A submerged bridge in a cave on Mallorca’s coast has revealed a new story of ancient settlement on the island—one that drastically alters our ideas about human history in that part of the world.
A study published today (Friday, August 30) has concluded that humans settled on the Spanish island much earlier than previously thought—at least 5600 and possibly even 6000 years ago (around 4000BC), making prior estimates at least 1000 years off the mark.
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The study, which featured in the Communications Earth & Environment journal, helps resolve a longstanding paradox. It always puzzled researchers that the large Spanish islands close to the mainland appeared to have been colonized much later than the smaller islands further away in the Mediterranean. After all, why would you sail by leaving them untouched?
“It was kind of strange for me to think there was such a huge gap between [the colonization of] this group of islands and others,” the study’s lead author Bogdan Onac, a geology professor at the University of South Florida, told VICE.
The story begins with Onac and his team discovering a hidden limestone bridge in the Genovesa Cave while diving there in 2000. Most of the cave is now underwater because of rising sea levels, but it wasn’t always the case.
Although Onac emphasizes he’s no archeologist, his team speculate that a pool in the cave may have been a source of water for ancient people, while poultry and goat bones found there indicate that the cool cave may once have been used to keep food out of the harsh island heat.
Despite being a heavily studied region, there has been disagreement about when people first settled in this part of the Mediterranean, known as the Balearic Islands. Early radiocarbon dating of what was thought to be human bone fragments predicted that people may have been living there 7000 years ago (around 5000BC), but the bones were later discovered to be from a cow. More recent evidence has put the settlement date at between 4600 and 4200 years in the past.
This latest study analyzed a light coloured band on the upper part of the bridge, which researchers compared to a bathtub ring showing where water used to sit. This, together with data on sea levels during the Late Holocene (the current period of time starting around 11,700 years ago) gave researchers a rough date range for human settlement.
The bridge had to be built at some time between when sea levels were so low that a bridge wasn’t needed (around 6000 years ago) and when the bridge became partially submerged—AKA when the bathing ring formed between 5964 and 5359 years ago.
Researchers confirmed the timing by dating phreatic overgrowth, a crust that can form on the spear-like natural structures hanging from cave roofs and jutting up from cave floors.
Known as Speleothems—and a general term for structures like stalactites—these form when the cave is filled with air but can become encrusted with other minerals when the cave floods. “We found the encrusted stalactites at a depth that corresponds to the coloration mark on the bridge,” explained Onac. “The pieces of data have to coexist, allowing us to reconstruct the timeline.”
It’s still unclear when other islands in the Balearic region were settled. Onac says they need to find evidence, similar to the bridge, to be able to draw any conclusions. He believes it’s likely that Mallorca was settled first because of its size and geography.
Onac and his team has been studying the caves for more than two decades, and say their work has another important takeaway: the ravages of climate change. Since they started their research, the sea level in the cave has risen upwards of another five centimeters.
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