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  • Thanks to Skillshare for supporting this episode of SciShow.

  • { ♪INTRO } Even if you don't know much about ancient

  • history and prehistoric monuments, you've probably heard of Stonehenge.

  • The story of this incredible structure goes back more than 5000 years, and while it was

  • certainly important to the people who built it, those architects would have had no way

  • of knowing that their creation would become world-famous.

  • These days, Stonehenge is featured everywhere, from popular movies to your friend's vacation

  • photos.

  • But if there's one thing that everyone seems to know about Stonehenge... it's that there's

  • a lot that nobody seems to know about Stonehenge.

  • The monument is surrounded by famously puzzling questions, like who built it?

  • What was it used for?

  • Who's buried beneath it?

  • And especially: How did ancient people manage to move and erect those huge stones?

  • Over the years, lots of explanations have been proposed, including lost technologies,

  • outright magic, andof coursealiens.

  • But while speculation is fun and all, Stonehenge doesn't need any help from myths and legends

  • to be cool.

  • After all, just because you understand something doesn't make it any less fascinatingand

  • there is a lot about Stonehenge we understand.

  • Archaeologists have been intensely studying this structure for more than a century, and

  • while many mysteries still remain, modern science has taught us quite a lot.

  • For centuries, visitors to Salisbury Plain in Wiltshire, England have marveled at Stonehenge

  • and tried to guess at the identity of its builders.

  • One of the earliest written suggestions came from Geoffrey of Monmouth, a bishop famous

  • for his fanciful writings on British history.

  • In the 1100s, he claimed that the monument was built by Merlin.

  • Yep.

  • The wizard Merlin, of Arthurian legend.

  • The story goes that Merlin used magic to construct Stonehenge as a monument for fallen soldiers,

  • using huge rocks that were originally carried out of Africa by giants.

  • And for a while, this was actually a pretty popular story.

  • Later scholars got more realistic, though, and proposed a list of non-fictional suspects,

  • including the Romans and the Mycenaeans from Greece.

  • And while artifacts found at Stonehenge indicate that some of those cultures did use or visit

  • the monument in its later years, recent evidence has ruled them out as its builders.

  • A lot of that evidence has come from radiocarbon dating.

  • This method is one of the most useful tools archaeologists have, because it mostly just

  • requires some radioactive carbon.

  • In nature, carbon atoms come in a few different forms, or isotopes, which have different numbers

  • of neutrons.

  • Some of these isotopeslike a key one called carbon-14 — are radioactive, so they

  • break down over time at really predictable rates.

  • By figuring out how much radioactive carbon has decayed in a material, scientists can

  • calculate how long ago the material formed.

  • And that means they can place a date on all sorts of organic substances.

  • Including ones found at Stonehenge.

  • Radiocarbon dating of human remains and artifacts has revealed that the monument's history

  • actually goes back to around 3000 BCE.

  • Which is definitely too old to have been built by the Romans or Mycenaeansor Merlin!

  • Unfortunately, whatever group made Stonehenge didn't leave behind much evidence about

  • who they were, so their identity remains a mystery.

  • And the story is complicated even more by the fact that, like many ancient landmarks,

  • Stonehenge wasn't built in a dayor even in a century.4

  • Archaeologists have identified multiple phases of construction at the site over a period

  • of about 1500 years, possibly by different groups of people.

  • The earliest construction happened around 5000 years ago, and it involved the digging

  • of the circular ditch that still surrounds the monument.

  • This formation is very similar to a type of earthwork called a henge.

  • We know this partly from carbon dating pieces of tools that were left behind.

  • But we've also found cremated human remains from this period, hiding in pits within the

  • henge.

  • It's possible that some early stones were also put up around this time, but based on

  • other evidence, it's most likely that the famous, giant standing stones didn't arrive

  • for another 500 years.

  • So, even if there isn't enough evidence to say exactly who did the heavy lifting,

  • archaeology has been able to help us understand when it happened, which has ruled out some

  • suspects.

  • MERLIN.

  • Science has also been able to help us figure out how Stonehenge was built.

  • And one thing is for sure: Getting all these rocks into place was no easy task.

  • There are two major categories of stonesalso called megalithsat Stonehenge.

  • The enormous sarsens typically weigh around 22 metric tons each, while the smaller bluestones

  • are a modest 2 to 5 metric tons.

  • Today, there are around three dozen stones at the site, arranged into two outer circles

  • and two inner horseshoes.

  • But based on the holes dug into the ground, there likely used to be more.

  • From what we can tell, workers first dug holes for the rocks to sit in, and then hauled them

  • upright, probably with the help of ropes, A-frames, and lots and lots of people.

  • The standing stones were then capped with horizontal beams to form what architects call

  • lintels, like the beam over the top of a doorway.

  • These were probably lifted up there on wooden platforms that were dismantled after construction.

  • But these lintels weren't just plopped down.

  • Holes, tabs, and joints were carved into the rocks so that the architects could insert

  • Tab A into Slot B and fit them all together, like a very heavy piece of IKEA furniture.

  • Admittedly, this is some very advanced engineering for that time period, but unlike what a lot

  • of Internet forums say, it's not impossible.

  • The builders might have lived a few thousand years before cranes and power tools, but they

  • still had that good old fashioned human ingenuitywhich we tend to overlook.

  • Also, never underestimate the power of a good ramp and pulley system.

  • Archaeologists think major work on Stonehenge continued until around 1500 BCE, and that

  • in that time, more earthwork features were dug, and the bluestones were rearranged multiple

  • times.

  • But who built the structure and how actually aren't the biggest questions scientists

  • and historians have asked.

  • Instead, the real mystery is how the stones got there.

  • See, the big sarsens are made of sandstone, and the bluestones are variously formed from

  • rhyolite, dolerite, and other types of rock.

  • But none of them match the geology of the nearby area.

  • Thankfully, no matter how far a stone has traveled, it still has the same geologic age

  • and composition as the formation it came from.

  • So, after analyzing the mineral makeup of the stones at Stonehenge, as well as determining

  • their age with other forms of radiometric dating, geologists have been able to go hunting

  • for outcrops that match its features.

  • And we think we've found some answers.

  • Although there's still plenty of debate, many scientists believe the sarsens came from

  • a region called Marlborough Downs, about 32 kilometers from Stonehenge.

  • And the bluestones most likely came from the Preseli Hills of Wales more than 200 kilometers

  • away.

  • A 2015 study from the journal Antiquity even identified a site that not only matches the

  • geology of the bluestones but also shows evidence of quarrying during the right time period.

  • The researchers have suggested this might actually be a site where Stonehenge rocks

  • were extracted.

  • Which is pretty amazing.

  • Of course, that still doesn't explain how people moved the rocks.

  • It seems like an overwhelming task, to the point where it's been proposed that the

  • rocks weren't moved by humans at all.

  • For once, though, I'm not talking about aliens.

  • I'm talking about glaciers.

  • It's been suggested multiple times that these huge stones may have been glacial dropstones,

  • carried by advancing glaciers and deposited when the ice receded.

  • But modern archaeologists tend not to agree with this.

  • For one thing, they point out that there's a lack of good evidence for glacial activity

  • on the Salisbury Plain.

  • We don't see any major piles of glacier-carried rocks, and certainly no deposits of the type

  • of stones used to build Stonehenge.

  • And for another, they argue you don't need glaciers to explain the movement of these

  • megaliths.

  • Again, human ingenuity is enough.

  • For example, some researchers think the rocks may have traveled over water.

  • Ancient peoples could have loaded them onto boats and carted them along rivers and coastlines.

  • .Some people have even traced out specific waterways that could have taken the bluestones

  • from the Preseli Hills in Wales all the way to Stonehenge

  • On the other hand, the stones could have also moved over land.

  • In 2016, a group of students from University College London conducted an experiment to

  • test just how hard it would be to move a megalith.

