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0:05
Today's lecture is going to look at archaeological site dating. This is the way that we archaeologists can figure out how old something is on a site and how old the archaeological site itself is too. So these are going to be the techniques that we use to date artifacts, features, and the stratigraphy, the very site layers of an archaeological site. Hopefully, this will help you answer: "How do they know that?" "How do they know how old it is?" The next time that you come across
0:37
something related to archaeology or if you bring this class up while you're chatting with folks, now you'll have the answers. To thank you for your patience in listening to an audio recording instead of me coming to class, you get three dog pictures. So, Blackthorn got to go to a pumpkin patch and an apple orchard and these are some pictures of him hanging out on the farm. There are three main ways that we can date archaeological sites. The first one we refer
1:23
to as relative dating. You can think of this as comparative dating. Basically, we're going to rely a lot on that Law of Superposition that we discussed before the midterm and we're going to look at this to best understand that something is older or younger than something else on the site,. but we're not going to get those tight dates that you often see in newspaper articles or in videos.
1:55
To get those kinds of dates, we're going to look at absolute dating. This is where we can get a tight specific date or date range using a variety of different techniques. This will allow us to determine that a site is from 40,000 years ago or that an artifact is 500 years old, things like that. Finally, we're going to discuss the concept of cross dating, which is something that we can use in both relative and absolute dating and the concept of a TPQ, which stands for terminus post
2:34
quem. But don't worry, we'll get there. Now, the main reason that it's so important to understand the different types of dating is so that we don't take objects at their face value. You see, certain media can mean certain things when we find it, especially when it comes to things like the written record. And so, if we don't understand the culture history that's going on, it can really throw off our interpretations. And to showcase that, there's an example here up on the slide.
3:12
So you'll see two archaeologists that are going through a site and they're basically saying, look, what did I tell you? The inscription says "Like a virgin." "So I want to make sure I understand this," the other one points out," right? "These ancients worship someone named Christ and you think this is where they buried their mother?" Here's where the confusion comes in. First, it is true that in Christianity, the Madonna, as you can see up in the top right, is indeed a reference
3:50
to the Virgin Mary. But Madonna is also a music artist and Like a Virgin, when it came out, was playing off of the fact that she took the name Madonna to be her stage name and that the Virgin Mary also was referred to as Madonna, but that she also had a whole song talking about Like a Virgin. Now, the comic itself requires cultural knowledge because if you don't know about the figure of the
4:30
Madonna in Christianity and if you're not as familiar with the recording artist Madonna, the joke itself isn't going to work. It relies on past knowledge. As such, that same past knowledge is what a lot of our archaeological interpretations rely on. And so, a good archaeologist would never have gotten this confused because they would have known the culture history. And they would have known that Jesus and his mother lived at a very different time than Madonna. and they would
5:12
have known that anything associated with the time period having to do with Madonna would not have had the same imagery and iconography that we might see things associated with the Virgin Mary. Hopefully, this is making a little more sense. All right, let's continue. The first concept that I would like you to know in archaeological dating is that of relative dating. You can see the definition here and as it's been throughout the semester. Key definitions that you should
5:41
know are highlighted in bold. So the definition of relative dating is the dating of a site, context, an artifact, its layers. They're an examination of its place relative to or compared to other layers, contexts, or artifacts. This allows us to establish some sort of idea by creating a chronological relationship as in something is younger than something else. It is relative and that's where the name relative dating comes from. So we can use this law of superposition to develop
6:25
a timeline. If you look at the image here, you'll see that following the law of superposition, the youngest artifacts are up at the top. The oldest artifacts are down at the bottom. And so if you were to look at it, you would know due to an understanding of the law of superposition that the aluminum can and the plastic comb were inherently younger relative to the stone arrow point, the basket fragment, the bone all, and the pottery
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fragments that we see down toward the bottom. This relative dating works in the middle as well. If you look at the layer labeled stratum B, you'll see the glass bottle, horseshoe, and steel all are all the same layer, which means they're all going to be older relative to the layer above them, the can, license plate, and comb. And they're all going to be younger relative to everything below
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them. The shell button and the bullet in stratum C, the layer of sand and gravel in stratum D, and all of the oldest artifacts on the site in stratum E. You've already become acquainted with relative dating in a way because you had a very similar question when you were tested on the law of superposition on the previous exam. When you were asked to figure out what was older and what was younger based on two different objects, you knew that the older object was going to
8:15
be the one toward the bottom and the younger object was going to be the one toward the top. and that their age was relative. You didn't know how old they were. You just knew that the things at the bottom were older relative to the things at the top, courtesy of the law of superposition. So, in a way, you've already got relative dating down. Now, just to help you further understand, there's a concept that we archaeologists use to help us when we're doing relative dating.
