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Re: The Mesozoic timeline
I've forwarded this reply to the whole dinonet, since I'm sure there are
others out there who are interested:
>> Cretaceous Late Cretaceous Maastrichtian 65.0
>> Early Cretaceous Albian 97.0
>> Jurassic Late Jurassic Tithonian 145.6
>> Middle Jurassic Callovian 157.1
>> Early Jurassic Toarcian 178.0
>> Triassic Late Triassic Rhaetian 208.0
>> Middle Triassic Ladinian 235.0
>> Early Triassic Spathian 241.1
>I have a question which has always confused me:
>SOmetimes the terms "Upper" and "Lower" are used instead of late or early.
>But I never get them right: is Upper/Lower the Late or the Early period?
Upper, Middle, and Lower refer to the rocks themselves: The youngest rocks
in a system or series are Upper, oldest are Lower, and sometimes there is a
Middle. So, the Hell Creek Formation is an Upper Cretaceous rock unit.
Late, Middle, and Early refer to the time in which the rocks were
deposited: the Lower rocks in a system or series were deposited first, so
they are Early; the Upper rocks were deposited last, so they are Late. So,
the dinosaurs whose fossils are found in the Hell Creek Formation lived
during the Late Cretaceous.
>I think it is Upper=Late and Lower=Early, so you look at time "accumulating"
>upward and not "coming down".
Thomas R. Holtz, Jr. email@example.com
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