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New Geological Time Scale for 2012
From: Ben Creisler
This item has not been mentioned on the DML that I can recall, but a
new version of the geological time scale is out.
A pdf of the GSA 2012 time scale can be downloaded at:
A pdf of the slightly different 2012 time scale from the Geologic Time
Scale Foundation is free at:
Some dates such as those for the Pleistocene are given differently.
Note that the Mesozoic ended 66 million years ago on both scales,
although many sources still cite 65 or 65.5 million years ago as the
extinction date of the dinosaurs. The Cretaceous/Paleocene boundary
was dated to 65.95 million years ago back in 2008 as I recall.
For an article on the GSA version, see:
J.D. Walker, J.W. Geissman, S.A. Bowring and L.E. Babcock (2012)
The Geological Society of America Geologic Time Scale.
Geological Society of America Bulletin (advance publication)
The Geological Society of America has sponsored versions of the
geologic time scale since 1983. Over the past 30 years, the Geological
Society of America Geologic Time Scale has undergone substantial
modifications, commensurate with major advances in our understanding
of chronostratigraphy, geochronology, astrochronology,
chemostratigraphy, and the geomagnetic polarity time scale. Today,
many parts of the time scale can be calibrated with precisions
approaching less than 0.05%. Some notable time intervals for which
collaborative, multifaceted efforts have led to dramatic improvements
in our understanding of the character and temporal resolution of key
evolutionary events include the Triassic-Jurassic, Permian-Triassic,
and Neoproterozoic-Phanerozoic boundaries (or transitions). In
developing the current Geological Society of America Time Scale, we
have strived to maintain a consistency with efforts by the
International Commission on Stratigraphy to develop an international
geologic time scale.
Although current geologic time scales are vastly improved over the
first geologic time scale, published by Arthur Holmes in 1913, we note
that Holmes, using eight numerical ages to calibrate the Phanerozoic
time scale, estimated the beginning of the Cambrian Period to within a
few percent of the currently accepted value. Over the past 100 years,
the confluence of process-based geological thought with observed and
approximated geologic rates has led to coherent and quantitatively
robust estimates of geologic time scales, reducing many uncertainties
to the 0.1% level.