10. The dark spots or maria on the surface of the Moon are primarily:

Answer:

(A) Plains of basalt. The other three answers were all ruled out long before Apollo 11, but the correct answer was not known. "Cold Moon" theorists such as Harold Urey believed that igneous rocks like basalt could not exist on the Moon, and so the discovery of basalt by Apollo 11 was a great defeat for them.

Click here to go to the next question.