Astronomy quiz question: cause of plate tectonics

Astronomy 210 Quiz 7, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[4.0 points.] What causes Earth's plate tectonics?
(A) Convection currents underneath the crust.
(B) Tidal forces from the moon.
(C) Gradual slowing rotation.
(D) Asteroid impacts that cracked the crust.

Section 70160
(A) : 28 students
(B) : 1 student
(C) : 0 students
(D) : 1 student

Correct answer: (A)

Lateral mantle flow below pulls the crust in certain directions; hot, rising magma produces new crust formation at midocean rifts; while cool, sinking magma occurs at subduction zones.

"Difficulty level": 94% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.13

Section 70158
(A) : 59 students
(B) : 4 students
(C) : 4 students
(D) : 1 student

"Difficulty level": 88% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33