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Cenozoic evolution of deserts
A story that begins with tectonic uplift in the tropics and sub-tropics
thus ends with glaciation of the polar regions.
William F. Ruddiman
Tectonic Uplift and Climate Change (1997, p. ix)
3.1 Introduction
The Cenozoic era spans the last 65.5 million years (65.5 Ma) of geological time
( Tabl e 3 . 1 ) and follows the Mesozoic era that saw the proliferation and eventual
extinction of the dinosaurs. It is in the Cenozoic that the mammals flourished and,
in the last 7 million years, the African late Miocene and Pliocene hominids appeared
that ultimately evolved into our Pleistocene human ancestors ( Chapter 17 ).
The Quaternary Period, now internationally defined as beginning 2.58 million
years ago (Gibbard et al., 2010 ), comprises the Pleistocene Series/Epoch (2.58 Ma to
11.7 ka) and the Holocene Series/Epoch (11.7 ka to present) ( Tabl e 3 . 2 ). Plans are
afoot to subdivide the Pleistocene into four Stages or Ages, namely the Gelasian
(2.60 Ma to 1.80 Ma), the Calabrian (1.80 Ma to 780 ka), and, more tentatively, the
Ionian (780 ka to 125 ka) and the Tarentian (125 ka to 11.7 ka). The Holocene 'remains
as a series/epoch distinct from the Pleistocene, in recognition of the fundamental
impact of humans on an otherwise unremarkable interglacial' (Gibbard et al., 2010 ,
p. 101). However, a recent discussion paper suggests that the Holocene be formally
subdivided into Early, Middle and Late, with the respective boundaries between Early
andMiddle at 8.2 ka and betweenMiddle and Late at 4.2 ka (Walker et al., 2012 ). There
are proposals mooted to call the most recent slice of geological time the Anthropocene ,
in deference to our growing impact on the earth, but because human impact across the
planet is highly time-transgressive, reaching agreement on when this proposed epoch
might have begun will be far from easy, even assuming that the term serves a useful
purpose.
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