8:52
Sometimes we come across a lot of different artifacts and we're trying to figure out where they go in terms of establishing this chronology because humans can hang on to old stuff and sometimes this change over time can be gradual. So we practice a concept known as artifact seriation defined here on the screen which is the chronological ordering of artifacts of a particular type or class. So in this case up on the screen you
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see cars and it's this ordering by style feature or design so that we can see changes over time. We used to call this sequence stating because we were forming a sequence of objects, but we now call it seriation because we're literally forming a tight series based on certain changes. So, it just works a little bit more easily. Now, you yourself can absolutely play along right now. If you look at these Cadillacs from 1 to six, take a moment and see if you can ascertain which one is
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the oldest and which one is the youngest based entirely on what you know of physical changes. In this particular case, it's not that the two at the top or the two at the bottom are inherently older or younger. They're not put in a stratigraphic order. But if you can see those changes over time, it should become apparent. You figured it out. Hopefully, you're writing it along in your notebook.
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The Cadillac labeled number one is definitely the oldest. It's a Cadillac dating to 1950 and the series for this artifact seriation progresses every 10 years. So a 1960 Cadillac is number two and then 1970. And there's some pretty noticeable changes between 1950 and 1960 and between 1960 and 1970. The shift, however, between 1970 and 1980 as personified by three and four. They're there, but they're starting to get less noticeable.
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The difference between 1980 and 1990 seen by four and five, it's enough for us to say that's definitely not a modern car. But the differences are still less noticeable than the change between 1950 and 1960, i.e. images 1 and two. And then there is a bigger shift between 1990 and 2000 which is images five and six where we see the greatest change is between images 1 and six or two and six. And that's because they have the greatest amount of time between them as well.
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Cars are an artifact that change very quickly over time. And so every decade will show us quite a lot of changes in features. Other things when we look at details, it might take a couple of hundred years before we really see a noticeable change in the shape of a certain type of ceramic or a certain type of spearhead. But we can still do the same thing by just looking at the image and all of its details. By looking at every aspect of an artifact, we can start
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to understand older ones look like this. Younger ones look like this. And if it's got some of the features of the young ones, some of the features of the old ones, it might be something that's kind of right in the middle in terms of age. So hopefully that's making sense. We can also use a concept known as frequency seriation. Now, it looks like a lot of scary math over on the side, but I promise it's really not that big of a deal. So, frequency seriation, the best definition,
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is one that really comes from your textbook. It's where this technique employs a percentage of artifacts and all of the little details that make them up to develop larger cultural sequences. So, put differently, it's a technique that allows us to create different series in chronological order by putting different descriptions of artifacts and all of the stuff within them into larger orders. What does this mean? What this really means is that we can look and we can say,
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"Hey, people hang on to old stuff. If something works, you're not necessarily going to get rid of it right away." Not everybody in 1990 got rid of their car from the 1980s. Heck, it is now 2025 and my pickup truck is over 20 years old and I'm still driving it because it works fine. So even though there are changes in things that we see over time, the reason we create this frequency seriation is
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to see when are most people changing to the new thing or when is this object used by most people? So when do we see the most of this type of object through time? And this will actually let us know how long people hang on to stuff. And this can be incredibly helpful because some stuff like a car you might hang on to a lot longer even if newer models come out than something like an iPhone.
