快猫短视频

Fossilised piles of faeces, called middens, have revealed that a desert valley in Yemen was once a tropical oasis, which聽may have lasted in the dry region because of human land management practices.

Today, Wadi Sana is a dry, rocky desert. We knew that between 11,000 and 5000 years ago, the Arabian peninsula and Sahara desert were wetter than they are now, and some lake-bed deposits suggested that grasslands and trees may have聽grown elsewhere in the interior of the peninsula.

To find out more, at Pennsylvania State University and her colleagues turned to the petrified faeces of rock hyraxes (Procavia capensis). These small herbivorous mammals are native to parts of Africa and the Arabian peninsula and, despite their rabbit-like appearance, are kin to elephants and sea cows.

Hyraxes live in colonies, defecating and urinating in a聽communal latrine. Many generations of them may inhabit the same location, and the layers of their concentrated waste material petrify in the dry air, creating a time capsule of local habitats because pollen and plant material are preserved聽in the faeces. Some聽hyrax middens date聽back聽50,000 years.

鈥淔ew other archives of information about past environments exist in dry聽places,鈥� says Ivory.

The researchers collected 24聽middens in Wadi Sana, using聽a chemical dating process on 17聽of them. The team also extracted fossilised pollen from 14 of these and classified it using a microscope. The pollen record shows that between 6000 and 4700 years ago, Wadi Sana was home to abundant tropical woodlands totally unlike anything there today.

The region harboured frankincense and olive trees, as well as buttontrees (Terminalia), which today mostly grow along the foggy coastline. Elsewhere in the region, ecosystems were drying out and turning to desert as the monsoons weakened. But Wadi Sana was something of an oasis, partially thanks to the buttontrees that draw moisture from the air and pump it into the ground, but also because of the humans that moved there.

Archaeological evidence shows humans living and raising cattle in Wadi Sana from聽roughly 8000 to 5000 years ago. As monsoon rains grew unreliable, they dammed local waterways. This may have extended the life of the oasis by creating a wetter microclimate in the face of Arabia鈥檚 drying.

鈥淗uman management actually acted to make this woodland and all of its associated benefits more resilient to climate change instead of less resilient,鈥� says聽Ivory.

An increase of charcoal in the聽midden record suggests that聽people eventually started burning the landscape more frequently to encourage new grass growth to feed cattle, which changed the local plant composition and may have shrunk the woodlands. Later still, the decrease in rainfall and abandonment of dams appears to have culminated in Wadi Sana鈥檚 transformation to desert.

鈥淭here is a real need for fossil聽records with a good chronological framework in all hyper-arid areas鈥�, such as these hyrax middens, says at the University of Montpellier in France, noting that the middens鈥� typical location deep in rock shelters makes them difficult to find. 鈥淭he hyraxes chose their habitats to protect themselves from predators, and apparently from scientists, too.鈥�

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