Campus: Cal Poly, San Luis Obispo -- October 08, 2001
Cal Poly Professor Part of Team Conducting Research On Oldest Human Settlement in Northeast Asia
In collaboration with Chinese earth scientists, Cal Poly Physics Professor
Kenneth Hoffman has established the age of ancient stone tools found in
northern China: 1.36 million years. The tools now represent the earliest
known presence of humans in northeast Asia, according to an article published
in the September issue of the journal Nature.
The work is important because it places in time the earliest known human
settlement in Northeast Asia, providing an important piece of the puzzle
tracing the path and timing of human migration throughout the Paleolithic
Age, according to editors at Nature.
Hoffman was invited to Beijing in March 2001 by Dr. Rixiang Zhu of the
Chinese Academy of Sciences. Zhu's group at the Institute of Geology and
Geophysics had already conducted extensive research on the ancient dry-lakebed
sediments in which the stone tools were found.
However, the true age of the tools had remained a mystery since their
discovery in the remote Nihewan Basin at the Xiaochanglian archaeological
site in northern China more than two decades ago.
Establishing their age proved difficult because they were found in sediments
lacking the usual natural materials that typically give scientists reliable
materials for carbon- or other radioactive- isotope dating methods.
While in Beijing, Hoffman was able to review the Chinese data and help
establish the age of the stone tools using the "magnetostratigraphy"
of the sediment section.
This scientific technique involves the investigation of magnetic direction
of sediment layers.
"We know that Earth's magnetic field 'flips' polarity from time to
time in the geologic past, causing compass needles to switch direction
from pointing northward to pointing southward, or back again," Hoffman
explains. "And for the last several polarity reversals the ages are
rather precisely known."
Magnetic particles in each sediment layer record the direction of the
field at the time they are deposited and hold that direction through the
In Beijing, Hoffman was able to determine the sequence of magnetic polarity
recorded in the ancient sediment section from well above to well below
the layer in which the stone tools were found. Hoffman was then able to
establish the tools' age: 1.36 million years.
The date makes Xiaochangliang the site of the oldest known human settlement,
as well as the oldest assembly of recognizably Paleolithic stone tools
found to date in Northeast Asia.
Hoffman holds a Ph.D. in geophysics from the University of California
at Berkeley and is an internationally recognized expert in paleomagnetism
-- the study of Earth's past magnetic field -- and, in particular, polarity
reversal. The stone-tool paper is Hoffman's eighth publication in the
prestigious journal Nature since his arrival at Cal Poly in 1974.
Rick Potts, director of the Human Origins Program at the Smithsonian's
National Museum of Natural History and co-author of the paper, helped
provide the context and paleoarcheological significance of the result.
For more information on the Nature article or to purchase a copy, visit
the journal's Web site at www.nature.com.