Mass Spectrometry Unearths
Mexico's Maize
Maize is a staple
food crop of many prehistoric socieities
and many scientists believe that the food
originates from teosinite which is native
to the Balsas River Valley of the Pacific
Slopes in southern Mexico. Much of this
region receives annual rainfall of 1500mm
and annual mean temperatures of 25C and is
covered by a tropical deciduous
forest.
In 1966 a cave located in the valley of
the Mexico highlands region of Oaxaco
found several living floors believed to be
have been occupied by early human
inhabitants. Zone A, the uppermost level,
contained a diverse array of domesticated
plant life that was dated between 620-740
A.D. In addition to the long time
occupants, shorter visits known as
"ephermeral occupations" were thought to
have been made to the caves pre 620 A.D.
These visitors left behind four-small
primitive looking maize cobs which occupy
small areas of ash just below Zone A.
Accelerator mass spectrometry has been
used to determine the age of maize cobs in
Oaxaco. Radiocarbon dating placed the age
of the maize cobs at over 6200 years old,
or some 4200 years B.C., making them the
oldest known agricultural crops in the
Americas. This finding, in addition to the
unequivocal domesticated nature of the
crops, leaves open the question of when
agricultural practices to cultivate maize
and related crops began. These early
farmers were likely mobile hunters and
gatherers so that the handful of caves and
rock shelters in the valley so far
excavated do not necessarily represent
those in which the practice began.
The full article appears in the February
13 issue of the Proceedings of the
National Academy of Sciences USA.