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And an iPhone you might hang on to a lot longer even if newer styles come out than a pair of shoes or a certain type of pen or pencil. There are other things that even if new styles come along, you may have your favorite and so they'll continue to be useful even if the style hasn't changed very much. There are certain shapes for bottles out there that really haven't changed since the 1700s because they work. And if they work, we keep making them. So by looking at how people
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use their stuff and how quickly populations adopt changes in that stuff, we can better understand how to best date a site. The next term that I'd like to discuss is cross dating. You've already seen this term come up a little bit so far in the slides, but now we're going to define it. So cross dating is the dating of a site or context or even other artifacts in relation to something that we already have a fixed point on. We refer to this as an object of known age
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because as we've discussed before, archaeologists are bad at naming. So this object of known age, as you can probably figure out, is an object that we know the age of. And so we use this on a site to help us figure out how old other things are. And so in a way it's kind of a form of absolute dating because we do know the date of something and it can help us tighten things. And it's kind of a form of relative dating because sometimes all we know is that
17:23
something is going to be older or younger than the date associated with the object of known age. But the really nice thing is that if we find this object of known age, even if that particular object is pretty far away from where it was originally made, it can help us if we find it on the site. So, for example, if at the very bottom of a site, we have a type of ceramic and we know that that ceramic was only made in the 1500s. and that's all the way at the bottom of the site. We
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know that everything on top of the layer that has that ceramic has to be younger than the 1500s. And then if that's at the bottom of the site, the whole site itself can only date to the 1500s or earlier. And so that's a benefit of cross dating. If we have something smack dab in the middle of a site and it dates to 2,000 years ago, then we know that all the layers underneath it are going to be
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older than 2,000 years ago. And everything above it can be anywhere younger than 2,000 years ago. The other term I want to go over, and I apologize if you can hear theologist in training in the background. He wants to make sure that you're learning archaeology very well. And he's very into archaeological dating. The next term that I want you to know about is TPQ. Now, this stands for terminus post quem. It's kind of a mouthful, so we abbreviate it to TPQ. Now terminus
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post quem is Latin and it literally stands for point or end point after which we define it as the date after which there's that post quem a layer and all the stuff in it had to have been deposited and this TPQ becomes really really helpful when we're trying to average out just how old a certain layer is based on all the crap inside because rarely do we get things in an archaeological layer that are all dating to the same year. It would be nice if we had a layer and everything in
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it came from 1992. That would be awesome and that never happens. It would be fantastic and it would make dating so wonderful. But usually what happens is we have a layer and it'll have something from 50 BCE and something from 40 BCE and something from 20 BCE. And we have to figure out how old the dirt is based on this wide range of crap because now we've got a 30-year range of stuff inside one
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layer of dirt. So do we say that the dirt dates to the old thing that 50 BC or do we say it dates to the younger thing that 20 BCE? Well, this is where Terminus post quem can help us because what it tells us as a concept is that humans have always loved hanging under crab. We were just talking about this when we were talking about frequency seriation about how we need to look at how often people are using things the most, right? That people can hold on to old things, but that
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eventually there's a change where people start to pick up and use something new and we can see that change in the stuff they use, right? Right. So, Terminus post quem helps us with this too because it says people can hold on to old crap. But what you can't do, what you can't do at all is go in a time machine forward in time into the future, grab something from the future, and then travel back
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in time and drop it off. And because of this, we always have to date a layer to the date of whatever the youngest thing in that layer is. No matter how old the oldest thing in that layer is, because of our very tendency to hold on to old things. So, I'll repeat it again just in case.
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The TPQ of a layer is always related to the youngest, newest thing in that layer because humans can hold on to very old things. We're walking the earth right now with old things. If someone were to go into the Met and look around, for example, they would see lots of old things that were not made in the year 2025. And they could take a picture of them with very, very modern cell phones. And if something were to happen and the Met were to suddenly
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collapse and turn into an archaeological site, those super modern cell phones would be right next to those really, really old objects at the Met. But you and I both know that no one was taking a modern cell phone back to ancient Egypt. And so as archaeologists years later, what we would do is we would say, "Oh, there was some really old stuff that someone with a cell phone from the 2020s was looking at when the building collapsed. If you look on the screen,
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you can see some examples to try and help you test out this concept. So, if we look at the bottles on the left, we've got a bottle from the 17th century. That's the 1600s. And on the right, there's a bottle from the 18th century. So, that's the 1700s. If we find them in the same layer, ask yourself using the concept of TPQ, which one do you think would help us date the site? And following up on that, which date is the date of the site or at least the date of that
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layer? Is it going to be the 17th century or the 18th century bottle? Remember, they're side by side in the same layer of dirt. And we're trying to use TPQ to date that layer of dirt.
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Take a sec. Hopefully, you wrote down that the layer should date to the 18th century or younger because the 17th century bottle was held on to. But in the 17th century, that 18th century bottle didn't even exist yet. In the 18th century, both bottles existed. And the dirt has to date to a time period where both bottles exist. There needs to be a world in which both objects can exist.
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So, using the example from the Met again, if we were to find a layer that looked like it was a ruined museum and we were to have something dating all the way back 20,000 years ago and something dating to 2002 next to each other, would the layer date to the older date or the younger date?
