How We Learn About Ancient History Using Carbon | Carbon Dating Compilation

thanks to brilliant for supporting this episode of scishow go to brilliant.org scishow to learn how you can take your stem skills to the next level and save 20 on an annual premium subscription [Music] carbon dating is not the precursor to carbon marriage it's a way to figure out how old something like stonehenge is based on the carbon in it and some forms of carbon age more gracefully than others so by looking at where different objects are like well-arranged giant rocks in england in that carbon aging process researchers can figure out how old that thing is but it's a lot more complicated than that so it's a good thing michael's here to explain it if you want to know how many carbon atoms there are in your body write down an 8. next write down 26 zeros that is 80 trillion trillion but about 80 trillion of those 80 trillion trillion are super ultra carbon atoms an isotope of carbon known as carbon 14. these atoms are important because we can use them to figure out how old something is in a process known as radiocarbon dating as long as it's dead in less than 50 000 years old normally carbon has six protons plus six maybe seven neutrons but carbon 14 with eight neutrons can form high in the earth's atmosphere when high-powered cosmic rays start a reaction that ends up giving an extra neutron to an atom of nitrogen this neutron-infused nitrogen isn't stable so it quickly dumps a proton turning it into the more stable carbon-14 now all life on earth needs carbon but it isn't picky about what kind of carbon so organisms happily take up carbon-14 to make the compounds they need when plants turn carbon dioxide into glucose for example some of that co2 contains carbon-14 and eventually that carbon makes it all the way up the food chain which is why all living things have some carbon-14 in their molecules but that carbon doesn't stick around forever because it's not completely stable at some point it undergoes a process known as beta decay in which basically it loses an electron turns one of its neutrons into a proton and becomes nitrogen 14. and luckily for scientists who specialize in studying old biological material like archaeologists this decay process happens at a fixed rate we know that it takes about 5 700 years for half of any given sample of carbon 14 to decay into nitrogen 14. this time span is known as its half-life so after one half-life you'll have half of the c14 that you started with after two half-lives you'll have one quarter after three you'll have an eighth and so on this is useful for dating dead stuff because while living things are constantly taking in carbon about as fast as it decays inside them after death there's no new carbon coming in so when the c14 decays inside the dead organism the proportion decreases more importantly it decreases at the same rate no matter what the dead thing is so let's say you find an old piece of a dead tree since we know that about a trillionth of the carbon atoms living in the thing are carbon 14 all you have to do is measure how much c14 the dead thing has and do some calculations of course figuring out how much c14 a sample has turns out to be a little bit complicated the first scientist to try it was american chemist willard libby in the 1940s who used a geiger counter to measure how many beta particles a sample spat out over time he could then calculate the proportion of carbon 14 and figure out the age of the sample libya ended up winning the nobel prize in chemistry for figuring this out but since the late 1970s scientists have been using a better method called accelerator mass spectrometry or ams in this rather long and expensive process a sample is bombarded by ions shot through a particle accelerator and finally separated by magnets to isolate individual carbon atoms that can then be measured ams is a lot more accurate than the beta decay method but its range is only about 50 000 years because at that point there's so little c14 left that we can't reliably detect it so to date samples that are older than that like fossils scientists track other elements like uranium or potassium which have half-lives in the millions of years but there are still other problems it turns out that the amount of c14 in the atmosphere has changed occasionally over time several decades worth of nuclear bomb tests in the 20th century for example managed to create a big spike in the amount of c14 in the atmosphere but at the same time all the carbon being vaulted into our atmosphere by burning fossil fuels may actually be diluting concentrations of the izotope as a result scientists often have to combine radiocarbon dating with other methods like tree ring dating to corroborate their findings i mean you probably already know this but dating is hard especially when what you're dating is dead if in the end all we can rely on are death and taxes then it sure is great that we figured out how to turn that reliable carbon death into a useful tool but it might not be all that reliable after all it's in danger from some of the same phenomena that put us in danger here's why for researchers studying objects younger than 60 000 years or so carbon dating is one of the most valuable tools out there it involves analyzing the ratio of two kinds of carbon atoms and with it scientists have figured out the ages of everything from mummies to old manuscripts carbon dating has transformed fields like archaeology and paleontology and it's helped us get a much better understanding of what