What ihe basis for the determination of Uranium 238-Lead radiometric date of 1120 ma for granite
Wouldn't it be the ratio of U238 and lead in the granite?
I do not think so, i have actually answer the question explaing it in words but i am not sure of it as the question is confussing
I take it this is S103 TMA08 Q2(b) (10 marks) "The age of a granite can be determined using radiometric dating. Explain the basis for the determination of a 238U-Pb radiometric date of 1120 Ma for a granite."
The key word here is "explain". There is nothing to calculate.
The best source of information is the course books.
To determine the radiometric date of a granite using the 238U-Pb dating method, we need to understand the underlying principles of radiometric dating.
Radiometric dating is a technique used to estimate the age of rocks and minerals by measuring the abundance of certain radioactive isotopes and their decay products. In the case of the 238U-Pb dating method, uranium-238 (238U) is a radioactive isotope that decays over time to form lead-206 (206Pb) through a series of intermediate isotopes.
The basic principle behind radiometric dating is that radioactive isotopes decay at a constant rate known as their half-life. The half-life is the time it takes for half of the original parent isotope to decay into its daughter isotope. In the case of the 238U-Pb dating method, the half-life of uranium-238 is about 4.5 billion years.
Now, let's apply this principle to the determination of the 238U-Pb radiometric date of 1120 million years (Ma) for a granite. Assuming the granite contains uranium-238 and lead-206, we can measure the ratio of these isotopes in the sample.
Initially, when the granite formed, there was no lead-206 present, only uranium-238. As uranium-238 undergoes radioactive decay, it gradually transforms into lead-206. By measuring the ratio of uranium-238 to lead-206 in the granite sample, we can estimate the amount of time that has passed since the granite formed.
The specific calculation involves comparing the measured ratio of uranium-238 to lead-206 with the known decay constant for uranium-238. Through this comparison, we can determine the age of the granite.
It's important to note that radiometric dating is based on several assumptions, including the initial abundance of parent isotope, a closed system where no isotopes are added or removed, and constant decay rates. These assumptions are generally valid for most samples, but it's important to consider potential sources of error and uncertainty in the dating process.
In summary, the determination of a 238U-Pb radiometric date for a granite involves measuring the ratio of uranium-238 to lead-206 in the sample and using the known decay constant of uranium-238 to estimate the age of the granite.