Abstract

The Atacama is a vast, rocky, hyperarid desert nestled between the Andes to the east and the Pacific Ocean to the west. Despite an extended history of hyperaridity (since the Mio-Pliocene), global climate fluctuations during the late Quaternary have been well-documented in the Atacama, both within and on the margins of the hyperarid core (where annual rainfall <10 mm). Major pluvial events occurred during the late Pleistocene (aka the Central Andean Pluvial Event, CAPE 17.5-10 ka) as well as during the Holocene (7.6-6.6 ka and 1.5-0.8 ka). These had major impacts on the distribution of the flora, fauna and consequences even for the peopling of this region of the world. During the CAPE, increased rainfall (up to five times greater than today) provoked downslope migrations and invasions into the hyperarid core, increased fluvial discharge, and elevated groundwater tables which in turn created riparian corridors and wetlands that facilitated dispersal across regions of the hyperarid core. Conversely, as pluvial events abruptly ended, wetter species became spatially restricted, in some cases to highly endemic regions on the Altiplano or to local oases/perennial rivers. These “pluvial relicts” can be found where plants have managed to subsist under favorable microclimates. Paleoecological evidence reveals that some species, however, did not survive the Holocene and are now locally extinct. Given the abundance of paleowetlands, we tested for evidence of an extraterrestrial impact proposed to have occurred at the end of the Pleistocene (12.9 ka) but the abundance of markers found requires an alternative explanation.