Stratigraphy -- Reading Earth's HistoryThis preview shows page 7 - 10 out of 10 pages. Subscribe to view the full document. I cannot even describe how much Course Hero helped me this summer. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero. University of Michigan, Dearborn. ANTH Anthropology Exam 1 Study Guide Part 1.
University of Michigan, Dearborn. ANTH Anthropology Exam 1 Study Guide Part 1.
B ancient environments using samples of ancient. Uploaded By Fasinais. Systematic survey and excavation. Informed consent refers to people's agreement to take part in research after they have been fully informed about its purpose, nature, funding, procedures, and potential impact on them. Anthropologists who study the past do not have to worry so much about ethical concerns, since their studies do not concern living people.
The most reliable evidence to study the past is that which is visible to the naked eye. Anything microscopic is too small to be considered reliable.
Archaeological anthropologists excavate sites to gain a better understanding of the regional patterning of the molecular record. Digging according to arbitrary levels is quicker but less refined than digging according to the site's stratigraphy. Flotation is a technique used by archaeologists to recover very small remains from an excavation. Systematic survey refers to the archaeological technique of systematically digging through the cultural and natural stratigraphy of an archaeological site.
Molecular dating uses an assumed constant rate of mutation to estimate the date of a most recent ancestor that is shared by two populations. Dendrochronology, or tree-ring dating, is a method of relative, and therefore unreliable, dating based on the study and comparison of patterns of tree-ring growth.
Get started today! Anthro Chapter 4. Edit a Copy. Study these flashcards. All of the following are true about the work of paleoanthropologists except that they. Informed consent refers to. What is paleopathology? The study of. Molecular anthropology. Systematic survey and excavation.
The principle of superposition states that in an undisturbed sequence of strata. Why do archaeologists use flotation? Which of the following is not one of the kinds of archaeology discussed in this chapter? Under what conditions are fossils most likely to form?
What term refers to the study of the processes that affect the remains of dead animals? The utility of stratigraphy for dating purposes is based on the fact that. Radiometric dating techniques available to anthropologists. Carbon dating is most accurate on specimens more than 70, years old.
What are both carbon and potassium-argon dating techniques based on? What kind of dating technique is fluorine absorption analysis?
The utility of stratigraphy for dating purposes is based on the fact that
What kind of absolute dating technique is used to date volcanic rock? Upon what assumption is molecular dating based? Physical anthropology and archaeology both involve multidisciplinary approaches to research. Palynology is the study of ancient animals through fossil remains.
Remote sensing refers to carrying out excavations in distant locations. Anthropometry is the study of human culture using satellite imagery. Paleopathology is the study of disease and injury in skeletons. Molecular anthropology studies evolutionary links using genetic analysis. Experimental archaeologists try to replicate ancient techniques under controlled conditions. Historical archaeologists use written records to supplement the archaeological record.
Colonial archaeologists study pre-Columbian cultures of the Americas. An early excavator of Hisarlik, Heinrich Schleimann, inadvertently dug through the Troy layer into an earlier occupation and mistakenly assigned the gold artifacts he found there to Troy.
Other sites have been continuously occupied by the same culture for a long time and the different layers represent gradual changes.
B ancient environments using samples of ancient
In both cases, stratigraphy will apply. A chronology based on stratigraphy often can be correlated to layers in other nearby sites. For example, a particular type or pattern of pottery may occur in only one layer in an excavation. If the same pottery type is found in another excavation nearby, it is safe to assume that the layers are the same age.
Archaeologists rarely make these determinations on the basis of a single example. Usually, a set of related artifacts is used to determine the age of a layer. Seriation simply means ordering. This technique was developed by the inventor of modern archaeology, Sir William Matthew Flinders Petrie.
Seriation is based on the assumption that cultural characteristics change over time. For example, consider how automobiles have changed in the last 50 years a relatively short time in archaeology.
Automobile manufacturers frequently introduce new styles about every year, so archaeologists thousands of years from now will have no difficulty identifying the precise date of a layer if the layer contains automobile parts.
Cultural characteristics tend to show a particular pattern over time. The characteristic is introduced into the culture for example, using a certain type of projectile point for hunting or wearing low-riding jeansbecomes progressively more popular, then gradually wanes in popularity.
