Burned grains hold clues to ancient farms
26 June 2009
A granary that burned down 2300 years ago stored wheat from a single, carefully farmed harvest, research suggests. The findings are based on chemical comparisons of old and modern wheat grains and give new insights to Bronze Age farming practices.
The granary at Assiros Toumba in Greece burnt to the ground around 1300 BC, during the Bronze Age, together with large quantities of grain stored in clay bins and jars. It was a large facility and the fire was 'undoubtedly a catastrophic accident for the people whose grain was stored there,' says Professor Glynis Jones, an archaeologist from the University of Sheffield.
The reasons for the fire are unknown - it could have been accidental or may have happened in the aftermath of an earthquake, Jones suggests. But there is no solid evidence to support either theory.
Archaeologists also did not know what kind of wheat was stored at Assiros Toumba: was it all from the same year, or from different harvests? Was it the product of local farmers or a regional storage centre?
One way to answer these questions is to look at the wheat grain's carbon stable isotopes. Not all carbon atoms are the same: in nature the vast majority of carbon is 12C, the light variety, but about 1 per cent is the heavier 13C. The other carbon isotope is the unstable 14C, which is often used to date organic materials.
The exact proportion of 13C and 12C in plants depends on the environment, amount of water available and climate and can be used to learn more about past environments. Stable carbon isotopes are a powerful tool and 'there is a lot of demand for this kind of study in archaeology,' says geologist Dr Tim Heaton, from the Natural Environment Research Council Isotope Geosciences Laboratory, who joined forces with the archaeologists for this project.
But to draw conclusions about past environments it's not enough to measure old 13C/12C ratios. 'The present is the key to the past in geology and in archaeology too,' says Heaton. 'We need to understand modern carbon ratios to interpret old ones correctly.'
Carbon ratios, old and new
The team measured the carbon isotope ratio of the charred wheat from Assiros Toumba and recent wheat grains from different locations. The modern samples were harvested from areas where environmental variables are well known, so their isotope ratios 'provide a framework that can be used to interpret the past,' says Heaton.
The analyses of the old wheat grains show that the carbon isotope ratios are very similar and the differences are within the natural variations observed in a single modern wheat field. The lack of variation suggests that all the wheat in Assiros Toumba comes from a single year's harvest gathered over a small area, write the authors in the report published this week in the Journal of Archaeological Science.
The ancient carbon isotope ratios also suggest that the Assiros Toumba wheat grew with plenty of water. As there is no evidence for higher rainfall during the Bronze Age, the findings suggest that the crops were well watered by the farmers, who also kept the fields free from weeds that might have competed with the wheat for moisture.
The results help to provide a better understanding of farming practices in the Assiros Toumba region during the Bronze Age. Farmers kept intensive, well-watered and weed free wheat fields and stored the harvest in communal storage rooms, perhaps controlled by ruling elites.
Tim H.E. Heaton, Glynis Jones, Paul Halstead, Taxiarchis Tsipropoulos. Variations in the 13C/12C ratios of modern wheat grain, and implications for interpreting data from Bronze Age Assiros Toumba, Greece. Journal of Archaeological Science. Available online 21 June 2009
Interesting? Spread the word using the 'share' menu on the top right.