The dating of remains is essential in archaeology, in order to place finds in and the less precise or relative chronology, as found in social and economic history, quantifiable methods such as dendrochronology and Carbon dating, over. The methods covered here are tried and tested, representing early methods of examining past geological, geographical, anthropological and archaeological.
Charred bones are better preserved and are therefore relatively more reliable. Charcoal is best material specially dwting derived from short live plants. How to collect samples: While collecting samples for dating methods in history carbon dating we should take utmost care, and should observe the following principles and methods. Sample should be collected from and undisturbed layer.
The method cannot provide an absolute age because the amount of fluorine differs from soil to soil, which gives a differential rate of absorption.
Like fluorine, uranium or nitrogen content of the bones also can be measured. Since fluorine and uranium levels in the bone increase with time, while nitrogen decreases, such measurements helps to place in sequence the cultural phases with which the different bones may be associated. In fact the analysis of fluorine, uranium or nitrogen is regarded as one of the very important technique for relative dating. Palaeontology - Palaeontology, the study of fossilised remains of bones in archaeological sites also provide relative dates.
The method is based on the fact that some animals migrate or become extinct with the change of climate. That is, climate has a direct relationship with the presence or absence of certain animals. For example, if evidence for Elephas antiques a forest elephant is found, one can assume a temperate climate, while the presence of E. Likewise, it is found that in North America the arrival of man caused the extinction of mammals such as the mammoth, horse, camel and several species of bison.
These can be dated approximately about B. C However, a margin of years error might be there as all of them have not become extinct at once and some have lived in isolated areas in which case the dating of fauna associated with other evidence is inexact and misleading. Smaller species of animals like rodents, birds, some molluscs and snails are found very sensitive to changes in climate than the larger mammals.
In Northern Ireland it has been possible to show changes in coastal environment since the time of human occupation by studying changes in tidal - zone molluscs found in archaeological sites. Palynology - Lennart Von Post, a Swedish Scientist, was the first to develop this palaeobotanical method in By this method a microscopic analysis of pollens extracted from trees are used to identify various trees and a pollen diagram is prepared. The pollen diagram in which relative frequencies of various species are plotted helps in tracing out the changing vegetation of an area.
Acid peat or bog deposit is ideal sources of animal pollen, but dry sites, and clays contain enough pollen to provide a sequence. Pollens in soil underlying or overlying archaeological sites may be correlated with the already known regional pollen sequence and the age of the site thus can be dated. A very good example of application of pollen method is the archaeological site at Choukoutien in China.
Patination - There is no precise definition for the term patination though it generally means chemical alteration of rock surfaces exposed to atmospheric conditions. The amount of patina on the stone is an index of its age valuable for relative placement of the stone artefact in the technological development.
The chemical alterations of the stone are usually brought about by the action of iron oxides through time. The observation of the amount of patina on a stone may be used at sites where there is a long sequence and demonstrates that those tools which lie in the bottom level may have more patina than those in the upper levels.
The different types of tools from the river gravels, terraces of rivers or lakes can be differentiated in the relative amounts of patina on the basis of which of the relative ages can be assigned on the artefacts. Goodwin who worked extensively on the patination in lists many variables involved in patina formation as well as different type of patination. That can be used fruitfully for the tools from stratified deposits.
Absolute Dating: Carbon Dating - Radiocarbon dating is a chemical analysis used to determine the age of organic materials based on their content of the radioisotope of carbon The method was developed by Willard F. Libby and a team of scientists at the University of Chicago. In Libby received the Nobel Prize for his method to use Carbon for age determinations in archaeology, geology, geophysics, and other branches of science.
It subsequently evolved into the most powerful method of dating and Holocene artefacts and geologic events up to about 50, years.
By radiocarbon method one can date different types of organic or inorganic materials as long as they consist of carbon. The method is actually devised to measure the amount of low level radioactivity of carbon remaining in ancient and dead material of organic origin.
Radiocarbon 14C dating is the most widely accepted technique for studying the chronological relationships of archaeological complexes. Using the radiocarbon method as a source of objective information, we are able to build Stone Age chronologies as well as establish the primary chrono-cultural boundaries.
