 How can you tell which direction these iron particles are pointing when you're in the field? Well, in the field right now there's no, in the field of archaeology, there's no way to measure these directions in the field. You have to take some of these samples and move and take them back to the lab. And since it's a direction that is most important here, you have to collect the samples for their transport back to the lab in an oriented fashion. And that's where the field technique of archaeomagnetism comes in. That's where the elaborate process of cutting out the pedestals and pouring the plaster, scraping them off, marking them, measuring them with a brunton compass, where all that comes in. It's simply an attempt to take a piece of this oriented material before it's had a chance to move its direction back to the lab in a controlled fashion. We want to control for both the horizontal direction and the vertical direction, so you level it. After the students get through collecting the samples in the field, they're oriented in these plaster cubes according to horizontal direction and vertical direction. If you'll hand me that. You can see inside here, this one wasn't quite filled, but this is a piece of the material that is encased in this plaster cube. And then ideally you would have one that didn't have any holes in it. And this is how the material is preserved. And this is what we'll do the measurement in the lab. All right. Now these markings, you have to have marked north on the cube. Is that right? Right. It doesn't matter. The convention we're using here is we just mark the corner from which the direction was taken. We measured from this corner to this corner. And in the field notes there will be recorded the magnetic direction of this side of the cube. And the other markings on the cube simply are identification to keep that cube from getting mixed up with other cubes. It wouldn't make a problem. We use a magnetic needle or magnetic compass to control for the horizontal direction. That is, we measure this side. But it's important to remember that we're also controlling for the dip of it. Depths of the magnetic field? No, no. The dip of the magnetic field. How not only has it changed in horizontal movement, it's also changed from what you can think of as vertical movement up and down. Most people don't realize that. But we have to control for that. We don't simply measure what the surface or the top is in terms of its dip. We level it. And you've seen out in the field putting on the cross test level and leveling the top of the mold. Now, the reason this is important is simply to know how this was oriented in the field. We know that every one of our cubes was perfectly level. It had no dip. So that any dip we measure in the sample itself comes from the ancient pole position, not from the fact that the cube was straight. What other methods do you have to date these materials? I'm primarily interested just in archaeomagnetism, but archaeologists have available to them a number of other techniques. In the Southwest, primarily dendrochronology, the accuracy of which you can't match. And also C14 dating, which is created almost in a revolution in the rest of North American archaeology, and its ability to provide temporal control. Then you have archaeomagnetism. I think right now that those would be the three major absolute dating techniques. What is dendrochronology? Yes. Dendrochronology is also termed tree ring dating. Simply counting the number of tree rings that you have on a roof beam in a preserved Pueblo, let's say, and matching those rings, the sequence of those rings, to a master chart that's been developed primarily through work in Tucson, Arizona at the laboratory of tree ring research. And you mentioned C14. What test is that? Radiocarbon dating or C14 dating is fairly complex, at least as complex as archaeomagnetism, but basically what you're counting or measuring is the rate of decay in radioactive carbon. And it occurs at a fairly constant rate. And so by measuring the stable to the unstable radiocarbon atoms present today, you can calculate back about how old something is. Let me ask you, must you always have a charge sample to perform any of these tests? You mean any of the other dating techniques? Yes. No, tree ring dating actually would be better with a log that hadn't been burned. You can do it with charred roof beams, but it's a little clearer if it hasn't been burned. With C14, of course, it carbonized material. That's all you need. Usually it doesn't preserve in archaeological sites, but when it's burned, it is preserved. And that's why you end up usually using some burned organic material. And of course you need a burning for archaeomagnetism, but you're not dating the material that was burned, the wood in the fires, you're simply dating the material that got cooked underneath it. And how old are these techniques? Are these techniques very old? Not too old by comparison to archaeological material. They are in a constant process of developing, but by and large we have all these techniques been developed in the last 50 years. Dendrochronology, I believe, was developing in the 20s and maybe 30s. C14 was developed in the 50s, and it's only been in the last 20 years that you had any work at all done with archaeomagnetism. And I feel like that there's a real opportunity here within the last two or three years for a tremendous increase in archaeomagnetic dating technique. Once we've collected these oriented samples in the field and we bring them back to the lab and measure them in a laboratory magnetized. Once we've collected samples in the field, oriented samples, we bring them back to the lab for measurement. And we measure them on these laboratory magnetomers that are a little different from the magnetomers that you were used in the field at the archaeological sites. Those magnetomers were for locating soil anomalies, particularly features