The method of seriation uses this distinctive pattern to arrange archaeological materials into a sequence. However, seriation only works when variations in a cultural characteristic are due to rapid and significant change over time. It also works best when a characteristic is widely shared among many different members of a group.
Even then, it can only be applied to a small geographic area, because there is also geographic variation in cultural characteristics. For example, 50 years ago American automobiles changed every year while the Volkswagen Beetle hardly changed at all from year to year.
Cross dating is also based on stratigraphy. It uses the principle that different archaeological sites will show a similar collection of artifacts in layers of the same age. Sir Flinders Petrie used this method to establish the time sequence of artifacts in Egyptian cemeteries by identifying which burials contained Greek pottery vessels. These same Greek pottery styles could be associated with monuments in Greece whose construction dates were fairly well known.
Since absolute dating techniques have become common, the use of cross dating has decreased significantly. Pollen grains also appear in archaeological layers. They are abundant and they survive very well in archaeological contexts. As climates change over time, the plants that grow in a region change as well. People who examine pollen grains the study of which is known as pollen analysis can usually determine the genusand often the exact species producing a certain pollen type.
Archaeologists can then use this information to determine the relative ages of some sites and layers within sites. However, climates do not change rapidly, so this type of analysis is best for archaeological sites dating back to the last ice age. Absolute Dating Methods. Absolute dating methods produce an actual date, usually accurate to within a few years.
This date is established independent of stratigraphy and chronology. If a date for a certain layer in an excavation can be established using an absolute dating method, other artifacts in the same layer can safely be assigned the same age. Dendrochronology, also known as tree-ring dating, is the earliest form of absolute dating. This method was first developed by the American astronomer Andrew Ellicott Douglas at the University of Arizona in the early s.
Douglas was trying to develop a correlation between climate variations and sunspot activitybut archaeologists quickly recognized its usefulness as a dating tool. The technique was first applied in the American Southwest and later extended to other parts of the world. Tree-ring dating is relatively simple. Trees add a new layer of cambium the layer right under the bark every year. The thickness of the layer depends on local weather and climate.
In years with plenty of rain, the layer will be thick and healthy. Over the lifetime of the tree, these rings accumulate, and the rings form a record of regional variation in climate that may extend back hundreds of years.
Since all of the trees in a region experience the same climate variations, they will have similar growth patterns and similar tree ring patterns. One tree usually does not cover a period sufficiently long to be archaeologically useful. However, patterns of tree ring growth have been built up by "overlapping" ring sequences from different trees so that the tree ring record extends back several thousand years in many parts of the world.
The process starts with examination of the growth ring patterns of samples from living trees. Then older trees are added to the sequence by overlapping the inner rings of a younger sample with the outer rings of an older sample.
Older trees are recovered from old buildings, archaeological sites, peat bogs, and swamps. Eventually, a regional master chronology is constructed. When dendrochronology can be used, it provides the most accurate dates of any technique. In the American Southwest, the accuracy and precision of dendrochronology has enabled the development of one of the most.
Often events can be dated to within a decade. This precision has allowed archaeologists working in the American Southwest to reconstruct patterns of village growth and subsequent abandonment with a fineness of detail unmatched in most of the world.
Radiometric dating methods are more recent than dendrochronology. However, dendrochronology provides an important calibration technique for radiocarbon dating techniques. All radiometric-dating techniques are based on the well-established principle from physics that large samples of radioactive isotopes decay at precisely known rates. The rate of decay of a radioactive isotope is usually given by its half-life.
The decay of any individual nucleus is completely random. The half-life is a measure of the probability that a given atom will decay in a certain time. The shorter the half-life, the more likely the atom will decay. This probability does not increase with time. If an atom has not decayed, the probability that it will decay in the future remains exactly the same.
This means that no matter how many atoms are in a sample, approximately one-half will decay in one half-life. The remaining atoms have exactly the same decay probability, so in another half-life, one half of the remaining atoms will decay. The amount of time required for one-half of a radioactive sample to decay can be precisely determined. The particular radioisotope used to determine the age of an object depends on the type of object and its age. Radiocarbon is the most common and best known of radiometric dating techniques, but it is also possibly the most misunderstood.