the world was like thousands of years ago the problem is carbon dating might also be in danger thanks to fossil fuels of all things the idea of carbon dating was first proposed in the 1940s and it was important enough to win its discoverer a nobel prize it relies on two kinds or isotopes of carbon one called carbon-12 and another called carbon-14 carbon-12 or c12 for short is basically normal carbon it has six protons and six neutrons and it's stable so it doesn't change in decay into different atoms over time carbon 14 is rarer and it does decay c14 has two extra neutrons which makes it unstable over about 5730 years half of the atoms in any sample will turn into a more stable form of nitrogen that's called its half-life carbon-14 is produced when radiation from objects like the sun interacts with those stable nitrogen molecules as they're floating around in earth's atmosphere then the c14 ends up in carbon dioxide and works its way into plants and animals through photosynthesis and the food chain historically speaking the amounts of c12 and c14 in the atmosphere have been roughly consistent over the years so scientists can expect to find a predictable ratio in most organic materials that ratio is what carbon dating is based on so say researchers were trying to figure out how old some frozen animal tissue is if their sample has less c14 than normal that suggests that it's been around long enough for that carbon to decay so it's older but if they have a sample where the ratio is normal it's probably relatively new by tracking exact ratio changes and knowing the half-life of c14 scientists can usually pin down an object's age to within a few decades carbon dating has worked for years but now there's a problem that consistent carbon ratio is changing admittedly it has changed before but those changes were small enough that they weren't a huge deal and the results could be easily calibrated with other measurements but now things are getting more dramatic over the years as we've burned fossil fuels we've launched a lot of extra carbon dioxide into the air and since those fossil fuels are so old almost all of their carbon 14 has decayed which means we're adding a bunch of carbon 12 to the atmosphere so much that it's really messing with the ratio that scientists use for carbon dating officially this is called the suez effect after the scientists who first noticed this pattern in the 1950s and it's not great news according to one 2015 paper if we keep burning fossil fuels at this rate we'll add so much extra c12 to the atmosphere that new materials in 2050 will seem a thousand years old there will be so much c12 in them that the amount of c14 will look tiny and decayed by comparison and without an outside reference it will be almost impossible to figure out how old they really are many groups are already working to reduce the rate at which we burn fossil fuels and that's good for everyone not just archaeologists but we probably won't stop using them completely anytime soon thankfully one researcher came up with a solution to help us sort through this mess or at least it's a reliable way to tell if fossil fuels have skewed measurements in a 2016 paper published in the journal environmental research letters he suggested we just look at a different isotope of carbon carbon 13 or c13 has just one extra neutron and like carbon 14 it forms naturally but it's pretty rare plants don't really store it so there isn't much of it in fossil fuels or current living things and it only makes up one percent of the earth's atmosphere so it's also getting overshadowed by all that extra c-12 we're putting out there but unlike carbon-14 c13 is stable that means the amount in a sample should be predictable and shouldn't change over time so researchers should see a constant percentage of c13 that is unless there's a skewed amount of carbon 12. in his 2016 paper this scientist suggested that researchers should always check on that c13 percentage during the carbon dating process if it's unusually low they'll know the sample is affected by extra carbon 12 so traditional carbon dating won't be reliable they'll have to use another method for example if an organic object was found in a hard rock layer researchers can estimate its age by dating the rock which doesn't always require carbon ideally we'll be able to stop this problem by reducing our fossil fuel usage but since that might not happen soon this carbon 13 strategy will definitely be helpful and wouldn't you know it it always comes back to climate change but at least we've come up with a way to know if carbon dating is reliable carbon dating is a technique that requires both scientific insight and a thorough grounding in math and brilliance courses in science math engineering and computer science can help you acquire those skills whether you're a professional or just a super curious person for example if you feel like math lessons in school never clicked for you then their new course everyday math might be perfect for you by revisiting topics ranging from fractions and number lines to geometric shapes and area you'll reinforce the foundations of your mathematical knowledge and sharpen your problem solving strategies and it's designed to be way more interactive than your dry math textbooks ever were all of brilliance courses include guided problems with explanations so you can see where the answer comes from and gain insight into the next one to get started head to brilliant.org scishow to save 20 on an annual premium subscription to brilliant and thanks