Astronomy current events question: Australian oldest-known crust sample

Astronomy 210L, spring semester 2014
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Terry Devitt, "Oldest Bit of Crust Firms Up Idea of a Cool Early Earth," February 23, 2014
http://www.news.wisc.edu/22568

An international research term determined that an Australian crystal is the oldest-known crust sample by measuring the amount of lead produced by:
(A) ancient volcanoes.
(B) radioactive decay.
(C) cosmic rays.
(D) high magma temperatures.
(E) subterranean oceans.

Correct answer: (B)

Student responses
Sections 30678, 30679, 30680
(A) : 8 students
(B) : 19 students
(C) : 0 students
(D) : 16 students
(E) : 3 students