"Completely unexpected" finding connects Stonehenge’s 6.6-ton Altar Stone to the northernmost parts of Great Britain and possible transport by ocean.A detailed chemical study of Stonehenge's central monolith has upended understanding of the British monument's mysterious origins, suggesting one of its central stones was transported from northern Scotland.

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The findings more than triple the distance that the five-square-meter, six-ton sandstone slab might have traveled, compared to previous assumptions.

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The 5,000-year-old neolithic stone circle is a treasured part of Britain's archeological heritage, visited by more than a million people each year, a site for annual solstice celebrations and most recently the subject of a controversial climate protest.

But how the structure was built remains uncertain.

Until last year, the Altar Stone was described as a 'bluestone' despite being found to be sedimentary sandstone thought to have originated from a deposit near the Brecon Beacons in Wales.

Along with smaller dolerite and rhyolite bluestone boulders from the Mynydd Preseli deposits on the country’s west coast, it has long been thought that ancient Britons transported these rocks 140 miles to construct Stonehenge. The site also features large slabs of locally-sourced sandstone.

But a report from the University of Aberystwyth last year found the Altar Stone's composition was fundamentally different from the sandstone of Wales, with its authors predicting an origin in northern Britain.

On a recommendation from the Aberystwyth team, tiny fragments of the Altar Stone were sent to the other side of the world – Western Australia – where a PhD student at Curtin University put them under the microscope.

"Rock DNA" uncovers the origins of Stonehenge's Altar Stone

Stonehenge's large, central Altar Stone lies embedded in the earth beneath two larger sarsen sandstone blocks, which were sourced from the local Wiltshire region along with the other large upright stones that form the monument's outer circle.

But when the Aberystwyth researchers led by geologist Richard Bevins identified the possibility of a different origin for the Altar in 2023, it took a Welsh expat working on the other side of the world to fill in the gaps.

"I grew up kind of wandering those [Preseli] hills, much like, maybe, Neolithic Britons did thousands of years ago, and in some way that must have inspired me," said Anthony Clarke, a geologist originally from South Wales who currently works at Curtin University's Timescales of Mineral Systems group in Perth.

Clarke and his colleagues performed an isotopic analysis of tiny decaying uranium fragments within the Altar Stone's crystals.

This process fires a laser into the rock slivers, measuring the ratio of uranium and lead released by the stone.

Using these measurements, Clarke and colleague Chris Kirkland – a Scotsman also working at Curtin – used an extensive geological database of the UK’s rock deposits to match the Altar Stone with the Orcadian Basin, about 850 kilometers north of Stonehenge.

"By measuring the isotopic ratios of uranium and lead within these little crystals, we have miniature 'clocks'," said Kirkland.

"These clocks are very handy because they tell us about the original age of the material that was eroded to produce our sandstone (...) we can look at lots of different crystals within the Altar Stone and build up an 'age fingerprint', much like DNA. It's like DNA for our rock."

Stonehenge: a story of seafaring trade?

Hauling a six-ton rock overland for more than 1000 kilometers would have been a remarkable feat six thousand years ago.

Instead, the researchers say the Altar Stone was probably transported over water.

"We initially thought it had to have been moved by ice – it's just such a long distance for humans to transport. But if we look at ice flow directions during previous ice ages in the UK, ice was actually moving even further away from southern Britain," Clarke said.

"If you look at overland transport of the Altar Stone, they would have to have passed some formidable barriers: rivers, the heavily forested nature of prehistoric Britain, the marshy boggy landscape and the mountains standing in the way, from northern Scotland (...) which then leaves us with a marine transport route."

Clarke points to evidence of sea-based trade, shipping and social connections throughout the British Isles at the time of Stonehenge's construction as supporting the ocean transport hypothesis.

It's similar to recent studies by archaeologists that uncovered the existence of an extinct branch of the Nile. Their analysis found the extinguished channel would have passed right by the site of many of the pyramids, indicating water transport was used by the Ancient Egyptians to transport the huge quantities of stone needed for their construction.

Clarke expects the water-transport hypothesis will draw a mix of responses from the archeological community but is confident this new Stonehenge study will help focus the search for the true source of the material used at the ancient site.

"I'm sure there's going to be a mixture of amazement and perhaps skepticism," Clark said.

"But this is something we welcome going forward, to really narrow down the source of the Altar Stone, perhaps to the individual outcrop or even quarry it might have been sourced from."

The new findings were published in the journal Nature.

Edited by: Derrick Williams

Primary source:

Clarke et al (2024). A Scottish provenance for the Altar Stone of Stonehenge. Nature. https://doi.org/10.1038/s41586-024-07652-1

Additional sources:

Bevins et al. (2023). The Stonehenge Altar Stone was probably not sourced from the Old Red Sandstone of the Anglo-Welsh Basin: Time to broaden our geographic and stratigraphic horizons? Published in Journal of Archaeological Science: Reports. https://doi.org/10.1016/j.jasrep.2023.104215

Bradley, Richard (2024). Beyond the bluestones: links between distant monuments in Late Neolithic Britain and Ireland. Antiquity. https://doi.org/10.15184/aqy.2024.3

Ghoneim et al (2024). The Egyptian pyramid chain was built along the now abandoned Ahramat Nile Branch. Communications Earth & Environment. https://doi.org/10.1038/s43247-024-01379-7

(The above story first appeared on LatestLY on Aug 14, 2024 09:40 PM IST. For more news and updates on politics, world, sports, entertainment and lifestyle, log on to our website latestly.com).