Carbon dating

Context: The Allahabad High Court ordered scientific survey that includes Carbon dating of a ‘Shivling’, found at the Gyanvyapi mosque complex in Varanasi.

Radiocarbon Dating Pioneer

• An American physical chemist, Willard Libby spearheaded a group of scientists in devising a technique to gauge radiocarbon activity.
• He is acknowledged as the first scientist to propose the existence of the unstable carbon isotope known as radiocarbon or carbon-14 within living organisms. 
•  He measured the rate of decay of radiocarbon and established a half-life of 5568 years ± 30 years. 
• In recognition of his contributions to the development of radiocarbon dating, Mr. Libby was honoured with the Nobel Prize in Chemistry in 1960.

Carbon dating

• The most prevalent carbon isotope in the atmosphere is C-12, while a small amount of C-14 is also present. The ratio of C-12 to C-14 in the atmosphere remains relatively constant.
• Plants obtain carbon through photosynthesis, and animals primarily acquire it from their diet. As plants and animals derive their carbon from the atmosphere, they accumulate C-12 and C-14 in a similar proportion to what is available in the atmosphere. 
• When they die, their interaction with the atmosphere ceases. While C-12 remains stable, the radioactive C-14 undergoes a process called “half-life,” wherein it reduces to half its initial amount in approximately 5,730 years.
• Carbon-14 serves as an isotopic timekeeper. By measuring the amount of carbon-14 present in a sample and comparing it to an internationally recognized reference standard, an approximate age can be determined. 

Significance

• It stands as a ground breaking scientific method that has not only transformed our comprehension of the present but has also unravelled events that occurred thousands of years ago. 
• Archaeology and various fields within the realm of human sciences heavily rely on radiocarbon dating to validate or refute theories. 
• Moreover, throughout the years, carbon-14 dating has found practical applications in diverse disciplines such as geology, hydrology, geophysics, atmospheric science, oceanography, paleoclimatology, and even biomedicine.

Limitations

While carbon dating is highly reliable, it does have limitations in its applicability.

• For instance, it cannot be employed to ascertain the age of inanimate objects like rocks. 
• Carbon dating is not suitable for determining the age of items that exceed approximately 40,000-50,000 years. The majority of rocks of interest surpass this timeframe. 
• This restriction arises from the fact that, after undergoing 8-10 half-life cycles, the quantity of C-14 becomes exceedingly minuscule and becomes nearly undetectable. 

Alternative methods

Alternative methods exist for determining the age of inanimate objects, many of which operate on the same principles as carbon dating. Instead of carbon, the decay of other radioactive elements present in the material serves as the basis for these dating techniques.

• Potassium-Argon dating: Radioactive isotope of potassium decays into argon, and analysing their respective ratios provides insights into the age of rocks. 
• Uranium-Thorium-Lead dating: They possess multiple radioactive isotopes, all of which decay into stable lead atoms. By measuring the ratios of these elements within a material, estimates about its age can be derived.
• Cosmogenic Nuclide dating: 

• Additionally, there are techniques to determine the duration of an object’s exposure to sunlight.
• These methods employ different approaches but are also based on radioactive decay, making them particularly valuable for studying buried objects or changes in topography.
• One commonly used technique is cosmogenic nuclide dating, or CRN, which is frequently applied to assess the age of ice cores in polar regions.
• Indirect use of Carbon dating method:

• The age of ice cores in glaciers and polar regions can be determined by examining the trapped carbon dioxide molecules within large ice sheets.
• These molecules have had no interaction with the external atmosphere and are preserved in the same state as when they were trapped.
• Estimating their age provides a rough approximation of when the ice sheets were formed. 

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