A new study led by researchers from the University of South Florida and The University of New Mexico suggests that humans were present in Mallorca, Spain, at least 5,600 years ago. This date is over 1,000 years earlier than previously thought.

The findings were determined by calculating when a now-submerged ancient bridge on the island could have been constructed. Previous research suggested that human settlement on Mallorca occurred between 4,600 and 4,200 years ago. Some early evidence indicated a potential human presence as far back as approximately 9,000 years ago, although this remains debated.

The study titled "Submerged bridge constructed at least 5600 years ago indicates early human arrival in Mallorca, Spain" was published today in the journal Communications Earth & Environment.

A diver stands on the submerged bridge central to the study. Photo credit: Robert Landreth

Led by University of South Florida Geology Professor Bogdan Onac and colleagues from The University of New Mexico—including Distinguished Professor Yemane Asmerom and Research Scientist Victor Polyak—Harvard University, and the University of Balearic Islands, the research revised the timeframe for human arrival by examining an ancient submerged bridge in Genovesa Cave, Mallorca.

By studying the 25-foot submerged bridge made of large limestone blocks connecting two elevated chambers of Genovesa Cave, researchers provided compelling evidence of earlier human activity. The distinct coloration mark on its upper section was attributed to calcite formation at water level when the bridge was still in use.

“A type of speleothem (cave formation) called phreatic overgrowths on speleothems (POS for short) grow exactly at sea level, making them one of the most important sea-level indicators,” said Polyak. “They are made up of calcite and/or aragonite (calcium carbonate), minerals that can be accurately dated in our lab, the Radiogenic Isotope Laboratory here at The University of New Mexico. We dated the samples in this study using the uranium-series (U-series) method, which can be exceptionally accurate.”

Using U-series dating—a radiometric technique used to determine the age of calcium carbonate materials—the researchers concluded that humans may have first arrived on Mallorca between 6,000 and 5,600 years ago.

The team compared the vertical position of the bridge and height of its coloration mark to a model of relative sea level during the Late Holocene. They found it unlikely that construction occurred much more than 6,000 years ago because there would have been no need for a bridge if not underwater.

Additionally, they estimated that construction likely took place around 5,600 years ago since rising sea levels would have submerged it after this period. Their previous research reported stable relative sea levels near present-day levels for Mallorca over the last 4,000 years.

“POS are remarkable sea-level indicators,” said Polyak. “Combined with our dating methods we could tell within a few hundred years when the bridge was constructed... This study also shows how special POS is as a scientific sea-level tool.”

This NSF-funded study involved extensive fieldwork including underwater exploration and precise dating techniques.

Top photo: A diver explores Drac Cave illustrating how phreatic overgrowths on speleothems grow precisely at sea level. Photo credit: Miquel Perello