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RE: Age division?
> From: email@example.com [mailto:firstname.lastname@example.org]On Behalf Of
> Jordan Mallon
> I've heard things like "_T. rex_ was from the Late
> Maastrichtian," but does
> this really mean anything quantitatively? Are geological ages separated
> according to time like that? (i.e., would "Late Maastrichtian" mean
> something like 68-65 Ma?) I'm just looking to put some numbers to these
> distinctions. I get the impression that anything past the Age
> category is
> fairly subjective.
Well, Mesozoic Stage/Age units have informal substages, based on particular
magnetic chronozone or biochronozone units, sometimes these are informal.
However, "informal" doesn't equal "subjective": these can be pretty secure
as being in the earlier part or later part of the unit, even if
international stratigraphic committees don't officially recognize a
And PLEASE don't make the (admittedly very common) mistake of thinking that
the geochronological units are defined by numerical time (i.e., 65 Ma)!
Absolute time represents *measurements* of units defined on other data, and
as such are subject to error bars of various sizes.
Thomas R. Holtz, Jr.
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
College Park, MD 20742
Phone: 301-405-4084 Email: email@example.com
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796