Carbon Dating: Overview, Questions, Preparation

Carbon-14 is constantly created when cosmic rays interact with nitrogen in the atmosphere. On creation, the radiocarbon forms radioactive carbon dioxide after rapid oxidation with oxygen. The resultant radioactive carbon dioxide then enters the global carbon cycle via the process of photosynthesis into plants. Animals consume this by eating plants.

Now, when the plant or animal dies, this exchange stops but the radioactive carbon remains in them. The concentration starts to decrease as the Carbon-14 undergoes decay. The calculation of carbon014 concentration remaining in the plant helps to determine the age of the plant. The older the sample, the lesser is the concentration.

The half-life of Carbon-14 is about 5,730 years, and hence the oldest of dates can be determined using carbon dating. The radioactive decay occurs at a specific rate based on the mass and atomic number of the decaying atoms.   

Measurement

Beta-counting devices were used initially for measuring the carbon-14 concentration in the sample. This method involved the counting of the amount of beta radiation that was emitted by the carbon-14 atoms in the decaying sample. Liquid scintillation counting was another method used back then. In this, the sample would be in a liquid form, and a scintillator was added, which produced a flash of light when it interacted with a beta particle. A vial consisting of the sample was passed between two photomultipliers, and only when both devices registered a flash of light, the count was made. Currently, accelerator mass spectrometry is the method used which is quicker in giving results and takes into account all the carbon-14 atoms in the sample. In this method, the carbon-14’s content is measured relative to the present carbon-12 and carbon-13 in it.

Carbon dating helps researchers to know more about our past civilisations and our environment. It allows researchers to dive into the past and determine the actual dates of anything and everything that is organic. This has been a very important breakthrough in the field of archaeology. Carbon dating can help identify the age of wood, pollen, leather, plant, and animal remains and what not.

Carbon dating also has applications in the field of geology, lake studies and sedimentology. At present, carbon dating is widely used in the dating of important greenhouse gases like carbon dioxide and methane.

About topic in particular class:

In the Unit 1 of Class 10 syllabus titled ‘Chemical Substances- Nature and Behaviour’, Carbon and its compounds is the topic under which carbon dating comes. The unit collectively has a weightage of 26 marks.

Illustrated examples:

1) Reactions involving creation of Carbon-14.

n + 147N → 146C+ p (n=neutron and p=proton)

14C + O2 → 14CO + O

14CO + OH → 14CO2 + H

2) Half-life of carbon-14

5,730 years

3) Limitation of Carbon dating

It cannot be used for samples older than 60,000 years.

Q. What does the term Carbon dating mean?

Q. What are other names for carbon dating?

Q. How accurate is carbon dating?

Q. How long does it take to date something using carbon dating?

Q. Why is accelerator mass spectrometry used in modern times?