Olive oil has been a highly sought-after commodity for millennia, with evidence of cultivation since Neolithic times.
Only researchers at Cornell University are now saying its presence in ancient artifacts may be overstated. This is because the degradation process could cause other plant oils to be mistaken for olive oil. The team, writing in the Journal of Archaeological Science, is now calling for a re-examination of the criteria typically used to identify residue in excavated pottery.
“There’s definitely a sense among archaeologists of wanting to believe that you found olive oil, because it makes a nice story. And because it’s such an economically important Mediterranean product, there is a default assumption that if you found molecules that match olive oil, then you must have found olive oil,” Rebecca Gerdes, the Hirsch Postdoctoral Associate at the Cornell Institute of Archaeology and Material Studies, said in a statement.
“The problem is that olive oil overlaps in its composition with a bunch of other plant oils. And if you start to degrade it, then it gets even worse — it starts looking like an animal fat,” Gerdes said.
Read More: The Discovery of 7,200-Year-Old Cheese and Other Ancient Food and Drink
The Problem With Alkaline Soil
Excavated pottery often contains chemical compounds (or biomarkers) that can be used to determine what the pot once carried. Plant oils, for instance, can be identified by the presence of certain saturated and unsaturated fatty acids, as well as the oxidation products of unsaturated fatty acids, such as diacids.
“I usually describe my work as: I wash ancient dirty dishes, I save the rinse liquid, and I use the molecules in it to figure out how people are using their pots,” said Gerdes.
The problem is that Mediterranean soil is not conducive to preserving chemical biomarkers. The region’s climate, combined with its alkaline soil rich in calcium carbonate, “catalyze” the degradation of residue that might be contained within ancient artefacts, the study’s authors wrote.
To find out just how damaging an environment it may be, the team investigated how the amount and composition of olive oil residue changes in calcareous, alkaline soil from Cyprus versus mildly acidic soil from New York.
Recreating Archaeological Conditions
First, the researchers made 3-centimeter ceramic pellets from terracotta clay. These were submerged in olive oil overnight before being buried in soil imported from Cyprus or soil collected from an agricultural field in Ithaca, New York. The samples were then stored at 77 or 122 degrees Fahrenheit (25 or 50 degrees Celsius) for 3, 8, or 12 months. Once the time had elapsed, the team removed the samples from the soil and extracted the residue, ready for analysis.
“We managed to do it in the lab at an accelerated rate, so we didn’t have to wait 3,000 years to finish my Ph.D.,” Gerdes said.
The results show that olive oil residues in Cypriot soil were less well preserved than those in New York soil, with lower yields and greater losses of dicarboxylic acid plant oil biomarkers. The effects were most pronounced in samples incubated at the higher temperature (122 degrees Fahrenheit or 50 degrees Celsius).
The researchers put forward several potential explanations, including the possibility that leaching occurs more rapidly in Cypriot soil and that the two soils trigger different oxidation processes.
Rewriting Olive Oil History
This may change what we know about Eastern Mediterranean history during periods of early globalization, such as the Late Bronze Age (1650 to 1100 B.C.E.), the study’s authors say.
In Cyprus, for example, it is thought that large-scale olive oil production played an essential role in the country’s agricultural economy during this period, helping to secure its role as an important player in the region — a theory known as the “olive oil hypothesis.” Only this theory relies on evidence that might not be as foolproof as once thought, banking on the presence of fatty acids that are “consistent but not unique” to olive oil.
“We therefore suggest caution when extracting and interpreting organic residues from calcareous, alkaline contexts: the full suite of biomarkers for plant oils may not be preserved,” the study’s authors wrote.
Read More: Bronze and Iron Age People Focused on Olive and Grape Crops, Making Wine and Olive Oil a Priority
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a new study that was published in the Journal of Archaeological Science. Overlooking environmental context causes misidentification of ancient Mediterranean plant oil in organic residues
