With National Science Foundation support Dr. Hector Neff and his collaborators will complete the analysis of five sediment cores from Pacific coastal Guatemala that are known to span the time periods when people first began modifying the landscape for agriculture and other subsistence purposes. Preliminary results from one location suggest that people brought maize or a direct ancestor of maize to the region before 5000 B.C. and that dramatic agricultural intensification took place beginning around 3500 B.C.
The signal of human modification and other landscape changes can be detected in sediment cores via the changing frequencies of plant microfossils (phytoliths and pollen) and charcoal together with variation in sedimentation rates. When people cut or burn down the tropical forest for agriculture, weeds and charcoal become more common in the record as trees and other forest species decline. Sedimentation rates also tend to increase as forest cover is removed. Maize and other agricultural crops can be identified both from pollen and phytoliths, the combined evidence providing the most secure identification (phytoliths are microscopic silica bodies that accumulate growing plants). These changes are placed in a chronological context by AMS radiocarbon dating of organic matter from selected levels in the cores.
The period between 3500 B.C. and 800 B.C. in Pacific coastal Guatemala is of particular interest because it was during this period that many of the distinctive characteristics of Mesoamerican complex societies coalesced. By the end of the period, people in most locations depended heavily on maize agriculture, large sites with monumental architecture and elaborate stone sculpture were being constructed, and social stratification had appeared. The fundamental shifts in subsistence, the increased tethering of people to specific locations, and the beginning of major investment in architectural infrastructure constituted the emergence of Mesoamerican civilization. Unfortunately this Pacific region has been relatively understudied and details of the sequence are poorly known compared, for example, to the Olmec heartland on the Gulf Coast of Mexico. The work of Dr. Neff and his colleagues will both establish an environmental context for this cultural progression and provide insight into the process itself.
