A new study led by interdisciplinary team researchers at the University of South Florida and The University of New Mexico suggests humans were in Mallorca, Spain, an island in the western Mediterranean, at least 5,600 years ago.
This date is at least 1,000 years earlier than previous research has suggested and has been determined by calculating when a now-submerged ancient bridge on the island could have been constructed. Mallorca is one of the larger islands in the Mediterranean Sea and is thought to have been amongst the last of the islands in the area to be colonized. Previous research suggests a timeframe for the earliest settlement of the island of between 4,600 and 4,200 years ago. Some early evidence indicated a potential human presence on the island as far back as approximately 9,000 years ago, although this is 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.
The research, 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, revised the timeframe for human arrival by calculating when an ancient, submerged bridge in Genovesa Cave, Mallorca, could have been constructed.
By studying the 25-foot submerged bridge, the researchers were able to provide compelling evidence of earlier human activity inside Genovesa Cave, located in the Spanish island of Mallorca. The previously discovered bridge consists of large limestone blocks laid over each other to connect two elevated chambers of the cave. It has a distinct coloration mark on its upper section, which the researchers suggest was caused by calcite formation at the 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 the U-series method, a radiometric dating technique used to determine the age of calcium carbonate materials such as cave formations, the researchers dated the samples to determine that humans may have first arrived on Mallorca between 6,000 and 5,600 years ago, over 1,000 years before the previous consensus timeline.
The researchers compared the vertical position of the bridge and the height of the coloration mark to a model of relative sea level in the area for the Late Holocene. They found that the bridge was unlikely to have been constructed much more than 6,000 years ago because the area it spans would not have been underwater and there would have been no need for a bridge.
Additionally, the stone bridge had probably been constructed approximately 5,600 years ago, as after this time, the sea level would have risen above the top of the bridge. The coloration mark on the bridge could have formed during stable sea levels between these two dates in the model. This group of researchers published a paper in 2022 reporting a very stable relative sea level very near the present sea level in Mallorca for the last 4,000 years. It shows that the bridge would have been submerged during this time.
"POS are remarkable sea-level indicators, and combined with our dating, we could tell within a few hundred years of when the bridge was constructed. It is a very novel and accurate way to push back when people were in Mallorca. The sea level research in Mallorca using speleothems is truly incredible and exciting. This study also shows how special POS is as a scientific sea-level tool. Perhaps our results will encourage further research on this subject," said Polyak. "Both of us are glad to be part of this NSF-funded study. We have a Ph.D. student here at UNM who is part of new sea-level studies that includes another island in the Mediterranean—Sardinia."
This study was supported by several National Science Foundation grants and 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