to them for sponsoring us today now by using all of that math and science we can even carbon date stonehenge hank will explain look you don't have to know a lot about ancient history and prehistoric monuments to have heard of stonehenge the story of this incredible structure goes back more than 5 000 years and while it was certainly important to the people who built it those architects would have no way of knowing that their creation would become world famous these days stonehenge is featured everywhere from popular movies to your friends vacation photos but if there's one thing that everyone seems to know about stonehenge it's that there is 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 is buried beneath it and especially how did ancient people manage to move and erect these huge stones over the years lots of explanations have been proposed including lost technologies outright magic of course you've got aliens so 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 fascinating and 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 jeffrey of monmouth a bishop famous for his fanciful writings on british history in the 1100s he claimed that the monument was built by merlin yes the wizard merlin of the 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 myceneans 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 that 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 isotopes like 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 myceneans or merlin for that matter 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 day or even a century 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 hinge it's possible that some of the 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 who exactly did the heavy lifting here 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 of these rocks into place was no easy task there are two major categories of stone also called megaliths at stonehenge there are the enormous sarsons typically weighing around 22 metric tons each while the smaller blue stones are a modest two to five metric tons today there are around three dozen stones at the site arranged in two outer circles and two inner horseshoes but based on 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 lentils 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 very very heavy piece of ikea furniture admittedly this is some pretty advanced engineering for that time period but unlike what a lot of internet forums and youtube videos say it is not impossible the builders might have lived a few thousand years before cranes and power tools but they still had all that good old-fashioned human ingenuity and human muscle which we tend to overlook also never underestimate the power of a good rampant pulley system archaeologists think major work on stonehenge continued until around 1 500 bce and in that time more earthwork features were dug and the blue stones were rearranged multiple times but who built the structure and how aren't actually the biggest questions scientists and historians have asked instead the real mystery is how the stones got there see the big sarsons are made of sandstone and the blue stones are variously formed from rhyolite dolorite and other types of rocks 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 sarsons came from a region called marlborough downs around 32 kilometers from stonehenge and the blue stones most likely came from the priscelli 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 blue stones 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 these 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 drop stones 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 blue stones from the priscelli hills and whales all the way to stonehenge on the other hand the stones could also have 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 10 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 ideas if any is the 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 that people were at least capable of moving these megaliths without any help from magic or space 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 has begun to unravel that mystery too new excavations at stonehenge in 2008 opened up the doors for more modern scientific analysis 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 in the locally grown food that they ate that can tell scientists where they likely live 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 that pointed to more distant regions like devon or whales since these signatures are also affected by the type of wood used for the cremation process the researchers were also able to find evidence that some of the dead were cremated elsewhere and brought to stonehenge for burial it's not yet exactly clear 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 them including ground penetrating radar and lasers so there may still be a lot of mysteries surrounding stonehenge but those questions aren't unanswerable and as we keep researching and introducing newer technologies more science and more knowledge is yet to come so we often use carbon dating to uncover stories from the past but what about predicting the future with carbon earth's climate has been through a lot over the past few billion years and at this point scientists have a pretty good handle on how our planet has changed over time but we talk about the future of the climate too about how it's changing more quickly than it has in the past and about the dangers of rising temperatures and more severe droughts and storms