Scientists solve the origin of Stonehenge’s sarsen stones
Most of Stonehenge's megaliths, called sarens, came from West Woods, Wiltshire.
- Researchers have known Stonehenge's smaller bluestones came from Preseli Hills, Wales, but the source of its sarsens has remained a mystery.
- Using chemical analysis, scientists found a matching source at West Woods, approximately 16 miles north of the World Heritage Site.
- But mysteries remain, such as why that site was chosen.
Many mysteries surround Stonehenge. Who built it and what purpose did it serve? Why that arrangement of megaliths and lentels? How did Neolithic people move and erect such massive stones using 5,000-year-old technology? Because Stonehenge's builders left us no written record, historians, archaeologists, enthusiasts, conspiracy theorists, and outright cranks have tried for centuries to translate their prehistoric silence into answers.
As scientific tools and techniques have advanced, we've learned to better discern the forensic clues left behind in the megaliths, inhumed bodies, and landscape of the Salisbury Plain. Today, scientists have traced Stonehenge's "bluestones"—smaller dolerite stones found in the monument's interior—to quarries in Preseli Hills, Wales. They've also established that the bluestones likely served as grave markers for the people buried there, also from Wales.
Thanks to our scientific tools, and a reclaimed piece of history, another Stonehenge mystery has been solved. Scientists have pinpointed the source area for most of the monument's extant sarsens. And no, aliens did not carry these megaliths with tractor beams to create an interstellar landing pad. Sorry, cranks. Stonehenge's origin is far more terrestrial, found in a little spot near Marlborough Downs.
Discovering Stonehenge's signature
In 1958, engineers undertook the task of re-erecting a Stonehenge trilithon that fell in 1797. Three cores drilled into a sarsen disappeared soon after.
"Sarsen" is the common term for the giant sandstone—more specifically, duricrust silcrete—megaliths that enwreathe Stonehenge. Fifty-two of an estimated 80 sarsens remain today. They form both the interior horseshoe and the uprights and lintels of the outer circle, as well as peripheral stones like the Heel and Slaughter Stones. The largest sarsens stand at about 30 feet tall and weigh around 25 tons.
The immense size of these boulders sits at the center of one of Stonehenge's most enticing enigmas. How did people, using only Neolithic technology, manage to move and prop up such massive stones? A major piece to that puzzle has been their source, as the answer would inform scientists on the opportunities and challenges facing the builders as they moved the sarsens.
To find that piece, David Nash, the study's lead author and a professor at Brighton University, and his team analyzed the sarsens using a portable X-ray fluorescence spectrometer. This non-intrusive analysis allowed them to generate initial chemical characterizations for the stones' 34 chemical elements.
"Until recently we did not know it was possible to provenance a stone like sarsen," Nash said in a release. "It has been really exciting to use 21st century science to understand the Neolithic past and answer a question that archaeologists have been debating for centuries."
To further hone in on the source area, the team needed to generate high-resolution chemical signatures by analyzing a sample. Of course, the idea of tearing a sample out of this World Heritage Site would be near sacrilege. Luckily, a previously lost piece of history had recently been returned to the British people.
In 1958, a restoration program re-erected a Stonehenge trilithon that fell in 1797. After lifting the sarsens, engineers discovered cracks in one of the uprights (Stone 58). They drilled out three cores from the stone and inserted metal ties to reinforce its integrity. The holes were filled with sarsen plugs to hide the intrusion. However, the three cores disappeared.
Flash forward to 2018. Robert Phillips, an 89-year-old U.S. citizen and on-site worker during the restoration, returned one of the three cores. Nash and his team were granted permission to sample a piece from "Phillips' core." They used a plasma mass spectrometer to create a chemical signature for the monument, one they could compare to potential source sites across southern Britain.
They found a match in West Woods, Wiltshire. Fifty of Stonehenge's 52 sarsens share a chemical signature with the stones in this area, strongly suggesting they were sourced there. The area also sports a high concentration of evidence for early Neolithic activity, adding to its plausibility.
"To be able to pinpoint the area that Stonehenge's builders used to source their materials around 2,500 BC is a real thrill," Susan Greaney, senior properties historian at English Heritage, told the BBC. "While we had our suspicions that Stonehenge's sarsens came from the Marlborough Downs, we didn't know for sure, and with areas of sarsens across Wiltshire, the stones could have come from anywhere."
