 m.y.
(132 to 65).

 Regards.
  Brian
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