our methods for predicting the future of climate are a little different than those for reconstructing the past the past leaves physical records we can study in things like tree rings and ice cores the future requires us to be a little more abstract so we mostly predict the future of earth's climate using computer models mathematical reconstructions of our atmosphere that account for as much detail as possible to produce an accurate simulation and it's taken decades to build them up to the point where we can be confident that what they say is accurate but it is and what the models say is that our climate is changing and humans are making it happen global climate models or gcms grew out of early computerized attempts to model the planet's atmosphere in the 40s and 50s scientists weren't even trying to predict the future they just wanted to create a representation of the earth's atmospheric system as it was at the time that was hard enough climate models then and now divide the earth's surface into chunks a few hundred kilometers on a side each with different properties like air movement and surface temperature then the computer calculates how all those chunks interact with each other to see how things change over time those early models were super simple they did things like combine land and sea into a single damp surface with no geography or represent the earth as a cylinder instead of a sphere because the poles confused the computer thankfully this didn't lead to a whole movement of cylinder earthers though all this simplifying was necessary because early supercomputers were kind of limited we're talking like five kilobytes of ram your phone has like 500 000 times that much still it was enough to come up with a crude picture of earth's atmospheric currents and its wet and dry regions eventually though scientists wanted more than just a model of the atmosphere around a featureless cylinder they wanted something that fit an actual planet now they could make the model more accurate by making the chunks smaller but that would take more computing power and what about the effects of mountains on air movement what about the warm and cold water circulating in the oceans to answer those questions climate modelers needed more juice by the 1970s they were also beginning to worry about the greenhouse effect of the carbon dioxide we were adding to the atmosphere using fossil fuels they thought it could trap the sun's heat and cause the planet to warm at the same time computers were getting powerful enough that they weren't limited to modeling the present anymore so programmers wanted to start using models to predict future changes in the climate but before a climate model can be turned loose to predict the future it has to be able to predict the past what's known as hind casting and that's an important test because if the model's predictions match what we know already happened we can be more confident about what it says will happen in the future temperature records go back a century or more if you start a model in 1850 it should be able to progress through time and match the general trends and temperature we already know happened and by the late 1970s climate models started to be able to do this in 1979 a report pulling from two different climate models suggested that the earth's temperature would increase as atmospheric carbon dioxide increased specifically assuming twice as much co2 in the atmosphere they predicted an increase between 1.5 and 4.5 degrees celsius which trends suggested could happen before the 21st century was up that range has proven pretty reliable ever since and it still fits the warming we expect to happen over the next century or so even as models have become much more powerful so models in the 70s were able to answer one simple what if question what happens if the amount of carbon dioxide in the atmosphere doubles but these days you can carry more computing power in your pocket than those early programmers ever dreamed of and used it to send people pictures of your cat that disappear after 10 seconds truly it's a golden age and not only are cat pictures better but so are climate models we now have the resources to ask and answer more detailed questions and boy do we have a lot of them governments want to know what will happen in detail in their corner of the world and scientists want to know what will happen if we take measures to stop global climate change as opposed to letting emissions run rampant with the models we have now we can produce more customized predictions based on different scenarios of what humans might do in the future like how much carbon dioxide will be emitted over a given amount of time and how much land will be used for agriculture you can also use these models to basically run the predictions backwards and calculate the factors that would lead to a certain amount of warming so for example if policymakers want to see what changes should be made to limit overall global warming to 2 degrees celsius they just have to use a climate model with the appropriate parameters that said just because it's the 21st century and computers are awesome now doesn't mean that climate models have reached their perfect final form the earth's atmosphere is an unbelievably complex system and we don't yet have models powerful enough to track absolutely everything we also can't account for every single thing humans do now or might do in the future so we now know a lot about what will happen but there's still work left to do in perfecting our predictions for example up