She added the evidence showed "how carefully considered and deliberate the building of this phase of Stonehenge was."
The study was published in Science Advances.
For every answer, another question
A view of Stonehenge during the Summer Solstice.
(Photo: Wikimedia Commons)
Thanks to Nash and his team, scientists now know the source of Stonehenge's sarsens. This clue can help them solve other Stonehenge mysteries. That most of the stones were sourced from one location, the study notes, suggests that they were erected at about the same time. It also reveals the routes the Neolithic builders had to traverse with their heavy loads.
But questions remain. Why did the builders choose West Woods when the Salisbury Plain is dense with sarsen? Why were two megaliths (Stones 26 and 160) sourced elsewhere? And were the missing stones gathered from West Woods or elsewhere?
These questions only touch on the sarsens. The question that intrigues so many of the monument's visitors remains hotly debated: Who built Stonehenge and why? Was it a burial site for the Stone age elite? A monument marking British unification? A Druid Mecca? We don't know, but as scientific tools advance, we may be able to break the prehistoric silence that has laid over Stonehenge for so long.
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The idea of 'absolute time' is an illusion. Physics and subjective experience reveal why.
- Since Einstein posited his theory of general relativity, we've understood that gravity has the power to warp space and time.
- This "time dilation" effect occurs even at small levels.
- Outside of physics, we experience distortions in how we perceive time — sometimes to a startling extent.
Physics without time<p>In his book "The Order of Time," Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.</p><p style="margin-left: 20px;">"If I observe the microscopic state of things," writes Rovelli, "then the difference between past and future vanishes … in the elementary grammar of things, there is no distinction between 'cause' and 'effect.'"</p><p>So, why do we perceive time as flowing <em>forward</em>? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.</p><p>Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.</p><p style="margin-left: 20px;">"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the <a href="https://www.ft.com/content/ce6ef7b8-429a-11e8-93cf-67ac3a6482fd" target="_blank"><em>Financial Times</em></a>. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."</p>
The strange subjectivity of time<p>Time moves differently atop a mountain than it does on a beach. But you don't need to travel any distance at all to experience strange distortions in your perception of time. In moments of life-or-death fear, for example, your brain would release large amounts of adrenaline, which would speed up your internal clock, causing you to perceive the outside world as moving slowly.<br></p><p>Another common distortion occurs when we focus our attention in particular ways.</p><p style="margin-left: 20px;">"If you're thinking about how time is <em>currently</em> passing by, the biggest factor influencing your time perception is attention," Aaron Sackett, associate professor of marketing at the University of St. Thomas, told <em><a href="https://gizmodo.com/why-does-time-slow-down-and-speed-up-1840133782" target="_blank">Gizmodo</a></em>.<em> "</em>The more attention you give to the passage of time, the slower it tends to go. As you become distracted from time's passing—perhaps by something interesting happening nearby, or a good daydreaming session—you're more likely to lose track of time, giving you the feeling that it's slipping by more quickly than before. "Time flies when you're having fun," they say, but really, it's more like "time flies when you're thinking about other things." That's why time will also often fly by when you're definitely <em>not</em> having fun—like when you're having a heated argument or are terrified about an upcoming presentation."</p><p>One of the most mysterious ways people experience time-perception distortions is through psychedelic drugs. In an interview with <a href="https://www.theguardian.com/books/2018/apr/14/carlo-rovelli-exploding-commonsense-notions-order-of-time-interview" target="_blank"><em>The Guardian</em></a>, Rovelli described a time he experimented with LSD.</p><p style="margin-left: 20px;">"It was an extraordinarily strong experience that touched me also intellectually," he said. "Among the strange phenomena was the sense of time stopping. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing any more. It was a total subversion of the structure of reality."<br></p><p>It seems few scientists or philosophers believe time is completely an illusion.</p><p style="margin-left: 20px;">"What we call <em>time</em> is a rich, stratified concept; it has many layers," Rovelli told <em><a href="https://physicstoday.scitation.org/do/10.1063/PT.6.4.20190219a/full/" target="_blank">Physics Today</a>.</em> "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."</p>What <em>is</em> an illusion is the idea that time flows at an absolute rate. The river of time might be flowing forever forward, but it moves at different speeds, between people, and even within your own mind.
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