麻豆淫院

Research led by Institut de Pal茅ontologie Humaine is providing a finite minimum age for a nearly complete cranium from Petralona Cave in Greece that has perplexed researchers since its discovery in 1960.

The mystery of the Petralona Cave skull centers around two intriguing unknowns. First, while it is clearly of the Homo genus, it is distinctly different from both Neanderthals and current modern humans. Next, dating the skull has remained difficult to narrow down, with previous estimates spanning about 170,000 to 700,000 years in age.

In the study, "New U-series dates on the Petralona cranium, a key fossil in European human evolution," in the Journal of Human Evolution, researchers present new U-series dates performed on the calcite that grew directly on the cranium to provide crucial information on the age of the fossil.

U-series dating takes advantage of the natural properties of uranium isotopes. Uranium breaks down into thorium at a precise half-life. By measuring the ratio of uranium to thorium it is possible to calculate when the process began, giving an atomically calibrated start date.

In soil, environmental deposits of uranium isotopes are constantly being added, making it impossible to use the U-series technique to date the dirt itself as it is a mixture of half-lives ticking away at different starting points.

But in a cave environment, that all changes. As moisture moves through soil, it carries with it water-soluble minerals, including the uranium, leaving the thorium behind. If that moisture then collects on a cave wall it can evaporate, leaving behind the trace minerals and uranium isotopes without thorium, forming a layer of crusty residue.

Within layers of these crusty deposits, the uranium isotopes continue to break down into thorium, now locked into place by the mineral deposit in a closed system, giving each layer a set date at which the process began.

U-series dating then analyzes the uranium to thorium ratios of the innermost deposit layers to determine when they first appeared, giving a minimum in situ starting point for anything found beneath.

Sampling included the calcite coating on the cranium as well as speleothems and calcitic deposits in different cave locales, the Mausoleum chamber where the cranium was reportedly cemented to a wall, the corridor leading to it, and additional sections.

Results from the calcite crust on the cranium provide a finite minimum age of 286,000 卤 9,000 years (or 286 卤 9 ka). If it initially remained dry or covered, the skull could have been in the cave much longer, as the dating technique can only determine when it began to form the calcite through moisture exposure and evaporation. To calculate the maximum timeline, the age of cave elements becomes the default parameter.

Ages from the stalagmitic veil on the Mausoleum wall yielded 510 卤 29 ka at the top and a minimum of >650 ka internally, indicating that cranium coating began well after the cave was established. Stratigraphy in the Dardanelles Passage shows no stalagmitic floor older than 410 卤 6 ka, with a younger layer dated to 228 卤 1 ka.

Age ranges derived from site relations are reported as 539鈥�277 ka if the cranium was attached to the wall, or deposition between 410 ka and 277 ka if not.

Researchers conclude that the Petralona hominin forms part of a distinct and more primitive group than Homo sapiens and Neanderthals, with results supporting the coexistence of such populations alongside an evolving Neanderthal lineage in the later Middle Pleistocene of Europe.

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