It was developed at the University of Chicago in by a group of American scientists led by Willard F. Radiocarbon dating has had an enormous impact on archaeology. In the last 50 years, radiocarbon dating has provided the basis for a worldwide cultural chronology. Recognizing the importance of this technique, the Nobel Prize committee awarded the Prize in Chemistry to Libby in The physics behind radiocarbon dating is straightforward. Earth 's atmosphere is constantly bombarded with cosmic rays from outer space.
Cosmic-ray neutrons collide with atoms of nitrogen in the upper atmosphere, converting them to atoms of radioactive carbon The carbon atom quickly combines with an oxygen molecule to form carbon dioxide. This radioactive carbon dioxide spreads throughout Earth's atmosphere, where it is taken up by plants along with normal carbon As long as the plant is alive, the relative amount ratio of carbon to carbon remains constant at about one carbon atom for every one trillion carbon atoms.
Some animals eat plants and other animals eat the plant-eaters. As long as they are alive, all living organisms have the same ratio of carbon to carbon as in the atmosphere because the radioactive carbon is continually replenished, either through photosynthesis or through the food animals eat.
However, when the plant or animal dies, the intake of carbon stops and the ratio of carbon to carbon immediately starts to decrease. The half-life of carbon is 5, years. After 5, years, about one-half of the carbon atoms will have decayed.
The utility of stratigraphy for dating purposes is based on the fact that the potential for a much more precise subdivision of the stratigraphy and events within it. Using the high-resolution land-based cycle, isotope and magnetic record in the marine sediments and demonstrated the link between sequence and cycle stratigraphy. Radiometric dating generally involves measuring the ratio of the original because of analytical precision and utility with tuffaceous beds in marine or. (), the age uncertainty spans more than 10 million years depending on the to assess the utility of certain sections (age intervals) of the record for dating using features for stratigraphic and correlation purposes impossible at this stage.
After another 5, years, one-half of the remaining atoms will have decayed. So after 11, years, only one-fourth will remain. After 17, years, one-eighth of the original carbon will remain. After 22, years, one-sixteenth will remain. Radiocarbon dating has become the standard technique for determining the age of organic remains those remains that contain carbon. There are many factors that must be taken into account when determining the age of an object. The best objects are bits of charcoal that have been preserved in completely dry environments.
The worst candidates are bits of wood that have been saturated with sea water, since sea water contains dissolved atmospheric carbon dioxide that may throw off the results. Radiocarbon dating can be used for small bits of clothing or other fabric, bits of bone, baskets, or anything that contains organic material.
There are well over labs worldwide that do radiocarbon dating.Stratigraphy -- Reading Earth's History
In the early twenty-first century, the dating of objects up to about 10 half-lives, or up to about 50, years old, is possible. However, objects less than years old cannot be reliably dated because of the widespread burning of fossil fuels, which began in the nineteenth century, and the production of carbon from atmospheric testing of nuclear weapons in the s and s.
Another problem with radiocarbon dating is that the production of carbon in the atmosphere has not been constant, due to variation in solar activity. For example, in the s, solar activity dropped a phenomenon called the "Maunder Minimum"so carbon production also decreased during this period. To achieve the highest level of accuracy, carbon dates must be calibrated by comparison to dates obtained from dendrochronology. Calibration of Radiocarbon Dates.
Samples of Bristlecone pine, a tree with a very long life span, have been dated using both dendrochronology and radiocarbon dating. The results do not agree, but the differences are consistent.
That is, the radiocarbon dates were always wrong by the same number of years. Consequently, tree-ring chronologies have been used to calibrate radiocarbon dates to around 12, years ago.
When radiocarbon dating was first put into use, it was decided that dates would always be reported as B. That way, dates reported in magazine articles and books do not have to be adjusted as the years pass. So if a lab determines that an object has a radiocarbon age of 1, years inits age will be given as B. Calibrated dates are given using the actual date, such as c. Potassium-Argon Dating. If an object is too old to be dated by radiocarbon dating, or if it contains no organic material, other methods must be used.
