Geological events of biological importance in the history of the Andes include their impact on global climates through an influence on atmospheric circulation, rainfall patterns, and the atmospheric concentration of CO2; habitat diversification from lowlands through páramo to glaciated peaks; and migratory pathways ranging from discontinuous (mesic elements), highly discontinuous (páramo elements), barriers (to east-west migrations), to selective pathways (via the dry Andean valleys). The timing of these effects is a function of the uplift history of three (to nine) morphotectonic segments of the Andes resulting in (1) mostly lowland swamp and fluvial environments in the Cretaceous and Paleocene, (2) moderate uplands beginning in the Late Eocene (ca. 40 million years ago [Ma]), (3) appression of an offshore volcanic chain (the proto–Cordillera Occidental) in the Oligocene (ca. 30 Ma), (4) uplift of the proto–Cordillera Oriental and the Altiplano to about half their present altitude by the Middle Miocene (ca. 15 Ma), and (5) uplift of the remaining half within approximately the past 10 million years. The early appearance of a biological community recognizable as the Atacama Desert is estimated at ca. 15 Ma, and the beginnings of a páramo at ca. 3.5 Ma. Longer-term (Milankovitch) and shorter-term (Younger Dryas, Medieval warm/dry period, Little Ice Age, Heinrich, and Dansgaard-Oeschger [D-O]) climatic events, known initially from the high latitudes, are now widely recognized throughout Latin America, including the Andes. They document a dynamic physical environment from the Cretaceous through the Holocene and on all timescales.
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Vol. 96 • No. 3