until 2012 or so models weren't that great at predicting sea level rise they undershot it pretty badly un reports in 2001 and 2007 made predictions for sea level rise that failed to track with what we observed via satellites by about 60 percent that might be because the models didn't fully account for the rapid changes in the ice sheets over antarctica and greenland for the un's most recent report in 2013 the models were reprogrammed and the projections for sea level rise increase to be more in line with what we're seeing happen we want our models to do better in part because we want to know what's going to happen to our climate and in part because accounting for all the variables is just good science with these constant improvements every new prediction can be more detailed and in the last couple of decades we've started to be able to tailor predictions for specific regions which is helpful because people and governments in different parts of the world want to know very different things a farmer in southern europe might want to know if drought will affect their crops more severely in the future while an islander from the maldives might be more concerned about their country being completely swallowed by rising seas now we can try to answer those questions and a lot of the answers aren't encouraging no matter how you look at it the models are very clear that the planet is warming that's one of the easiest things to predict i mean we've been doing it since 1979. if we pump more heat trapping greenhouse gases like carbon dioxide into the atmosphere the numbers come out warmer there are factors other than greenhouse gases that the models take into account too like particulate matter from volcanoes and coal burning power plants which can have a cooling effect and we know the oceans will slow warming for a while by absorbing co2 until they run out of capacity but all the predictions say the warming caused by greenhouse gases will have a stronger effect even in scenarios where governments around the world work quickly to limit and phase out greenhouse gas emissions climate models predict that the earth's temperature increase will be at least around 2 degrees but in other scenarios where we take less aggressive action or no action at all the planet's average surface temperature goes up by more like 6 degrees celsius which if you're used to fahrenheit that's 11 degrees that's hot but higher temperatures are far from the only consequence of climate change using models along with other tools researchers predict all kinds of other effects a comprehensive report by the u.s global change research program published in 2014 lists some of the consequences it emphasizes effects on north america but similar things would happen all over the world with more and more time passing between periods of freezing temperatures plants could experience a longer growing season and that could actually have a net positive effect of causing plants to take up more co2 so less stays in the atmosphere but the good news pretty much ends there in general around the world and in north america there would be changes in the distribution of precipitation including rain and snow and the changes tend toward increasing extremes a warmer atmosphere holds more moisture so wet regions will get wetter but models show shifts in large scale movements of air that would exacerbate dryness too so for example the dry american southwest will get even drier and major events like droughts heat waves and powerful storms will get worse and more frequent the effects of climate change on atlantic hurricanes are hard to predict we don't know for sure whether it was responsible for the devastating 2017 hurricane season but we know that as the global temperature increases the temperature of the surface of the ocean does too and warm ocean water is hurricane fuel historically warmer years don't produce more hurricane landfalls so we may only see stronger storms not more of them but that's not a sure thing climate change will have other kinds of effects too like rising sea levels melting ice caps and changes in ocean currents but it would take a whole other episode to talk about them all which is exactly what we did a few years ago thanks to decades of work improving climate models we now have a very good idea of what's happening both globally and regionally and even though our models have gotten much more detailed over the years those predictions of increasing temperatures have stayed constant which is a good sign for the science of climate modeling but also may be a cause to be a little worried we've always known that the earth wasn't just a damp cylinder but as our ability to model the climate has improved over time we've learned a lot about how our planet works and what we're doing to it so computer models can predict the past and the future in terms of temperature trends and atmospheric carbon dioxide in the end carbon is just one element but it's useful in so many situations so who knows what the next carbon innovation will tell us [Music]

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Keywords: SciShow, science, carbon dating, carbon, radiometric dating, half life, dating, climate change, stonehenge, Stefan Chin, Hank Green, what is carbon dating, carbon dating science, How We Learn About Ancient History Using Carbon, Carbon Dating compilation, how to use carbon, the past through carbon, carbon dating SciShow, carbon dating explained, chemistry, history

Id: v7ulKFTopM4

Length: 30min 20sec (1820 seconds)

Published: Wed May 11 2022