Re: geologic periods

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>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 was, as you note, referring to t he formal term "Period".

The base of the Cambrian has recently been reevaluated at 540 Ma, not 570,
based on new radiometric evidence.  Someone is on the libraries reference
computer at the moment, so I can't check for the title and authors, but
I'll post them later.

That loss of 30 million years tips the scales in favor of the Cretaceous.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.