We as human beings, not only curious about the future but also the past. But how we can know about the past society? Archaeology is the branch of anthropology, which studies the past culture of society through the artifacts or materials remain. Archaeology helps to reconstruct and interpret the past society. For this, dating should be done. Dating is the scientific method to assign date to fossil and artifacts.
There are mainly two types of dating.
- Relative dating.
- Absolute dating
It is the method of dating which help to find out the relative age of fossil or artifacts in relation to others. It tells us which one is older. There are various kind of relative dating which are as follows:-
i. Stratigraphy
ii. Fluorine analysis
iii. Uranium test
iv. Nitrogen test
v. Typological sequences.
i. Stratigraphy
It is the simplest dating method which is based on the principle of superposition. When there is a deposit with different layers, those laid on the bottom considered as the oldest and the top one as the latest.
ii. Fluorine analysis.
The specific progressive chemical changes when the bone, teeth, etc are buried under the ground. With the time passes, there is progressive loss of nitrogen and the amount of fluorine increases. If two fossils are buried at the time and site, both should have the same amount of nitrogen and fluorine.
iii. Uranium test(U-test)
With time passes, bone or teeth buried underground will have more uranium. So there is a higher concentration of uranium in the older than others.
iv. Nitrogen test
This test is based on the amount of fluorine. As the teeth or bone has a higher amount of fluorine, the lesser the amount of nitrogen.
v. Typological sequences
In this method, the like looked objects are grouped in a linear sequence to form a series. This method are of different type, mainly they are
A. Biostratigraphic dating: it relies on patterns of fossil distribution in rock layers.
B. Seriation: alike artifacts are grouped.
2. Absolute dating
This method is also called the chronometric dating method which assign specific date for an archaeological artifacts. There are different kinds of chronometric dating :
i. Dendrochronology
ii. Paleomagnetic dating
iii. Radiocarbon dating
iv. Potassium-Argon dating
v. Fission track dating
vi. Thermoluminescence dating
vii. Electron spin resonance dating(ESR)
i. Dendrochronology
This method is also called tree-ring dating. It is based on the fact that there is a relationship between the annual growth ring of the tree and its width. And it is affected by the availability of water and temperature fluctuations. The tree ring increases per year.
ii. Paleomagnetic dating
This method is based on major periodic changes in the Earth's magnetic field. With the formation of rock, it records the magnetic field. This sequence of geometric patterns helps to date the rock.
iii. Radiocarbon dating
It is the most commonly used method. It is also called carbon-14 and c-14 dating. It is based on the fact that all the living matter possesses a certain amount of a radioactive form of carbon. After an organism dies, it no longer takes in any of the radioactive carbon. Carbon-14 decays at a slow and steady pace and reverts to nitrogen-14. The rate at which the caron decays-its half-life,-5,730 years.
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| Radiocarbon dating |
iv. Potassium-argon dating
It is based on the fact that potassium-40 decays into the gas argon-40 and calcium-40 at a known rate. Radioactive potassium's half-life is 1,330 million years. This method is used for potassium-rich minerals in rock.
v. Fission track dating
This method is based on the number of crystalline or glass-like minerals trace amounts of uranium-238, which is an unstable isotope. 238U decays at a slow and steady rate. This decay takes the form of fission, and each separate fission leaves a scar or track on the sample.
vi. Thermoluminescence dating
It is a radiometric method which is used to date artifacts containing crystalline minerals like pottery. The number of radioactive atoms in some kinds of rock, soil, and clay produces constant low amounts of background ionizing radiation. During the measurement of crystalline material, the process of thermoluminescence starts which emits a weak signal proportional to the radiation absorbed by the artifacts, which, in turn, varies with the age of the sample.
vii. Electron spin resonance dating(ESR)
It is another comparatively new radiometric dating method related to thermoluminescence. Unlike thermoluminescence dating, however, the sample is not destroyed with the ESR method, which allows the sample to be date more than once. It is based on the fact that background radiation causes electrons to dislodge from their normal positions in atoms and become trapped in the crystalline lattice of the material.
References :
1.Carol R. Ember, Melvin Ember, Peter N. Peregrine(2015). Anthropology(14th edition)
2. www.fossilized.org
3. www.wikipedia.com