Passage III

Earth's gravitational field extends both above and below Earth's surface. In Figure 1, both the value of this field, , and the average density, ρ, of matter within Earth are graphed versus distance, r, from Earth's center. In addi­tion, Figure 1 identifies 5 regions, each of which is located either above or below Earth's surface.

Figure 2 shows the percent of Earth's mass located within a given distance r from Earth's center. For example, 10% of Earth's mass is located within 2,300 km of Earth's center, 20% of Earth's mass is located within 2,900 km of Earth's center, and so on.

Figures adapted from A. M. Dziewonski and D. L. Anderson, "Pre­liminary Reference Earth Model."©1981 by Elsevier B.V.

18. On average, Earth’s crust is about 30 km thick. Based on Figure 2, the crust accounts for approximately what percent of Earth’s mass?

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

Looking at figure 2, a small grid on the abscissa corresponds to 200 km, so 30 km is only about 1/7 of this small grid;

It can be seen from figure 2 that the last measurement of the abscissa The ordinate corresponding to the small grid increases from 90% to 100%, so 400 km corresponds to 10% of the mass, then 30 km can only correspond to about 30÷400×10%=0.75%, so 1% of the F option closest