August 14, 2024
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Stonehenge’s strangest rocks came from 500 miles away
New analysis of Stonehenge’s “altar stone” suggests that Neolithic people walked or sailed around 500 miles to transport the six-tonne rock.
Shana Baker/Getty Images
One of the giant rocks at Stonehenge, a mysterious structure in southern England, may have been transported from nearly 500 miles away — an incredible feat that occurred about 4,500 years ago.
Known as the “Altar Stone,” this 16-foot-long, 6-ton slab of gray-green sandstone sits at the center of the site’s inner circle. Archaeologists have long speculated that it, like other so-called bluestones, was transported to the site from west Wales. “It’s just one of those long-standing hypotheses that no one has actually tested,” says David Nash, a geographer at the University of Brighton in the UK, who has analyzed other rocks at Stonehenge.
But a new study published on August 14th found that NatureScientists have tested the hypothesis and come to a surprising conclusion: the altar stone appears to have come from northeast Scotland, which is much further from Stonehenge than Wales and in the opposite direction. Still, it remains a mystery as to who transported it to Stonehenge, how it got there, and how long the journey took. Researchers say that Stonehenge’s builders could have tracked it down and brought it back by boat, or Scottish residents could have transported it south overland during their own visit to the site, or it could have arrived by some other means altogether.
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Stonehenge’s altar stone is buried underground and largely covered by two fallen sarsen stones.
Professor Nick Pearce, Aberystwyth University
To pinpoint the altar stones’ origins, scientists analyzed three types of minerals found in the sandstone, which forms when tiny particles erode from local mountains, become sediment, and are eventually compressed into rock. These rock particles contain brittle minerals called apatite and rutile, which tell scientists about recent geology, and zircon, an ultra-tough mineral that allows researchers to peer into the past billions of years ago.
As zircon, apatite, and rutile crystals form, tiny amounts of radioactive uranium become incorporated into their structure. That uranium decays at a known rate into lead. By measuring the ratio of uranium to lead, scientists can calculate when a rock grain formed. Reproducing this process for many grains in a slab of rock gives researchers a kind of unique “fingerprint” that dates those grains.
The new analysis finds that Alterstone’s mineral age signature doesn’t match that of rocks in southern England and Wales, where rocks are typically made up of much younger minerals, but its profile resembles that of a rock formation called the Orcadian Basin, which is exposed throughout a swath of Scotland to islands off the northeast coast.
The analysis wasn’t comprehensive enough to determine where exactly the altar stones came from, and the researchers hope to address this question in future studies by collecting samples from across the Auckland Basin and comparing them with the Stonehenge data, as well as analysing additional minerals to flesh out each rock’s story.
The new study is strictly based on geology, and the authors don’t offer any hypotheses about why the ancient builders transported such large rocks over such long distances, or how they accomplished the feat. It may simply have been a matter of geological understanding. “Humans have always been fascinated by finding the perfect rock, and maybe the Neolithic Britons were no different,” Anthony Clark, a doctoral student at Curtin University in Australia and co-author of the new study, said at a recent press conference.
But those theories will surely emerge.
“Now that the geology has been explained, I’m excited to see what my colleagues think about the archaeology,” says Heather Sevier, an archaeologist who was not involved in the study and is senior asset manager for Stonehenge at English Heritage, the site’s manager.
The researchers say they didn’t expect the rocks to be Scottish, but Sevier and Nash say they aren’t surprised, given known trade routes for portable artefacts like pottery and axes at the time. “It’s not that shocking that there was that level of communication and connection,” Nash says. “If they’re prepared to bring stones from Wales to Stonehenge, it’s not that far-fetched to bring stones from other parts of the British Isles to Stonehenge.”
For Sebile, the find shows that Stonehenge has long retained the fascination and iconic status that makes it the site it is today. “Today, people from all over the world visit Stonehenge. It’s a magnet for people,” Sebile says. “My impression is that back then the idea was probably the same, that people wanted to come and contribute.”