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And again, hopefully you jotted it down that the whole layer, no matter how old that old object or any other object is, would date to 2002. So hopefully this is making sense. The example over on the right is also one that we can use because sometimes we don't have a whole century that we devote to dating something like the bottles. Sometimes we can have tighter information. We can get this from manufacturing records and from distribution records, shipping records. And that's
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the case with these ceramics. So the English salt glaze stoneware that you see, we know that this was in use by humans from about 1685 to 1785. And the cream wear that you see on the far right was in use from about 1760 to 1820. So if we're sitting here and we're trying to figure out what is the age range that these could possibly be. When we look at them, we realize that well, the TPQ for this site must be 1820 or later. Why? Because in the 1820s, we still have creamware and
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someone could have been holding on to English salt glazed stone wear. And you might say, but there's this period where the time periods are overlapping. And this is true, and it can make things somewhat confusing. But without any further information about certain types of patterns or anything like that, what we have to look at is just the fact that one is a lot older than the other. And so we have to say that in the 1820s, creamware was still being used. And so we go
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with the whole layer dating to the 1820s and the dates to the English salt glazed stone wear are somewhat irrelevant as long as we know that they came earlier. So hopefully this is making sense. Another way that we can do cross dating using an object of known age is by doing matching where we can take an object whose age we do know and use it to help us figure out where in time certain soil
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layers the artifacts are on a completely different site and this can in turn help us lock down that age of that site. So, for example, if we find a coin on one site and we get a nice clear date for that, this can help us establish a chronology. If there's a ceramic that is in a layer, let's say right underneath that coin, we know it's older. Has to be, right? The law of superposition, relative dating. So, it has to be older than the date of the coin. On the slide, you'll see one
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dating to 44 BCE. But the important thing is if beforehand we only knew that that ceramic was old, but we didn't really know how old. We just knew that it was older than other stuff because we found it kind of toward the bottom of certain site layers with other things piled up on top. Now we have a point in time. We know that it is older than 44 B.CE. And this is crucial because it lets us know that everything stacked on top of it is younger than 44 BCE. All because of the
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coin that we found on one site and could plug in to another site. And we can start using the law of association too where if we keep finding this coin with certain objects in that layer then we can realize hey around 44 BCE or later they're using this kind of ceramic. If we keep seeing that kind of ceramic in the layer above the old ceramic now we're really starting to lock it in. we can say this is a ceramic from around 44 BCE and this is an older ceramic and now we can start
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to really plug in a time for it instead of just saying well that's old that's young. So hopefully this is making some sense as to how cross dating can help us too and why we as archaeologists get so dang excited when we can figure out the age for something. All right, absolute dating. The thing that really gets us archaeologists excited. So, absolute dating is a method or a collection
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of methods that help us find a specific date or a date range for a layer, an entire site, a context or a specific artifact within it depending on how we're doing our dating. And in this regard, this is how we can sometimes come up with those objects of known age. So the most common forms that we use are dendrochronology, radiometric dating, and the written record. So if I were to ask you on an exam, is the written record a form of absolute dating? You would reply, absolutely.
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The important thing to bear in mind here is that there are dating techniques that you may learn in your other classes that go far beyond this. These are just some of the basics that I would like you to know. Dendrochronology is the first one that we're going to look at. So, dendrochronology can be broken down and remembered if you break down the word itself. Chronology comes from time, right? Kronos meaning time. So, chronology time or related to time and dendro meaning tree. So,
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literally tree time. So dendrochronology is where we date something using trees, specifically tree rings. And in this regard, it's actually a form of cross dating because we're able to take something of known age and extrapolate that data to help us lock in a date. So to do dendrochronology, we take samples of wood wherever we can find them at a site and then we match them up to known tree
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ring data. And these samples themselves are going to overlap and this will help us lock in the date. Now, this only works, as you might be thinking, on sites where we have wood. But we do have wood on more recent sites, on buildings that are still standing, on those sites of extreme preservation. So, shipwrecks and incredibly aid sites and frozen sites, right? The sites of extreme cold. And so
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where we do have access to wood, we're able to perform dendrochronology. Tree ring samples are collected all over the world. But there is a lack of data in certain parts of the world more than in others. Certain tree rings have been studied a lot more than others. And initially there was a belief that not all trees recorded their data the same way. And while that's kind of true, it was also a misconception for a while. And so there are literally less tree ring samples in some
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parts of the world such as South America. Which means if this is something that interests you, get out there and help us get tree ring samples. So, we look at cross-sections to best understand what's going on. And if you're trying to figure out, well, okay, that's great, but it's just a series of lines. What does that tell us? What we do is we best understand the life of the tree. And there's so much information packed into that that we can use. And so when
