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An ancient bridge, submerged in a cave on the Spanish island of Mallorca is helping researchers determine when people settled on islands across the Western Mediterranean thousands of years ago.
New analysis of the 25-foot-long (7.6-meter-long) bridge inside the Genovesa Cave has revealed that Mallorca, one of the largest islands in the Mediterranean, was inhabited much earlier than previously believed. The results could narrow the gap between when people settled in the eastern and western Mediterranean regions.
A study detailing the findings was published Friday in the journal Communications Earth & Environment.
Due to the lack of written records and limited archaeological evidence it is difficult to piece together the point at which people colonized and settled the Mediterranean islands.
But a “bath ring,” along with mineral formations detected on the bridge, allows scientists to estimate that the structure was built nearly 6,000 years ago, said lead study author Bogdan Onac, a professor at the School of Geosciences at the National University of Ireland. South Florida.
“The presence of this sunken bridge and other artifacts indicates a sophisticated level of activity, suggesting that early settlers recognized the cave’s water resources and strategically constructed infrastructure to navigate it,” said Onac.
A mysterious cave
The bridge is made of large, heavy limestone blocks, some 4.2 feet (1.3 meters) across, and it is still unclear what mechanisms enabled ancient people to build the bridge.
Researchers believe that those who built the bridge wanted a dry, continuous path to connect the cave entrance to a room beyond a lake inside the cave.
The cave bridge was first discovered in 2000. A few years later, a study written in Catalan estimated that the 3,500-year-old bridge was based on pottery found in one of the cave’s rooms.
Since then, research has shown that there may have been a human presence on the island 9,000 years ago with radiocarbon dating of bones and pottery on the island, but due to the poor preservation of the materials researchers put that timeline in question
More recent research studying ash, bones and charcoal on the island suggests that people settled there around 4,440 years ago.
But after studying sea level rise over other islands and the geological footprints that sea level rise may leave behind, Onac and his colleagues took a different approach.
“It was only in the last four years that we finally gathered the data needed to address this long-standing research topic and better estimate when people arrive in Mallorca,” said Onac.
Today, the passages of Genovesa Cave are still flooded as global sea levels rise.
Onac and his colleagues studied a light-colored band on the submerged bridge within the cave as well as exploring calcite that formed on the bridge during times when the sea level was higher and filled the cave.
The excavations are speleothems, or geological formations that result from the accumulation of mineral deposits over time in caves.
By reconstructing historical local sea levels and analyzing the color band on the bridge as well as the mineral deposits, the team determined that the bridge was assembled around 6,000 years ago.
The color band coincided with the formation of mineral deposits when the sea level was stagnant, indicating that it must have been built earlier than 5,600 years ago, Onac said.
Retrace ancient steps
The bridge was probably used for 400 to 500 years before rising sea levels caused the cave lake to cover the bridge, Onac said.
The team does not have clear evidence of how ancient people used the cave, but they do remember several cases.
Cave divers have discovered the fossil remains of an extinct species of goat that once lived on the island called Myotragus balearicus. They also discovered pottery inside a drive room connected to the cave entrance at the bridge, Onac said.
“This suggests that people may have used the area near the cave entrance, a large drop chamber, for living,” said Onac. “The purpose of crossing the lake to gain access to that room is not yet clear; it could be a sanctuary, a place of ritual, or a place of storage, keeping food out of Mallorca’s hot days.”
There is evidence of small stone houses and structures made of large stones in Mallorca between 2,000 and 4,500 years ago. So the cave bridge is probably a precursor to the larger and more sophisticated stone works found on the island, said Onac.
Paleontologists are still trying to determine why Mallorca was settled later than the eastern Mediterranean. Although it is large and relatively close to mainland Spain, the island had a hot, dry climate with thin soil for farming. And apart from native fish and goats, Mallorca lacked natural resources.
“In contrast, other islands had more favorable environmental conditions and abundant resources, such as minerals and livestock, which made them more attractive to early settlers,” said Onac.
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