Sure enough, the fluctuating levels of urine salts revealed the history of human and animal occupation of Aşıklı Höyük. Very little salt was detected in the natural layers, before any settlement existed. Between about 10,400 and 10,000 years ago, salt levels rose slightly, as a few humans began settling. Then things really took off – between 10,000 and 9,700 years ago the salts saw a huge spike, with levels about 1,000 times higher than previously detected. That indicates a similar spike in the number of occupants. After that, concentrations go into decline again.
That large spike, the team says, suggests that domestication of animals in Aşıklı Höyük occurred faster than was previously thought.
Using this data, the researchers estimated that over the 1,000-year period of occupation, an average of 1,790 people and animals lived in the area per day. At its peak, the population density would have reached about one person or animal for every 10 sq m (108 sq ft).
The estimated inhabitants of each time period can’t be all human – the houses found on site indicate a smaller population. But the team says this is evidence that salt concentrations can be a useful tool to study the density of domesticated animals over time.
The researchers say this technique could be used in other sites, to help find new evidence of the timing and density of human settlement.