Q19 - When a strone is trimmed

[ccalice21]

I can eliminate everything else to get B, but I don't see why it is correct.

I feel I don't really understand the question stem, how did the year 1492 suddenly appear in the conclusion?

Thanks a lot!

[giladedelman]

1492 is a somewhat arbitrary date here. The point is that since the organic matter is 1000 years old, and it must have grown shortly after the stone was trimmed, the monument that the stone is part of must be over 1000 years old. So it would have to be from further back than 1492. The conclusion could just as easily have said it was built before 1300, or 1650, or whatever.

Anyway, the gap here is that just because the stone must have been trimmed over 1000 years ago, that doesn't mean the monument is that old. What if the monument was made with trimmed stones that had been lying around for centuries? I'm sure the stone in my parents' fireplace is older than the plastic in their light fixtures; but both are part of the same house.

So (B) is correct because it would weaken the argument. If the reuse of ancient trimmed stones was common both before and after 1492, then we have no way to know when the monument dates from just because we know the age of a certain stone in that monument.

(A) is incorrect because the premise clearly states that the organic matter must have grown on the rock shortly after it was trimmed; we don't care whether it's from the varnish.

(C) is incorrect because the appearance is immaterial.

(D) is incorrect because the earliest written reference doesn't tell us how old the monument itself is.

(E) is incorrect because we don't really care about the pace of rock varnish growth. We care about the age of the rock as indicated by the organic matter.

Does that answer your question?