Geoscience Reference
In-Depth Information
DNA supported by 1,439 directly dated megafaunal sites and 6,291 radiocarbon
ages associated with the Upper Palaeolithic human presence in Eurasia, and they
found that each species responded differently to the effects of climate change. They
concluded that climate change alone explains the extinction of the Eurasian musk ox
and woolly rhinoceros but that a combination of climatic and human impacts seems
to be responsible for the demise of the wild horse and steppe bison.
Polyak et al. (
2012
) bring a novel approach to this problem by using the
13
Cand
234
U values in speleothem calcite from Fort Stanton Cave in southern New Mexico
as a proxy for effective precipitation, supplemented by ages obtained from rim pools
in the Big Room of Carlsbad Cavern (see also
Chapter 14
). They found that a very
severe drought followed a moist pluvial interval and afflicted the south-western United
States from just before 14.5 until 12.9 ka or soon thereafter, an interval of time that is
broadly synchronous with the 14.6-12.8 ka Bølling/Allerød warming event evident
in the Greenland ice core record. They noted that the last appearance of sixteen out of
thirty-five mammal genera that became extinct between 13.8 and 11.4 ka overlapped
with this 1,500 year drought in the arid south-west and predated both the arrival of the
Clovis hunters and the highly controverted cometary impact invoked (most aptly) by
Firestone et al. (
2007
) as possible causes of the extinction of North American large
mammals. They dismissed evidence of a sparse pre-Clovis human presence in North
America (Waters and Stafford,
2007
) as unlikely to have a significant impact, although
they did not rule out some human contribution to Pleistocene extinction. Once again,
the question of causes remains open. Two difficulties noted by Martin (
1984
)inhis
global overview of the 'prehistoric overkill' model remain as valid today as they were
thirty years ago: 'There is no guarantee that the time of extinction will inevitably be
found by archaeologists' (op. cit., p. 392), and 'a conceptual difficulty has centered on
the failure of the fossil record of many regions to disclose ample evidence of extinct
faunas in kill sites in any other cultural context' (op. cit., p. 396).
17.6 Use of prehistoric stone tools as stratigraphic markers
Prehistoric archaeology can contribute to our knowledge of climatic change in deserts
in one additional albeit indirect way, namely, by providing information akin to that
given by more orthodox forms of biostratigraphic markers, such as plant and animal
fossil assemblages (see Chapters
3
and
16
). For example, in localities such as Olduvai
Gorge in semi-arid Tanzania, which has a long and reasonably continuous record of
prehistoric human occupation, the progressive changes in stone tool assemblages over
time have been grouped into Early Stone Age (ESA - Oldowan, followed by the Ach-
eulian), Middle Stone Age (MSA), Late Stone Age (LSA) and Neolithic. Potassium-
argon dating of volcanic ash or welded tuff units located above and beneath the stone
tool-bearing horizons has allowed the older African stone tool-making traditions to
be reasonably well dated. In the case of the younger assemblages, radiocarbon dating
