Given the information in the passage, to which one of the following would lichenometry likely be most applicable?

on June 1, 2018


Why is D right?


Christopher on June 3, 2018


Questions like this are often best approached through process of elimination. Lichenometry requires a number of boulders over a large area to remain in a set position for a length of time to gauge the speed of growth. Conditions like rain and shade also impact the growth rate, so the application of lichenometry is fairly specific and must be fairly large scale.

(A) looks at river flooding, but a flood would only move certain rocks in a small space and would also introduce many variables that would throw off the accuracy of lichenometry. So lichenometry wouldn't be useful.

(B) looks at a fossil, but lichenometry can only determine how long a particular surface has been exposed to sunlight. Lichenometry, then, could tell you how long the fossil had been uncovered but not when it was living. So it would not be useful.

(C) nothing suggests that lichenometry is feasible underwater.

(D) a receding glacier would expose new rocks to sunlight every year that it receded. Therefore, lichenometry could give scientists an idea of when stones all along the valley had first been exposed to sunlight, giving an estimate of the rate of recession of the glacier.

(E) nothing in the passage indicates that rainfall affects lichen growth or is detectable in the way lichen grows. Therefore, examining lichen would not help scientists identify anything about rainfall patterns.

I hope this helps.