The earth's crust contains potassium of which isotope K40 decays to A40 at a known rate. The ratio of potassium to Argon may be measured to ascertain date of minerals and rocks in a deposit. This method is able to cover a wide range of time even far greater than C method because, the half life of the radioactive potassium is million years.
The method has proved quite useful in dating some hominid fossils as employed in the site of Olduvai Gorge in east Africa where the remains were as old as 1. The advantage of the method is that it works well in case of the sites which are , years old.
But the disadvantage of the method is that it can be applied to only to those rocks and minerals which are rich in potassium. Therefore the method is restricted to the areas where volcanic rocks rich in potassium are available. Aitken and co- workers. Initially designed to date archaeological ceramics, it was subsequently extended to other mineral materials, such as burnt flint.
This is based on the fact that objects such as pottery that have been heated in the past can be dated by the measurement of their Thermoluminescence TL glow. Thermoluminiscence TL is the emitted light in the pottery which can be measured. If the ground up pottery is reheated, it emits light. The phenomenon results from radio-active influence of the metallic elements like uranium and potassium present in the clay and surrounding soils.
By the use of Thermoluminescence TL dating methods and the results obtained could make it possible to provide a new chronological framework for archaeological and anthropological knowledge. For example, the new chronology based on Thermoluminescence TL dating enabled in revising some prior assumptions about the evolution of lithic industries and the nature of hominids present in the Near East at various stages of the Middle Palaeolithic.
Dendrochronology - The age of wooden objects can be determined by means of Dendrochronology or tree ring analysis. It determines the calendar years of tree-ring formation and the felling dates of trees, which helps to determine the age of wooden objects with a great precision.
Dendrochronology has therefore become well established in the field of archaeology, art history and cultural heritage. The method depends on the fact that trees growing in temperate zones have clearly defined annual rings of growth.
As these tree rings represent annual growth, merely by counting rings one can count the age of the tree and hence its association. This dating method with latest methodological advances helps us in defining the calendar year in which the tree-rings were formed and in interpreting such dating in terms of the age of a wooden object. Despite many difficulties found for ESR dating of bones and carbonates, tooth enamel dated by Electron Spin Resonance ESR has been proven as a reliable method in its application to fossil teeth and quartz.
Both of the latter materials have allowed dating of Early and Middle Pleistocene sites which are not datable using other methods. In particular, recent discoveries of human remains in Western Europe have been proposed to be sites of the earliest arrival of humans there, and have been dated to the Early Pleistocene by Electron Spin Resonance ESR using quartz and tooth enamel.
Electron Spin Resonance ESR method can be applied to different types of samples in various environments; its contribution to the elaboration of a chronostratigraphic frame is of a great importance for the understanding of the Homo erectus dispersals out of Africa and especially for the first settlements in Europe. Palaeomagnetic Dating - It is an important means of crosschecking the dates based on the constantly shifting nature of the earth magnetic field, both in direction and intensity.
The measurement of the earth's magnetic field in several places of the world for centuries has shown that it varies with time. A number of studies have shown that a record of past magnetic field in the form of angles of declination and dip can be trapped in baked clay.
When clay is heated to a certain degree, the magnetic elements of baked clay realign themselves along lines dictated by the intensity and character of the magnetic field of the earth at that time. On cooling the magnetic elements are frozen and can be recorded as long as the clay is preserved. This is called remnant magnetism.
When records of past angles of declination and dip have been kept it is possible to compare the values of historic records and arrive at the date of archaeological specimens of fired clay. Fluxgate, Spinner magnetometer, Super-conduction magnetometer are the instruments used for measuring magnetic remenence. The method was used in Great Britain by Aitken in detail.
It has also been used in Japan and Arizona. In India the method is applied in dating Karewa sediments in Kashmir. The reliability of the application of the method depends on certain conditions such as The availability of good records of change of magnetic paths near the prehistoric sites, Occurrence of series of already dated baked clay in the area against which objects of unknown dates can be dated, Availability of archaeological samples which are found in their place of first occurrence.
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. Words to Know Cosmic rays: Invisible, high-energy particles that constantly bombard Earth from all directions in space.
Also known as tree-ring dating, the science concerned with determining the age of trees by examining their growth rings. 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. Study of layers of rocks or the objects embedded within those layers. 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.
Dendrochronology is a dating technique that makes use of tree growth rings. Reproduced by permission of The Stock Market.