  • Inspired by technologies from ancient Japan, they constructed a large wooden sleigh laid

  • on top of a path of wooden logs.

  • They put roughly one-metric-ton of stone on the sleigh, and pulled it across London's

  • Gordon Square.

  • With only ten people pulling, they were able to move the rock up to three and a half kilometers

  • per hour.

  • So maybe Stonehenge architects used a similar technique.

  • Or, like other scientists have pointed out, maybe they just rounded up a bunch of people

  • and carried the rocks.

  • All in all, it's hard to say which of these ideasif anyis closest to the truth,

  • because no one has found any direct evidence of a transport route.

  • It has, after all, been an awful long time.

  • But there's good reason to suspect people were at least capable of moving these megaliths

  • without any help from magic or tractor beams.

  • Historians are still investigating why they might have gone through so much trouble, but

  • either way, with all of the hard work that went into building it, it's pretty clear

  • that Stonehenge was important.

  • It may have served a number of purposes, but scientists know for sure that it was a long-used

  • burial ground.

  • The cremated remains of more than 60 people have been extracted from beneath the monument,

  • and it's estimated that there may have been more than 150 burials at the site over its

  • centuries of use.

  • For a long time, we didn't know who these people were, but recent research ha s begun

  • to unravel that mystery, too.

  • New excavations at Stonehenge in 2008 opened up the doors for more modern scientific analyses

  • on these remains, including a technique called stable isotope analysis.

  • Unlike radiocarbon dating, this method looks at isotopes that haven't decayed much over

  • time.

  • And instead of being used to determine age, it can be used to examine the chemical makeup

  • of remains.

  • Kind of like the stones themselves, the bodies at Stonehenge hold the chemical signatures

  • of the environments they lived in, picked up from the water they drank and the locally-grown

  • food they ate.

  • That can tell scientists where they likely lived.

  • A 2018 study in Scientific Reports found that some of the bodies had isotopic signatures

  • that matched the local environment.

  • So these were probably people who lived nearby.

  • But others had signatures pointing to more distant regions like Devon or Wales.

  • Since these signatures are also affected by the type of wood used for the cremation process,

  • the .

  • It's not yet clear exactly who these people were, but it seems people from near and far

  • were buried here, maybe because their relatives were, or because this site was used by a culture

  • that was often on the move.

  • More digging and more research will hopefully tell.

  • Regardless, whoever it was that built, used, and buried their dead at Stonehenge, we do

  • know that they weren't alone.

  • Whether because of the environment or other factors, the Salisbury Plain is one of the

  • richest archaeological regions in the world.

  • There are hundreds of other burial sites and ancient remains, and researchers have used

  • all kinds of cool methods to investigate themincluding ground-penetrating radar and

  • lasers.

  • So there may still be a lot of mystery surrounding Stonehenge, but those questions aren't unanswerable.

  • And as we keep researching and introducing newer technologies, more scienceand more

  • knowledgeis yet to come.

  • Unlike the builders of Stonehenge, you probably won't be dragging megaliths across the countryside

  • any time soon.

  • But if you want to get in touch with your inner Bronze Age human, you can always try

  • pottery.b

  • Archaeologists have found plenty of pottery shards around Salisbury Plain, and thanks

  • to Skillshare, you can learn to make some of your own, too.

  • In this class, called Building Dishes by Hand, artist Emily Reinhardt teaches you how to

  • make ceramic dishes at home, without having to go out and buy a potter's wheel.

  • Which is pretty helpful, if you're just looking for something new to try out.

  • Also, there's just something really satisfying about storing your pins or loose change in

  • a little plate you made all by yourself.

  • Skillshare has classes on everything from design to public speaking.

  • And right now, Skillshare is offering SciShow viewers 2 months of unlimited access to their

  • over 20,000 classes for free!

  • To check it out, you can follow the link in the description.

  • { ♪OUTRO }

Thanks to Skillshare for supporting this episode of SciShow.

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What Science Has Taught Us About Stonehenge

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    joey joey に公開 2021 年 05 月 19 日
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