Cuesta College, San Luis Obispo, CA
A rock sample with an extremely old solidification age (as determined by radioactive dating) is heated until it is molten, and then cooled back down to a solid. Discuss what happens to its solidification age (as determined by radioactive dating), and explain why this happens. Explain your reasoning using properties of radioactive decay.
Solution and grading rubric:
- the solidification age of a rock is determined by comparing the amount of gaseous decay products to the amount of unstable radioactive isotopes in the sample; a higher ratio of gaseous products to unstable isotopes corresponds to a sample that had solidified a long time ago; and
- heating the rock until molten would release the gaseous decay products, such that when it cools back down to a solid, it would have nothing to compare to the unstable isotopes that remain in the sample, effectively giving it a zero solidification age.
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. One of the two points (1)-(2) correct, other is problematic/incomplete.
Nearly correct, but argument has conceptual errors, or is incomplete. Only one of the two points (1)-(2) correct, other is missing, or both are problematic.
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of radioactive decay.
Implementation/application of ideas, but credit given for effort rather than merit. Approach other than that of applying properties of radioactive decay.
Irrelevant discussion/effectively blank.
Sections 30882, 30883
Exam code: finalLd0c
p: 11 students
r: 13 students
t: 6 students
v: 10 students
x: 0 students
y: 1 student
z: 2 students
A sample "p" response (from student 3019):
Another sample "p" response (from student 5080):
A sample "v" response (from student 1107):