Question

Carbon-14 dating method is based on the fact that

• A. carbon-14 fraction is same in all objects
• B. carbon-14 is highly insoluble
• C. ratio of carbon-14 and carbon-12 is constant
• D. All of the above

Answer 1

The Correct Option is C

The Carbon-14 dating method, also known as radiocarbon dating, is primarily used to determine the age of archaeological and geological samples of organic origin. The key principle behind this dating method is the constant ratio of Carbon-14 to Carbon-12 in living organisms. Let's break down the concept:

1. Understanding Carbon Isotopes:
   • ^{12}C is the most abundant carbon isotope, making up about 99% of carbon found on Earth.
   • ^{14}C is a radioactive isotope of carbon which is naturally present in a small though constant amount in the atmosphere and living organisms.
2. Process of Carbon-14 Formation:
   • ^{14}C forms in the upper atmosphere through the interaction of cosmic rays with atmospheric nitrogen (^{14}N).
   • This newly formed ^{14}C combines with oxygen to form carbon dioxide, which is then absorbed by living organisms.
3. Constant Ratio Assumption:
   • While an organism is alive, the ratio of ^{14}C/^{12}C in its body remains roughly equal to the atmospheric ratio.
   • This is because living organisms are constantly interacting with their surroundings—taking in carbon through processes like photosynthesis or consumption.
4. Post-mortem Changes:
   • After the death of the organism, it no longer absorbs carbon from the environment.
   • The ^{14}C it contains starts to decay at a known rate (half-life of about 5730 years).
5. Dating Principle:
   • The decrease in the ^{14}C/^{12}C ratio over time enables scientists to determine the time since death.

Given these details, the correct answer to the question is: ratio of carbon-14 and carbon-12 is constant. This assumption underpins the accuracy and reliability of the Carbon-14 dating method.

Let's rule out the other options:

• Carbon-14 fraction is the same in all objects: This is incorrect, as ^{14}C levels differ in living organisms and atmosphere.
• Carbon-14 is highly insoluble: This is irrelevant to the radiocarbon dating principle.
• All of the above: This cannot be correct since only the constant ratio is accurate in context.