that might be buried underneath the ground that would be of interest to the archaeologists. This magnetometer is much more sensitive and is used for directional information. It will help you determine not only the intensity or differences in intensity between samples, but also the direction that the samples are actually pointing. Yeah, go ahead. Alright, turn it on. Rolling. Alright, now we're going to change the cue orientation and remeasure it so that we can average out any sort of irregularities in the magnetism of the clay specimen. Archaeomagnetism illustrates something that's very common in archaeology, that is the, or in science generally, that is the cooperation between disciplines. Archaeomagnetism developed out of geophysics and it was applied in archaeology, but at the same time the geophysicists were dependent on archaeological dating control to establish the first master records of how the Earth's poles were moving. And this sort of cooperation continues today. Archaeomagnetism is a dating technique. It was originally developed in geology in a technique called paleomagnetism where they're interested in changes in the Earth's magnetic field. And there were very, very major changes, particularly reversals in the polarity of the Earth's field. The north pole was the south pole and the south pole was the north pole. These geophysicists who were interested in paleomagnetism became interested in archaeomagnetism, that is using archaeological material in studying these changes in the Earth's magnetic field. And this is where the word archaeomagnetism comes. It's an attempt to distinguish it from paleomagnetic work. Paleomagnetism deals with rock cores and going out and doing geology, basically. Archaeomagnetism goes out to an archaeological site, collects archaeological samples, burned hearths or floors, what have you. The technique for collecting is quite different. You've seen pictures of how that's done. In paleomagnetism they're essentially coring with a drill and taking the rock samples back to the lab. Well, what use is this to an archaeologist? Magnetism is of use, as any dating technique would be used. I think, and I have a little bit of a bias here because of my interest in dating, but the public's interest in archaeology is primarily one of how old something is. This is one of the primary pieces of information that the public has a right to expect from an archaeologist. Well, archaeomagnetism is just contributing to that body of information. How old sites are? When were people living? What were they doing? When? And how long did it take for certain changes to occur? And you can tell when the last fire was in a fire pit. That's the essential event that archaeomagnetism dates. Other techniques date other aspects of life at a site. But archaeomagnetism tends to date the last activity at a site, either the last burning of the room. If that coincides with when they left, it probably wasn't much use of the room after it was burned, but they could have left a long time before it was actually burned. Some vandals came back later and torched the place. And then you'd actually be dating the torching of the site. What archaeomagnetism dates is the last uses of sites, of activity areas, and that sort of thing. Well, I don't understand the theory behind it. How do you go about figuring out the dating? Well, there really are two things you have to understand in the technique of archaeomagnetic dating. One is the theory behind why there is changes in the Earth's magnetic field. And the other is why archaeological sites record this change. And I think it's best just to deal with one and then the other. The first problem of why there is change in the Earth's magnetic field is a problem that was the original reason for development of the technique. Geophysicists were interested in why the Earth's field changes. Why is there what they call secular variation? And it has to do with theories about the core, and they're still arguing about these theories. And so there isn't a real answer to that question, why the Earth's magnetic field changes. But what's important to archaeology is that it does. The problem for archaeology, given the fact that the Earth's magnetic field changes, is knowing when this field was at certain places when. That is, recording the actual movement. So geophysicists began to use archaeology, and they did it in the southwest where they had good dating control already with dendrochronology primarily, tree ring dating. They would go to a pueblo or a room that was dated by tree rings. They'd know fairly closely when the room was occupied. They would collect an archaeomagnetic sample out of a burned feature there and determine what direction it was. So they would have a direction pointing someplace on the globe, and if we could sort of try to imagine the northern hemisphere up here. And we're down here somewhere in the southwest part of the United States. You have a pueblo room that you know when it was built, and you've made an archaeomagnetic collection here. And it points to someplace on the globe, and you can date that fairly closely. It was 1,300 plus or minus 50 years. And then you go over here to another site in the southwest, and you notice that it's pointing over here. The collection is pointing there. And it dates, the room dates to 1,350 according to tree ring material. Then you have another site that dates 1,400 according to tree ring dating, and this is where the archaeomagnetic sample points to. So you can begin with hundreds of these points to construct a curve of how the Earth's magnetic field has changed, how the declination and inclination of the local field has changed. And as a matter of fact, this curve gets very, very complex, and it wanders around and wanders around and wanders around and crosses over itself a number of places. Why does it change? Well, again, this is the question that was of interest to the geologists, the