An ancient, submerged bridge discovered in a cave on the Spanish island of Mallorca is providing researchers with crucial information about the timeline of human settlement across the western Mediterranean Sea, CNN reports.

New analysis of the 25-foot-long bridge inside Genovesa Cave indicates that humans inhabited Mallorca much earlier than previously thought. These findings could help bridge the knowledge gap regarding the timelines of human settlements in the eastern and western Mediterranean regions, according to the report.

A study detailing the findings published Friday in the journal Communications Earth & Environment.

A lack of written records and limited archaeological evidence have made it difficult to piece together the point at which humans colonized and settled on the Mediterranean islands.But a telltale “bathtub ring,” along with mineral formations detected on the bridge, has allowed scientists to estimate that the structure was built nearly 6,000 years ago, said lead study author Bogdan Onac, a professor in the School of Geosciences at the University of South Florida.

“The presence of this submerged bridge and other artifacts indicates a sophisticated level of activity, implying that early settlers recognized the cave’s water resources and strategically built infrastructure to navigate it,” Onac said.

 

A mysterious cave

The bridge is made of large, heavy limestone blocks, some of which span 4.2 feet across, and it remains unclear what mechanisms enabled ancient humans to build the bridge.

Researchers believe that those who built the bridge wanted a dry, continuous path to connect the cave’s entrance with a chamber beyond a lake within the cave.

The cave’s bridge was first discovered in 2000. A few years afterward, a study written in the Catalan language estimated the bridge to be 3,500 years old based on pottery found in one of the cave’s chambers.

Since then, research that radiocarbon-dated bones and pottery on Mallorca suggested a human presence may have been on the island 9,000 years ago, but poor preservation of the materials led researchers to question that timeline.

More recent research studying ash, bones and charcoal on the island suggests humans settled there about 4,440 years ago.

But having studied the rise of sea levels across other islands and the geologic footprints that sea level rise can leave behind, Onac and his colleagues took a different approach.

“It was only in the past four years that we finally gathered the data needed to address this longstanding research topic and better estimate the arrival time of humans in Mallorca,” Onac said.

Today, Genovesa Cave’s passages remain 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 calcite encrustations that formed on the bridge during times when the sea level was higher and filled the cave.

The encrustations are speleothems, or geologic formations that result from mineral deposits accumulating over time in caves.By reconstructing historic local sea levels and analyzing the coloration band on the bridge as well as the mineral deposits, the team determined that the bridge was assembled about 6,000 years ago.

The color band matched the same level where mineral deposits formed when the sea level was at a standstill, indicating it must have been constructed earlier than 5,600 years ago, Onac said.

 

Rediscovering Historic Trails

The bridge is believed to have been in use for up 500 years before rising sea levels submerged it beneath the lake in the cave, according to Onac. Although the team lacks definitive evidence on how ancient humans used the cave, they have oultined several hypotheses. Cave divers have uncovered fossil remains of an extinct goat species, known as Myotragus balearicus, that once inhabited the island, as well as pottery within a driving chamber linked to the cave entrance by the bridge. Onac notes that there is also evidence of small stone homes and large stone structures in Mallorca dating back 2,000 to 4,500 years, suggesting that the cave bridge may have been a precursor to the more complex stone works found on the island.

Additionally, paleontologists are investigating why Mallorca was settled later than other eastern Mediterranean islands. Despite its size and proximity to Spain’s mainland, the island had challenging weather conditions, with its hot, dry climate and thin soil, limiting agricultural potential. Also, aside from fish and the native goats, Mallorca lacked abundant natural resources.