Astronomy clicker question: the cheerleader effect

Astronomy 10, Spring Semester 2007
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q4.3

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the beginning of their learning cycle:

[0.3 points.] What makes up the core of the Earth?
(A) Very hot liquid metal.
(B) Very hot solid metal.
(C) Very cold liquid metal.
(D) Very cold solid metal.

Student responses
Section 4136
(A) : 17 students
(B) : 14 students
(C) : 0 students
(D) : 0 students

Section 5076
(A) : 12 students
(B) : 5 students
(C) : 0 students
(D) : 0 students

Correct answer: (B).

The reason for this is the "cheerleader effect"--imagine an inverted pyramid of cheerleaders, where the bottom cheerleader has to support the weight of all the other cheerleaders on top of her.

Also there is a competition between temperature and pressure in the core of the Earth. Temperatures that are high enough will melt solid into liquid, while pressures that are high enough will squeeze liquids back into solids. In the outermost core, temperature wins over pressure, so the outer core is hot and liquid. In the innermost core, where it is squeezed from all sides by the outer core, mantle, and crust, pressure wins over temperature, so the innermost core is extremely hot, but under the immense pressures there, is solid!