Chapter 29, Problem 4TE

To determine

The isotopes preferred in dating very old rocks.

Answer to Problem 4TE

The isotopes preferred in dating very old rocks are Uranium-238 and Uranium-235.

Explanation of Solution

Radiometric dating is the process by which the concentrations of radioactive elements in rock structures are used to determine the age of the rock. The number of decayed atoms corresponds to how long the rock has been there, and it can be found out by knowing the half-life of the radioactive isotope. Carbon-14 is useful when the dating evet lasts approximately within $50000\text{years}$. For older materials, radioactive element such as Uranium is used. In order to find the age of old rocks, the radioisotope of Uranium called Ur-238 is used. As Uranium-238 decays into Lead-206 to become stable and uranium-235 becomes Lead-207 during radioactive decay, the concentrations of these two isotopes give an estimate of the age of the rocks.

Conclusion:

Therefore, the isotopes preferred in dating very old rocks are Uranium-238 and Uranium-235.