Astronomy current events question: Mars' habitable past

Astronomy 210L, Fall Semester 2010
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!)

Tom Beall, "Mars Was 'Recently' Habitable Planet," September 10, 2010
http://www.skyandtelescope.com/news/wires?id=149649139&c=y

What recent atmospheric data from the NASA Mars Phoenix lander may provide evidence that Mars was habitable enough for life within the past 100 million years?
(A) Fossil remnants of clouds.
(B) Carbon dioxide isotope proportions.
(C) Doppler radar of the upper atmosphere.
(D) Anomalous readings of the sun's intensity.
(E) Reflectance of dust storm particles.

Correct answer: (B)

Student responses
Sections 70178, 70186, 70200
(A) : 1 student
(B) : 25 students
(C) : 2 students
(D) : 1 student
(E) : 0 students