快猫短视频

Early farmers living in Turkey increased their reliance on domestic sheep and goats over a period of 1000 years. The shift in practices has been revealed by the animals鈥� urine, which is preserved in the soil as distinctive salts.

鈥淔or the first time, we can get a quantitative estimate of the number of organisms it would take to produce these salts,鈥� says geochemist Jordan Abell of Columbia University in New York. This offers an idea of the herd sizes at the time, he says.

Abell and his colleagues studied a Stone Age site called As抬谋kl谋 H枚y眉k in Turkey, which was discovered in the 1960s and has been excavated on and off since the 1980s. It was occupied between about 10,400 and 9300 years ago. The people living there built oval houses of wattle and daub, which were closely packed together.

As抬谋kl谋 H枚y眉k is one of many places in and around the Middle East where people gradually abandoned hunter-gathering to focus on farming. Previous excavations have revealed an increasing reliance on sheep and goats for meat, . Crops including were important too.

To track the growth of the animal herd, the team studied salts rich in sodium, chlorine and nitrate, which were preserved in the layers of sediment. Most of these salts seem to have come from urine, either from humans or their domestic animals.

The team first subtracted other potential contributors, such as wood ash. Then they looked up how much the average human or sheep urinates per day. The question, says Abell, was: 鈥渉ow many organisms would it take to produce that much salt?鈥�

Dense herd

The team tracked the preserved urine through four layers of sediment, which span 1000 years of occupation. This allowed them to estimate how many large animals (including humans) lived in As抬谋kl谋 H枚y眉k at different times.

The number rose only slowly from the oldest layer to the second oldest, but then leapt up in the third layer, reaching a population density of one organism for every 10 square metres. That is about half the density recommended for modern sheep breeders, indicating a fairly dense herd.

By factoring in the size of the mound, they were able to estimate the total population. 鈥淵ou鈥檇 need about 1800 organisms peeing on the mound to produce these salts,鈥� says Abell. Some of those organisms will have been people, but even so there seem to have been at least several hundred sheep and goats, he says.

鈥淚t鈥檚 very likely that they were poor animal managers,鈥� says Abell. 鈥淓arly on they probably stuck them between buildings, and they didn鈥檛 even get to go out in pasture.鈥� In the top level, the salt concentrations 鈥� and therefore the population density 鈥� falls slightly. Abell suspects this is because the people had begun moving their animals to the edge of the settlement and allowed them out to pasture.

The idea of studying urine salts is new and could be used to estimate population sizes at other prehistoric sites, says Abell.