Biology Reference
In-Depth Information
8
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The Great Ice Ages
The relatively brief interval of the Quaternary, some 2.6 million
years duration, belies the great interest in and the importance of
this last geologic period (Pasini and Colalongo 1997; Balco et al.
2005; Gibbard 2007; Kerr 2008; Meltzer 2008). Its signifi cance
for us derives in no small part from the fact that it encompasses
the span of
Homo sapiens
. Assuming the species appeared about
160,000 years ago, all the world's ecosystems had long been estab-
lished, and the locales of human origin and the early routes along
which they dispersed had been alternating between near-desert/
savanna/grassland and more mesic forest.
Another intriguing aspect of the Quaternary was the disappear-
ance or major reduction in the great Pleistocene megafauna in
many parts of the world. This event took place globally between
about 50,000 and 10,000 years ago, it began in North America
with the crossing of Beringia by hunters at around 17,000 BP, and
it is documented by the fi nds at Murray Springs, Arizona, dating
from 13,500 BP (chap. 2). The possibility of Pleistocene overkill