One of these is potassium-argon dating. All naturally occurring rocks contain potassium. Some of the potassium in rocks is the radioactive isotope potassium Potassium gradually decays to the stable isotope argon, which is a gas. When the rock is melted, as in a volcano, any argon gas trapped in the rock escapes. When the rock cools, the argon will begin to build up. So this method can be used to measure the age of any volcanic rock, fromyears up to around 5 billion years old.
This method is not widely used in archaeology, since most archaeological deposits are not associated with volcanic activity. However, Louis and Mary Leakey successfully used the method to determine the ages of fossils in Olduvai Gorge in Tanzania by examining rocks from lava flows above and below the fossils.
They were able to establish an absolute chronology for humans and human ancestors extending back two million years. At Laetolli, in Tanzania, volcanic ash containing early hominid footprints was dated by this method at 3.
Other Methods. Uranium is present in most rocks. This isotope of uranium spontaneously undergoes fission. The fission fragments have a lot of energy, and they plow through the rock, leaving a track that can be made visible by treating the rock. So by counting fission tracks, the age of the rock can be determined. Like potassium-argon datingthis can only be used to determine the age of the rock, not the age of the artifact itself.
Thermoluminescence is a recently developed technique that uses the property of some crystals to "store" light. Sometimes an electron will be knocked out of its position in a crystal and will "stick" somewhere else in the crystal. These displaced electrons will accumulate over time.
If the sample is heated, the electrons will fall back to their normal positions, emitting a small flash of light. By measuring the light emitted, the time that has passed since the artifact was heated can be determined. This method should prove to be especially useful in determining the age of ceramics, rocks that have been used to build fire rings, and samples of chert and flint that have been deliberately heated to make them easier to flake into a projectile point.
Science continues to develop new methods to determine the age of objects.
has clearly demonstrated the utility of this approach to stratigraphic interpretation in Seriation is a relative dating technique that orders artifact attributes into a series based on frequency changes in either stylistic or functional attributes. C. the stratigraphic techniques are useful only if the soils have a high content of The utility of stratigraphy for dating purposes is based on the fact that. The utility of stratigraphy for dating purposes is based on the fact that Which of the following statements about techniques used in dating fossil remains is not.
As our knowledge of past chronologies improves, archaeologists will be better able to understand how cultures change over time, and how different cultures interact with each other. As a result, this knowledge will enable us to achieve a progressively better understanding of our own culture.
Baillie, M. London U. Taylor, R. Radiocarbon Dating : An Archaeological Perspective. Orlando, FL: Academic Press, Long, and R. New York : Springer-Verlag, Wood, Michael. In Search of the Trojan War.
New York : New American Library, Dating techniques are procedures used by scientists to determine the age of an object or a series of events. The two main types of dating methods are relative and absolute. Relative dating methods are used to determine only if one sample is older or younger than another. Absolute dating methods are used to determine an actual date in years for the age of an object. Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.
The main relative dating method is stratigraphy pronounced stra-TI-gra-feewhich is the study of layers of rocks or the objects embedded within those layers. This method is based on the assumption which nearly always holds true that deeper layers of rock were deposited earlier in Earth 's history, and thus are older than more shallow layers. The successive layers of rock represent successive intervals of time. Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers. If a certain kind of pollen is found in an archaeological site, scientists can check when the plant that produced that pollen lived to determine the relative age of the site.
Absolute dating methods are carried out in a laboratory. The most widely used and accepted form of absolute dating is radioactive decay dating. Radioactive decay dating. Radioactive decay refers to the process in which a radioactive form of an element is converted into a nonradioactive product at a regular rate.
The main relative dating method is stratigraphy. . It is based on the fact that trees produce one growth ring each year. .. between climate variations and sunspot activity, but archaeologists quickly recognized its usefulness as a dating tool. The utility of stratigraphy for dating purposes is based on the fact that. A. all environmental forces leave behind the same kind of soil deposit. B. the depth and . The utility of stratigraphy for dating purposes is based on the fact that A. radioactive decay B. stratigraphic associations C. reversals of magnetic fields D.
The nucleus of every radioactive element such as radium and uranium spontaneously disintegrates over time, transforming itself into the nucleus of an atom of a different element.