The real meaning of history is to trace the developments in various fields of the human past. Towards this end, while investigating the past cultures, archaeology depends on various dating methods. These dating methods can broadly be divided into two categories, i. These are mainly non-scientific dating methods. These methods were relied on especially prior to the introduction of scientific methods of dating. But, even when the scientific methods of absolute dating are available, this method of dating has not lost its importance, as many a time we have to depend solely on relative dating.
A mass spectrometer is an instrument that uses a series of magnets to bend a beam of ions and then physically count how many there are, so with AMS radiocarbon dating, we can measure a carbon, 13 and 14 beam, and we measure the ratio of 14 to 13, and from that, we can tell how much C is in the sample.
So the most important things about AMS radiocarbon dating as opposed to conventional is that the sample size is much, much smaller. However, in many circumstances, sample size dictates AMS.
Geologists often need to know the age of material that they find. They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of Read our latest newsletter online here. 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.
Comparison of dating methods
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. 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. 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.
Dating methods. Dating techniques are procedures used by scientists to determine the age of a specimen. Relative dating methods tell only if one sample is older or younger than another sample; absolute dating methods provide a date in years. The latter have generally been available only since Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which . These methods were relied on especially prior to the introduction of scientific methods of dating. But, even when the scientific methods of absolute dating are available, this method of dating has not lost its importance, as many a time we have to depend solely on relative dating.
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. 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.
Wood, Michael. In Search of the Trojan War. New York : New American Library, Richmond, Elliot " Dating Techniques.
Richmond, Elliot "Dating Techniques. 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 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. In the process of disintegration, the atom gives off radiation energy emitted in the form of waves.
Hence the term radioactive decay. Each element decays at its own rate, unaffected by external physical conditions. By measuring the amount of original and transformed atoms in an object, scientists can determine the age of that object.
Cosmic rays: Invisible, high-energy particles that constantly bombard Earth from all directions in space. Dendrochronology: Also known as tree-ring dating, the science concerned with determining the age of trees by examining their growth rings.
Half-life: Measurement of the time it takes for one-half of a radioactive substance to decay. Radioactive decay: The predictable manner in which a population of atoms of a radioactive element spontaneously disintegrate over time. The age of the remains of plants, animals, and other organic material can be determined by measuring the amount of carbon contained in that material. Carbon, a radioactive form of the element carbon, is created in the atmosphere by cosmic rays invisible, high-energy particles that constantly bombard Earth from all directions in space.
When carbon falls to Earth, it is absorbed by plants. These plants are eaten by animals who, in turn, are eaten by even larger animals. Eventually, the entire ecosystem community of plants and animals of the planet, including humans, is filled with a concentration of carbon As long as an organism is alive, the supply of carbon is replenished.
When the organism dies, the supply stops, and the carbon contained in the organism begins to spontaneously decay into nitrogen The time it takes for one-half of the carbon to decay a period called a half-life is 5, years. By measuring the amount of carbon remaining, scientists can pinpoint the exact date of the organism's death.
The range of conventional radiocarbon dating is 30, to 40, years. With sensitive instrumentation, this range can be extended to 70, years. In addition to the radiocarbon dating technique, scientists have developed other dating methods based on the transformation of one element into another. These include the uranium-thorium method, the potassium-argon method, and the rubidium-strontium method. Thermoluminescence pronounced ther-moeloo-mi-NES-ence dating is very useful for determining the age of pottery.
The older the pottery, the brighter the light that will be emitted. Using thermoluminescence, pottery pieces as old asyears can be dated with precision. Tree-ring dating. This parallelism is formed due to trade relations, particularly wehen trade followed in both directions. For example, beads closely resembling those from the temple repositories at Cnoss and dating from C.
C were found in a late context Period V at Harappa. This closely agrees with the fact that the seals from Indus Valley style from Ur, Kish and Tell Asmar and other sites fall within the range of B. By noting the association of these beads it has been possible to trace a archaeological datum line across Indian sub-continent and Mesopotamia.
When a group or type of objects are found together under circumstances suggesting contemporanity they are said to be associated. It is nearly always association with other phenomena that gives a first clue as to the use, the age and chronological attribution of a potential datum, but age at least may sometimes be inferred from position in a geological deposit or a layer of peat.