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we're done doing dendrochronology, not only do we get an idea of age, but we also get an idea of environmental condition. You see, trees reflect the lives they've lived in terms of the water they did or did not have access to. They lay down a new ring every single year of their lives. They lay down big, thick, juicy rings when they get all the water that they could need. And when things are tight and lean and drought filled, they still grow, but they lay down very thin
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annual rings. The thinner the ring, the drier the conditions. Trees that live overall in dry conditions will have thinner rings than trees that live in wetter climates. Where it really becomes noticeable though is when we see a pattern change. So when we see thin rings all of a sudden expand out, we know that there must have been unprecedented amounts of water. And when we see rings constrict and tighten, we know that there must have been a drought. The most recent year
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of growth, as shown on the screen, will always be the outermost ring of a tree. That layer just beneath the bark. And the very first here is going to be right at center, the ring that is around the heartwood or the very center of the tree. So, the very first layer that it put out during its first year of life. And it's usually pretty small and pretty narrow because if you think of saplings,
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they tend to be pretty small and pretty narrow. So we look at these samples and we try our best to match them up so that we can look for patterns that are the same. So the sample that you see on the left, you'll see that we have one sample that starts since 1798 and goes onward. Another one starts in 1871 and another in 1924. These were the years that the trees were planted, that they were finally able to lay down that first layer. But when we look, we can start to see things that
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line up. So, we start to see a thick band marking 1871. And we can see, all right, that's what 1871, 1872, 1873 looks like, both on the older tree from 1798 and the one that was born in 1871. Because if you look, you'll see it's got a series of two narrow bands. It's got a slightly wider band and then a really broad one in the middle. And that helps us line it up almost like a barcode. Again,
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we can find the same patterns that mark where 1924 is on that middle-aged tree. And we could keep doing it. We could find where 2013 is and onward and onward. And so this can help us when we take what we have and the sample of wood that we have and we match it up to see where its lines line up perfectly. and we'll eventually find that when we sample, we're usually not cutting down trees
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to get the sample, especially if we don't have a lot of wood on the site to begin with. Instead, we're going to very carefully take a portion of the wood. We do this by coring. And coring is also how we can get our tree ring samples. So, we don't have to cut down living trees either. So, for example, Choco Canyon, you see the wood here in this desert environment sticking out from the mud brick. And these wooden beams can help us figure out when the trees were cut down to be used
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to build the building. So, we drill a core. You basically drill a little tube like piece out of the beam. And then we take that tube of wood and we compare it to known information. And if we've got access to other trees nearby, a dead tree and a living tree near the site, we'll likely core those two and see if they line up. And if they do, we can take all of that information to better understand when the tree that was dead and the living tree date to to better understand
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the environment nearby. But we'll take all of this and we'll match it up with known tree ring databases that exist all around the world so that we can figure out what's going on. Now, generally, you're going to look for the tree ring database for the region that you're digging in because that's the one that's going to talk about the climate that your tree experienced. This doesn't work with shipwrecks because there we're going to see if we can find wood that matches it
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up. And if we can find something that matches those rings and layers, that'll actually tell us where that wood originally came from. It'll let us know, oh, these trees were cut down in Ireland or they were cut down in New England, and we can match it that way, thus letting us know perhaps what shipyard the ship originally came from. This can be incredibly helpful if we're trying to identify a shipwreck who maybe has lost its name to time. Here's an example of two broad tree rings
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in the way that they can give us information about their history, about their environment. and the way that two similar time periods can look very different in different parts of the continent. So on the left hand side there's a Douglas fur from the American Southwest. It was planted 1527 and the tree rings here extend up past 1650. The important thing to bear in mind is that if you look at the period between 1550 and 1600, that's 50 years,
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you'll see that that area is much much smaller than the area between 1600 and 1650, which is much broader. It almost looks blurred, and it's not a photo resolution problem. Instead, it's showing what's referred to as the mega drought that took place in the region starting roughly around the 1560s and continuing all the way to the 1590s. And in this case, the rings look like they're blurred. You can barely see them. In contrast, you can see this bald cypress from Virginia. This is
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a much wetter climate. We see it's planted around 1531 and its tree rings extend out past the 16s. But what's noticeable here too is that while the tree rings are broader overall, we start to see a contraction a little bit before 1600 and then we see a really tight contraction in the 16s and just before. Why does this matter? This tells us about two significant droughts. One happening in
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the late 1580s and one happening after the year 1600. And we can count them. You can sit there, get up close to the screen and literally count after the year 1600 what happens. And this coincides with events that we know about in history. There is a drought that was recorded in 1587 that corresponds with the settlement at Rowan Oak and the hardship and subsequent disappearance of it. It's often been referred to as the lost colony because it wasn't until recently that
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we knew what happened to its inhabitants. Similarly, that tight band from606 to 1612 coincides with the Jamestown drought where we know that the population, the settlement of Jamestown suffered greatly and there was a famine and there was a drought. And as a result, not only did the population become decimated, but a few of the inhabitants of Jamestown even turn to cannibalism.
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