The Japan Times
June 6, 2001

Scholars devise method to gauge stone tools' age

OSAKA - A group of scholars in western Japan said Tuesday they have devised a method to assess the age of unearthed stone tools by examining the degree of weathering on their surface.

The group, led by Tsuneto Nagatomo, a professor at Nara University of Education, has found that the approximate age of stone tools could be calculated by measuring the thickness of crumbling layers on the stone's surface.

Nagatomo said he hopes the method will help verify the authenticity of controversial Paleolithic stone tools discovered in northeastern Japan.

Japan's archaeological world was thrown into chaos last year when archaeologist Shinichi Fujimura admitted planting artifacts allegedly dating back to the Paleolithic at two sites in northeastern Japan.

The new method is groundbreaking, according to the scholars, as there was previously no way to assess the age of tools other than those made of obsidian, which weathers at a constant rate and whose level of decay can be measured by detecting the degree of water it contains.

Nagatomo and other experts developed the new method by analyzing with microscopes the crumbling layers of stone tools from various periods discovered in western and northeastern Japan. They found that the shale layers of tools from the same region thicken in proportion to time.

While the method cannot be used to determine the exact age of ordinary stone tools, which do not weather at a regular rate, further examination of samples could determine whether certain items date back to certain periods of time, such as the Upper Paleolithic.

Previously, tests were only able to date the formation of rocks — not the period in which they were used to create a stone tool.

Archaeologists calculated the ages of tools by analyzing elements in volcanic ash buried in the same layers where the items were unearthed.

This calculation method proved vulnerable to falsification, however, with Fujimura allegedly burying at excavation sites ancient stone tools similar in appearance to those of the Paleolithic, only to later unearth them as supposedly new finds.