A long time ago – a very long time ago – obsidian was all the rage. Abundant in Oregon and relatively easy to craft, Native American cultures used the volcanic rock to make prehistoric tools: knives, spear tips and the like.
“They’re razor sharp, sharper than any steel could be ground,” said Dennis L. Jenkins, Ph.D., senior staff archaeologist at the University of Oregon, who presented Friday at Tamastslikt Cultural Institute.
In his lecture, entitled “Obsidian: History Through the Volcanic Glass Window,” Jenkins touched on the wealth of information contained in the rock artifacts found all over the state, and how archaeologists can trace the movement of those artifacts from their original source.
“There will be these rare minerals in there that can be chemically identified, and they are unique to each volcano,” Jenkins said.
By a special X-ray procedure archaeologists can match the mineral composition to a specific volcanic source in the Western United States.
“And that allows us to track each individual artifact back to the exact location where it came from,” he said. “And it’s not uncommon in a particular site to find up to 30 or 40 obsidian sources represented there.”
Furthermore, archaeologists can trace the movement of obsidian artifacts by a fairly simple process. Whereas ancient peoples who crafted the tools would begin with large, often fist-sized cores, they would break them down, leaving millions of tiny flake pieces at the source location.
But the tools themselves would get smaller and smaller through time as their owners traveled and sharpened them, leaving further trails of flakes. Thus, as a general rule, Jenkins said the smaller the artifact, the farther it is from the original source.
“They were leaving a trail of evidence behind them,” he said.
For figuring out the age of the artifacts, Jenkins described multiple dating techniques, including a process called obsidian hydration.
As obsidian naturally absorbs water from the atmosphere, archaeologists can measure the amount of absorption and determine the time it took to occur. They first, however, must calibrate that measurement to the average soil temperature of the location where it was found.
Alternately, through a method called seriation, archaeologists sometimes can guess the general date of an obsidian tool based on its appearance.
“Technology improved through time,” Jenkins said, showing slides of increasingly sophisticated tools.
While ancient hunters may have begun by crafting relatively oval-shaped tools around 13,500 years ago, by about 2,000 years ago they were able to make extremely swift-moving arrow points.
Jenkins concluded by demonstrating the results of a study he helped conduct, examining the source and age of about 5,600 obsidian artifacts in Oregon. What he found were a few general pattern areas in which obsidian artifacts traveled with their owners north and south, with little east to west movement from the source. Jenkins presented a few ideas for that pattern, saying valleys more or less corresponded with the boundaries.
“Maybe this is a product of just normal movement through the environment on a north-south access,” Jenkins said.
Also, as old storm patterns would have moved west to east, the ancient cultures may have migrated north and south, carrying their resources along the way.