An area where the earth's crust would be expected to be thin would be _____. under the Pacific Ocean in the Rocky Mountains under the Mississippi River in the plains region of the Midwestern U.S.
The Earth's crust is known to be very thin under the oceans - oceanic crust is around 5 kilometers thick, while the crust under landmasses can be up to 30 kilometers thick.
Among the options only one refers to the Oceanic Crust - "under the Pacific Ocean"- this is the correct answer. The rest is a continental crust.
Withing the body of text this question was provided for, you should be able to find the passage, "The oceanic crust is thinner and denser than the continental crust."
