20091227

Astronomy final exam question: Venus vs. moon surface age

Astronomy 210 Final Exam, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

[20 points.] Discuss whether Venus' surface is older or newer than the surface of the moon, and the evidence that supports this claim. Explain by comparing surface features of Venus with the moon.

Solution and grading rubric:
  • p = 20/20:
    Correct. The number of impact craters on much greater on the moon, indicating its crust is much older than Venus', which has much fewer impact craters, having covered over much of its crust with extensive lava flows.
  • r = 16/20:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t = 12/20:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Recognizes importance of crater density, but may discuss how Venus' crust has more craters and thus is older, or correct choice for Venus' relative age, but crater discussion is problematic.
  • v = 8/20:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least recognizes that luminosity and temperature are relevant. May discuss Venus' atmosphere, runaway greenhouse effect, core, or other factors as evidence of its newer crust.
  • x = 4/20:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y = 2/20:
    Irrelevant discussion/effectively blank.
  • z = 0/20:
    Blank.
Grading distribution:
Section 70160
p: 23 students
r: 0 students
t: 14 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

Section 70158
p: 27 students
r: 4 students
t: 5 students
v: 5 students
x: 3 students
y: 1 student
z: 2 students

A sample "p" response (from student 1781):

An sample illustrated "p" response (from student 1964):

A more technical illusrated "p" response (from student 8260):

An sample "t" response (from student 6363), at least demonstrating the correlation between impact craters and surface age:

A sample "x" response (from student 2610), with a speculative guess followed by a sycophantic appeal:

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