Wall discovered in central Greece could be world’s oldest

The unassuming remains of a stone wall that once partly closed off the entrance to the prehistoric Theopetra Cave near Kalambaka, Thessaly, have recently been dated by specialists to about 21000 BC, making it the oldest known man-made construction in Greece and likely the world, according to a statement on March 22, 2010, by the Greek Ministry of Culture and Tourism. According to radio carbon dating, the date 23,000 BP (years before present) was determined by a pair of scientists, Nicholaos Zacharias and Ioannis Basiakos, at the Archaeometry Laboratory of the National Center for Scientific Research Demokritos, using a relatively new method of dating called Optically Stimulated Luminescence (OSL, see below).

The cave, in a setting overlooking the Lithaios River, a tributary of the Pineios River, just 3 kilometers from the rock pillars and monasteries of Meteora, consists of a 500-square-meter rectangular chamber of which the entrance is 17 meters long by 3 meters high. The reported wall, constructed of dry masonry, extends across the cave?s mouth reducing the large opening by about two-thirds. The wall?s suggested date coincides with the last glacial period (circa 110,000-10,000 years ago) and indicates that the structure may have been built by Paleolithic inhabitants of the cave to protect themselves against the bitter cold.

The Theopetra Cave, only open to the public since last September, has been the subject of systematic multidisciplinary archaeological excavations conducted since 1987 by Dr Nina Kyparissi-Apostolika, director of the Ephorate of Paleoanthropology and Speleology of Southern Greece. Inside was found a 6-meter-deep stratified sequence of archaeological deposits that indicate the cave was continuously inhabited from circa 50000 BC to 3000 BC ? that is, from the later Middle Paleolithic (circa 300,000-40,000 years ago) through the Upper Paleolithic (40,000-12,000 years ago), the Mesolithic (12,000 years ago to start of Neolithic) and the Neolithic (6000-3000 BC in Thessaly) periods. Evidence of temporary use during the Bronze Age was also discovered, while in modern times shepherds and other transient visitors occasionally occupied the cave right up to the time excavations began in 1987. The chronology of its prehistoric inhabitation has been established through more than 50 radiocarbon dates derived mostly from charcoal samples collected from the remains of hearths.

Apart from its extraordinary length of inhabitation ? longer than that of the southern Argolid?s Franchthi Cave ? the Theopetra Cave is also unique in Greece because its archaeological record spans two great moments in human history: the replacement of Neanderthals by modern humans (circa 30,000 years ago) and the shift in human subsistence from nomadic hunting and gathering to sedentary farming that marks the start of the Neolithic era. The Theopetra Cave also provides the earliest evidence for Paleolithic cave dwelling in Thessaly and an important record of climatic change during the late Pleistocene and early Holocene eras.

Long before the cave was inhabited, it seems that Neanderthals were already aware of its existence. In March 2009, Kyparissi-Apostolika?s team found a trail of at least three hominid footprints left in the cave?s soft earthen floor ? apparently by several Neanderthal children about 2-4 years old, judging by the prints? sizes ? during the Middle Paleolithic period about 135,000 years ago.

The ongoing investigation of the Theopetra Cave involves many different specialists, including archaeologists, geologists, paleobotanists and zooarchaeologists. The rich array of materials thus far recovered by these scientists consists of charcoal; stone tools; pottery; bone, stone and shell objects, including bracelets and beads; ceramic figurines and human remains in various burials dated to circa15000 BC, 9000 BC and 8000 BC. Analysis of carbonized plants and seeds has also begun to shed light on the inhabitants? dietary practices. Deposits of unbaked clay detected within the cave point to Upper Paleolithic exploitation or experimentation with the malleable material long before actual fired pottery began to appear in the early Neolithic era.

What is OSL?

Mineral-rich sediments such as those deposited over thousands of years in the Theopetra Cave can be an important source of information for specialists trying to pinpoint when a prehistoric archaeological site was inhabited. Optically stimulated luminescence (OSL), invented in 1984 at Simon Fraser University in Canada, is considered a valuable Quaternary dating method for a variety of aeolian, fluvial, marine and colluvial sediments. OSL involves beaming sediment samples with blue, green or infrared light to determine how long ago minerals including quartz and feldspar were last exposed to daylight. Samples subjected to such treatment may emit a luminescence whose intensity can be an indicator of how much radiation (in part from cosmic rays) the sample absorbed during its burial. The older a sample is, the more luminescence it emits. To determine age, a comparison is made between sediments with a known amount of added radiation and sample sediments that were affected naturally. Exposure to sunlight resets the luminescence signal, thereby allowing the time period since the soil was buried to be calculated. Optical dating is unsuitable for sediments older than 500,000 years and those deposited with little or no exposure to daylight (such as sediments inside dark caves). Furthermore, the collection of samples must be conducted with care, since the OSL technique is sensitive to light contamination. The amount of moisture that has infiltrated sample sediments since their deposition is also critical to the accuracy of the dating process. Although OSL has only been in existence for 25 years and remains in development, it represents an important new dating method and a valuable addition to the archaeologist?s toolkit.

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