Scientists hypothesized that the end of a certain geological period ca

Question

Scientists hypothesized that the end of a certain geological period came about when a cataclysmic meteor impact near the equator caused debris to fly up into the atmosphere, where it was scattered by winds, blocking out the sunlight and abruptly killing off many species.
In European rock layers, the fossil record of the boundary layer that marks the end of the period supports this picture of rapid, mass extinction of life. But the boundary layer in the Antarctic is much thicker, so that it appears that the extinction process there lasted a much longer time, contrary to what the hypothesis would have predicted.

Which one of the following, if true, resolves the apparent discrepancy noted above?
(A) Although scientists have traditionally used the last appearance of creatures called ammonites to define the boundary layer, they recently found ammonites 20 meters above the previously identified boundary layer in the Antarctic.

(B) It was recently discovered that Europe accumulated sediment at a slower rate than did the Antarctic region, so that a layer of sediment of a given thickness represents a longer period of time in Europe than it does in the Antarctic.

(C) The controversy over whether the mass extinctions at the end of the geological period resulted from the impact of a meteor began only in 1979.

(D) The findings in Europe agree with data about the boundary layer from all other mid-latitude sites.

(E) The rock layers in the Antarctic were examined many years after the rock layers in Europe.

charanrana · Answer

Scientists hypothesized that the end of a certain geological period came about when a cataclysmic meteor impact near the equator caused debris to fly up into the atmosphere, where it was scattered by winds, blocking out the sunlight and abruptly killing off many species.

Given ->  In European rock layers, boundary layer less thick as compared with the boundary layer in the Antarctic, resulting in the extinction process at Antarctic lasting for more time, this is contrary to what the hypothesis predicted.

Which one of the following, if true, resolves the apparent discrepancy noted above?

(A) Although scientists have traditionally used the last appearance of creatures called ammonites to define the boundary layer, they recently found ammonites 20 meters above the previously identified boundary layer in the Antarctic.  -> This just gives us more information that the boundary layer is more thicker, but does nothing to resolve the apparent discrepancy

(B) It was recently discovered that Europe accumulated sediment at a slower rate than did the Antarctic region, so that a layer of sediment of a given thickness represents a longer period of time in Europe than it does in the Antarctic.  -> OK tells us why there is a difference in the thickness of the layers, looks good!

(C) The controversy over whether the mass extinctions at the end of the geological period resulted from the impact of a meteor began only in 1979.  -> Good to know but not useful for resolving the question!

(D) The findings in Europe agree with data about the boundary layer from all other mid-latitude sites.  -> We are bothered about the difference in thickness of the boundary layers at Europe vs at Antarctic and not worried about all the other equator regions

(E) The rock layers in the Antarctic were examined many years after the rock layers in Europe.  -> Does not matter, it is given that the boundary layer marks the end of the period, but there is no information that the boundary layer is still growing just because it is called "boundary", for all we know it might be buried under 100's of meters of rock, hence when it is measured is not going to help resolve the paradox

So only choice B looks good.

samiramir · Answer

Why B is the correct answer?

(B) It was recently discovered that Europe accumulated sediment at a slower rate than did the Antarctic region, so that a layer of sediment of a given thickness represents a longer period of time in Europe than it does in the Antarctic.

It should be exactly the opposite

nikitathegreat · Answer

@VeritasKarishma  GMATNinja  - Can you please explain this

bv8562 · Answer

Scientists hypothesized that the end of a certain geological period came about when a cataclysmic meteor impact  near the equator  caused debris to fly up into the atmosphere, where it was scattered by winds, blocking out the sunlight and abruptly killing off many species.

In European rock layers, the fossil record of the boundary layer that marks the end of the period supports this picture of rapid, mass extinction of life.  But the boundary layer in the Antarctic is much thicker, so that it appears that the extinction process there lasted a much longer time, contrary to what the hypothesis would have predicted .

Paradox : Since, the meteor impact occurred near the equator the European rock layers should have thicker boundary layer than the Antarctic rock layers. But it was found to be otherwise and this evidence goes against the hypothesis which is that the extinction process should have lasted a much longer time in Europe or countries near the equator leading to much thicker boundary layer.

(B) It was recently discovered that  Europe accumulated sediment at a slower rate than did the Antarctic region , so that  a layer of sediment of a given thickness represents a longer period of time in Europe than it does in the Antarctic . -  This resolves both aspect of the paradox i.e why European rocks have thin layer of sediment than Antarctic ones and how the thickness of the boundary is related to the duration of extinction process.

GMATNinja · Answer

The passage starts by giving us a hypothesis: a bunch of species were "abruptly" killed off by a certain meteor impact.

Then, we get a piece of evidence that goes  along  with this hypothesis: "In European rock layers, the fossil record of the boundary layer that marks the end of the period supports this picture of rapid, mass extinction of life."

Finally, we get a piece of evidence that seems to go  against  this hypothesis: the much thicker boundary layer in the Antarctic.

The question asks us to resolve the apparent discrepancy. In other words, how can we make it so that the hypothesis and the evidence all go together?

Here's (B):
 
(B) gives us a comparison between the two locations mentioned in the passage: Europe accumulates sediment  slower  than the Antarctic does. This is exactly the same as saying that Antarctica accumulates sediment  faster  that Europe does. Either way, the key piece of information is that  the same amount of time will produce a thicker layer in Antarctica than in Europe.

Remember that the boundary layer in Europe supports the meteor hypothesis. (B) doesn't change that fact -- it just gives us another way to think about the layer in the Antarctic compared to the one in Europe. Given the info in (B), it makes sense that the boundary layer would be thicker in Antarctica than in Europe, even if it was caused by the same abrupt event. Because the layer in Europe supports the hypothesis, we now have reason to believe that the layer in the Antarctic does as well.

(B) resolves the discrepancy and is the correct answer.

I hope that helps!

Scientists hypothesized that the end of a certain geological period ca

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Scientists hypothesized that the end of a certain geological period ca

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards