Re: Re: Geological periods

[Thomas_R_HOLTZ@umail.umd.edu (th81)]

>   For further reference, on my web page is the DML Geologic Ages lists.  I
>took these from a recent (1994) book dedicated to the science of Geology,
>and is, as far as I can tell, an excellent and accurate resource.  Bear in
>mind, however, that just as there is in paleontology, there can be a
>difference of opinion in geology.  The geologic time periods are
>distinguished by criteria than is somewhat subjective (such as when major
>extinction events occurred).

These events (geologically short in duration) are much superior to numerical
figures.  You can go to a cliff of sedimentary rock and point to an
extinction boundary.  You cannot point to a numerical date: you'd need
really long arms to encompass the whole range of uncertainty for those
abosolute values.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084