Evrim Yazgin
Cosmos science journalist
Archaeologists have used new techniques to study the ancient equivalents of modern kitchen tools used by Native Americans thousands of years ago.
Today, we have the mortar, pestle and cutting board. Ancient peoples around the world used to use manos and metates.
A metate is a large, flat stone or depression ground into a rocky surface. A mano is hand-held stone tool used to grind and pulverise plant and animal materials in a metate. Open-air metates are those that are ground into bedrock. These are relatively common at archaeological sites. Some are more than 15,000 years old.
New research published in the journal American Antiquity uses new microscopic techniques to understand the use of mano and metates by ancient Native Americans.
The team focused on bedrock metates found in Warner Valley, Oregon in the western United States.
“People have lived here for time immemorial and have been processing native plants on ground stone tools for a long time too,” says first author Stefania Wilks, an archaeobotanist at the Natural History Museum of Utah (NHMU) and a graduate student at the University of Utah.
In Utah, metates are typically oblongs carved into the exposed bedrock which is mostly sandstone. In other parts of the world, metates can be circular and deep. Metates around the world typically appear in groups or in rows.
NHMU’s curator of archaeology and University of Utah professor of Anthropology Lisbeth Louderback suspected that bedrock metates might be an untapped source of starch granules left behind when ancient people processed plant matter.
Louderback thought that small crevices in the rock might have protected granules from being swept away by wind and rain for thousands of years. She was right.
The team used an electric toothbrush and water to scrub material from the surface of the metate. Then they added a deflocculant – a substance similar to laundry detergent – to break up clumped particles and release them from crevices within the stone.
They repeated the process on nearby rocks that weren’t used as metates to serve as a control.
Returning to the lab, the samples were placed under the microscope. They confirmed that they had released starch granules from the crevices of the bedrock metates. The next step was to work out which plants the ancient people were processing on them.
Granules left behind on the metates were no larger than a tenth of a millimetre across.
Wilks analysed hundreds of starch granules, comparing their shape and features to those of plant species growing in the area.
Among the plants were a group of plants called biscuit root – part of the carrot family. There was also evidence that wild grasses, probably wild rye, were processed. They also found plants from the lily family.
All of these plants were and continue to be important food sources for local indigenous people.
The new method for uncovering ancient starch samples opens up a new avenue for studying the diets of ancient people around the world.
“Starch analysis is helpful in studying human diets of the past because some plant parts don’t preserve in the archaeological record,” Wilks says.
