Astronomy final exam question: intelligent life in globular clusters?

Astronomy 210 Final Exam, spring semester 2012
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:

AmazonMia: Why is it unlikely that intelligent life exists in globular clusters?
DVOTA: [H]eavy elements necessary for life would be too rare in these old clusters.

Discuss why this answer is correct, and how you know this. Explain using the properties and evolution of stars, and the expected requirements for life and advanced technological civilizations.

*Source: http://answers.yahoo.com/question/index?qid=20100324143024AAtFJZg.

Solution and grading rubric:

• p = 20/20:
  Correct. Discuss how globular cluster stars are metal-poor having formed from essentially just hydrogen, and would either (a) lack metals to form terrestrial planets, or (b) not enough various elements would exist to form molecular building blocks for life forms. Or may instead discuss (c) why globular clusters are metal-poor.
  
• 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.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least demonstrates some understanding of requirements for life, and/or metallicity of stars.
  
• 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 30674
Exam code: finalN34r
p: 16 students
r: 0 students
t: 4 students
v: 7 students
x: 0 students
y: 1 student
z: 2 students

Section 30676
Exam code: final5t4R
p: 10 students
r: 0 students
t: 5 students
v: 13 students
x: 0 students
y: 4 students
z: 0 students

A sample "p" response (from student 1524) explains why metals are required for life:
A sample "p" response (from student 2448) discusses how metallicity of stars increases with each subsequent generation: