Geoscience Reference
In-Depth Information
the question of causes has aroused vigorous and all too often polarised debate (Martin
and Wright,
1967
; Martin and Klein,
1984
).
5.6.2 South America
The Spaniards had crossed the Andes and had successfully established small coastal
settlements in the drier parts of Peru and northern Chile from the sixteenth until the
eighteenth centuries on the edge of the driest desert on earth, the Atacama, but it was
not until the arrival of HMS Beagle in Patagonia in 1832 that scientific enquiry really
began. Here, as in so much else, it was Charles Darwin who led the way and posed
the relevant questions. Alexander von Humboldt (1769-1859) had earlier climbed
the Andes and kept detailed meteorological and natural history observations and was
held in great esteem by Darwin, who considered him 'the greatest scientific traveller
who ever lived', but Humboldt had little involvement with desert research in South
America. Darwin spent considerable time during 1832 and 1835 exploring the drier
regions of South America (Darwin,
1860
). He was intrigued by the discovery of half
a fossil skeleton of one of the large extinct mammals in Patagonia; dismissing human
predation as a causal factor, he concluded that gradual and almost imperceptible
changes in the environment were responsible (op. cit., pp. 171-175). He also found
geomorphic evidence that parts of Patagonia and the Cordillera had undergone tectonic
uplift (op. cit., pp. 169-171, 314-315). In the Cordillera, he observed abandoned
Indian settlements high in the mountains in regions now too arid to support life and
speculated that a slight increase in the occasional rains would have allowed irrigation
and human life (op. cit., p. 356). In another instance, he concluded that a river in
the Peruvian mountains had been diverted as a result of earth movements (op. cit.,
p. 358). On one occasion in Patagonia, he observed a local soldier striking fire with
the flint from a broken arrowhead. Darwin then searched for other arrowheads and
concluded that the flint arrowheads in this region were of some antiquity and predated
the reintroduction of the horse into South America (op. cit., p. 105).
All of the questions raised by Darwin after his travels in semi-arid South America
have been the subject of scientific enquiry ever since. The geographer Isaiah Bowman
(1878-1950) led a scientific expedition from Yale University through the Atacama,
culminating in his highly readable
Desert Trails of Atacama
(Bowman,
1924
). The
Atacama is a narrow coastal desert more than 1,000 km long with an area of approx-
imately 100,000 km
2
. Antofagasta in northern Chile has a notional precipitation of
1 mm/year, a somewhat meaningless figure but one indicative of hyper-aridity.
A recurrent question in South America concerns the reaction of the Amazon rain-
forest to Pleistocene climatic fluctuations (Colinvaux et al.,
1996
; Haberle andMaslin,
1999
; Colinvaux et al.,
2000
; Colinvaux,
2001
;Bushetal.,
2009
). Both the pollen
evidence (Anhuf et al.,
2006
) and the presence offshore of glacial age arkose (Damuth
and Fairbridge,
1970
) appear to favour glacial aridity, but not all workers are agreed,
