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at an elevation of 2550 m. It formed between 6 and 3 Ma with uplift of the
mountains, and has been subsiding since the end of the Pliocene. It is now
fi lled with an almost continuous sequence of sediments and plant micro-
fossils dating to 3.2 Ma. For more than fi fty years, this exceptional trove
of vegetation and environmental information has been studied by Thomas
van der Hammen, and now by Henry Hooghiemstra, A. M. Cleef, and oth-
ers at the University of Amsterdam and in Colombia (Hooghiemstra 1984;
Hooghiemstra et al. 1992; Hooghiemstra et al. 2006). Among the results is
the demonstration that páramo and Andean forest zones (fi g. 2.42) moved
up and down slope in concert with climatic and glacial cycles. Also, the
major changes followed a periodicity of about 100,000 years. In the glacial
intervals, temperatures are estimated to have been about 8°C colder at the
high elevations, and this extrapolates to cooler conditions in the lowlands
now documented at around 5°C-6°C. In fact, the early studies by van der
Hammen were among the fi rst to suggest that the idea of a stable and un-
changing lowland neotropical rain forest was a myth. Early human infl u-
ence on the vegetation is evident between 4810 and 3800 BP, and between
3800 and 2470 BP. There is crop cultivation ( Zea mays ) and abundant char-
coal in the sediments (Gómez et al. 2007).
Human occupation
To the south in Peru, new information on human occupation and coastal
sediments also reveal the antiquity and impact of El Niños on ancient civi-
lizations in the region, and a wealth of intriguing geological and biological
data are additionally preserved in rapidly melting ice caps. The earliest and
most certain evidence of humans in Peru is from the lowlands at 12,000-
11,000 BP. The record of agriculture can be traced back about 4000 years
from starch grains and phytoliths of Zea mays and Maranta arundinacea (ar-
rowroot) found on tools and in soils at a preceramic house at Waynuma,
southern Peru (Perry et al. 2007). This extends the evidence for cultivation
from previous studies back by more than 1000 years. As noted, accurate
information on the appearance of farming in an area, as opposed to sub-
sistence by hunting and gathering, is important because like catastrophes
(e.g., megafl oods, volcanism) it represents modifi cation of vegetation by
a factor other than climate. Agriculture was established in many places in
South America by 6000 BP, and after that time the interpretation of spore
and pollen diagrams must take into account possible disturbance from hu-
man activity.
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