geophysicists, and it involves the nature of the Earth's core. And as far as I understand it, there's no answer to that question. There's theories, and there's conflict there about deciding which one of these. And it's hopeful. Geophysicists are hopeful that the archaeological evidence provided by this secular variation curve will help them determine the nature of the Earth's core and the cause of magnetism and why does it change? Why is there change in the Earth's field? But right now, I don't think there's a real good, clear answer to that. Well, do you know how fast it moves? For instance, one degree every ten years, or what? That's precisely how fast it does move. On the average, one degree, the rate of movement is not constant through all this time period, as it turns out. Sometimes it's moving faster than other times. But on the average, given the entire time range, the Earth's field moves about one degree every ten years. So you can figure that in ten years, your compass will not be pointing quite to the same place. It'll be about a degree different than it is right now. Does that mean from the samples that they've gathered at the archaeological digs, you can tell within a ten-year period when they abandoned the site, for instance? Not precisely, because there is some inaccuracy in measuring this direction. If you knew precisely where the hearth was pointing, you're right. You would know something about probably a ten plus or minus ten-year act. But there's inaccuracy in dating the original curve, how the pole has moved, and there's inaccuracy in measuring the actual direction that the hearth is pointing. So all those inaccuracies combine, and in collecting the hearth, all these inaccuracies give you an archaeological date, which is generally accurate to about 30 years, plus or minus 30 years, which is not too shabby, given a lot of archaeological evidence. Let me get this straight. Why is it so important that a piece has to be charred or burned? This is one of the most important aspects of the archaeomagnetic technique. Exactly why you can measure this direction. Why in these sites there's a recorded ancient polar position? And the answer to this question involves the nature, the mineralogy of clay. And in clay, just ordinary clay that you'll find in almost any site, there will be very small microscopic iron particles. You can sort of imagine them being randomly placed in this clay. Just sort of any direction. Now, the interesting thing that happens is that when this clay is heated up to very high temperatures, about 600 degrees centigrade, in fact, it doesn't even have to get that hot, these iron particles, very, very small, begin to align with the current field. The current field begins to determine their alignment. They become very, very agitated in this hot state. And as it cools down, they are locked in certain positions. And those certain positions are the field at that time. And they remain in that alignment. So before heating you have it, random after heating you have it in this sort of parallel alignment. This is idealized. And they're all pointing north, for instance, or magnetic north? Magnetic north at that time. And it doesn't change. It's a very important feature. It's preserved. If it's reheated, say it was reheated 50 years later, everything would become re-aligned to the Earth's field at that time. But if it was never heated again, then that's the direction that you would get. You tend to get the last firing of a feature. If it's a fireheart, it'd be the last time it was used for cooking or heating or whatever. If it's the burning of a room, you would get the burning of that room, the direction of the magnetic field at the time that firing occurred. Now... Well, when they take it from the hearths and bring it to the lab, how can you tell which direction the sample was pointing? That's an important question because really what you're after is this direction. This is what you want to know. But right now there aren't any instruments. There's no technology for going out to the field and setting up a machine over the hearths and saying, Hocus Pocus, what direction are you going? Hi, Roland Barrett at the Morgan Ranch in Areola. This was settled way back in the early days by Mr. Morgan, Mr. H. Frank Morgan. And I know that Mr. Morgan is one of the first men that had the idea of promoting the Glorys River Project. In about the years of 1912 or 1914, he spent $3,000 of his own money just to find out where the water would go, just the high line. But he could get no support, so I know that from then on, every chance he had, he boosted for the project. But he couldn't afford to spend any more of his money and money was hard to get those days. The southwest corner of Mr. Morgan's land and he had the post office up there where those buildings are. But all this ground where these buildings are here was in orchard and is a beautiful orchard to find varieties and he hauled water from the Glorys River in barrels to set that orchard out when he came to this country. I made a living here for five years and then the man that owned the farm was superintendent of the sugar factory in Rocky Ford, his name was Noble, and he wanted to sell the farm and we couldn't get together. So I had a chance to get a farm over here across the draw and I moved over there and lived over there for five years. And while I lived here, the log cabin burned down and I built another house here. I'll show you how it's been moved. This man moved it when he built this fine house here. But I'll show you the house that I built and lived in while I lived on this farm. Did you make a... And that was here and I raised spuds but I had some experiences of spuds. That's when the war was going on and they said plant beans and spuds feed the soldiers. I planted beans in the orchard here and I plowed up some good pastures, raised spuds. The next year the war was over, I hauled the spuds out and...