Once a type has been classified by the aid of its context further specimen of the same type, even when found in isolation, can be assigned their place in terms of dates.
Association in simplicity can be illustrated by an example, at the port of Arikamedu near Pondicherry. Antiquities and potteries of Roman origin were found in association with the finds of Indian origin.
With the aid of these dated imports it was possible to date the associated Indian objects to the first two centuries A. Sometimes dates are also obtained with the assistance of astronomy. Clay tablets found in West Asia contain inscriptional evidence with regard to the occurrence of a solar eclipse. Specialists in the field of astronomical research placed this solar eclipse as on 15 th June B. The Almanac belonging to Maya culture of Central America helped in dating several important sites accurately on the basis of astronomy.
Astronomical data have been applied in the study of geological ice ages by calculating the curves for major fluctuation of solar radiation. Consequently, the chronology worked out for the geological deposits helped in dating the prehistoric tools found in these deposits.
There are certain antiquities and potteries which by themselves have acquired a dating value. Whenever and where ever such antiquities are found, associated finds are automatically dated. Sir Flinders Petrie had worked out a formula for dating the finds on the basis of the thickness of the deposit.
According to him a period of hundred years may be granted for the accumulation of a deposit of one and a half feet. However this formula has not been accepted by many archaeologists. Further this formula has been disproved on many occasions.
Pottery is probably the most abundantly available antique material in any archaeological site. It is based on the simple fact that industrial and art forms and for that matter all objects are subject to evolutionary process. Working out these changes brought in during the evolutionary process helps us in fixing chronological slots for different shapes.
Probability Comparison: Killing Methods
Examples may be cited from Greek archaeology where even the shapes of the pots have been appropriately and approximately dated. Similarly the forms of the pots of the Maya culture and the shapes and decorations on the Chinese potteries have been so adequately dated that their relative dating value is immense.
But in India though the variety of wares are satisfactorily dated the typological evolution is yet to be worked out. Houses, publica buildings and places of worship are also quite useful in providing relative dating. It is a common knowledge that the building and the building material of Harappan architecture are quite characteristic. Again the architectural feature of the building of th4e Sultanate period, Mughal period, Maratha period are quite distinct and have, therefore, accordingly been assigned different dates.
This is one of the most important methods of dating the ancient objects which contain some carbon in them. This method was discovered by Prof.
Willard F. Libby inwhich won him Noble Prize in Chemistry. This method has achieved fame within a short time largely because it provides chronology for the prehistoric cultures, when we do not have written records.
Scientific Explanation of this Therory :. This method is based on the presence of radio-active carbon of atomic weight 14 in organic matter. Cosmic radiation produces in the upper atmosphere of the earth Neutron particles, some of which hit the atoms of ordinary Nitrogen. This is captured by the nucleus of the nitrogen atom, which gives off a proton and thus changing to Carbon This creation of new carbon atoms and then reverting to nitrogen has achieved a state of equilibrium in the long duration of the earths existence.
Thus the process of radio carbon present in the living organism is same as in the atmosphere. It is further assumed that all living animals derive body material from the plant kingdom, and also exhibit the same proportion of C material.
Therefore as soon as the organism dies no further radiocarbon is added. At that time the radioactive disintegration takes over in an uncompensated manner.
The C has a half-life of about years, i. In the disintegration process the Carbon returns to nitrogen emitting a beta particle in the process. The quantity of the C remaining is measured by counting the beta radiation emitted per minute per gram of material. Modern C emits about 15 counts per minute per gram, whereas Carbon which is years old, emits about 7.
Specimens for C Dating :. Specimens of organic material which can yield good amount of carbon can be collected for C dating.
Quantity of Samples:. Quantity of samples sent for radicarbon dating should be sufficient enough to give proper results. As quite a bit of sample is lost in the pre-pigmentation process one should try to collect as big sample as possible. Bones are generally affected by ground water carbonates and are therefore least reliable for dating. Charred bones are better preserved and are therefore relatively more reliable. Charcoal is best material specially if derived from short live plants.