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22 Feb 2022, 11:10
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woohoo921
I think that's fair. Would be curious other experts' thoughts on this though.
Anything that implied 'the water in the caves is different from rainwater that fell during that time' would be a possible explanation.
Quote:
Not quite sure what you're saying your mistake was. Are you saying you turned 'wood from trees in that time period have more deuterium than trees do today' into 'trees from that period had more deuterium than trees do today?'
That is the kind of subtle thing that can cost points. E, for instance, is onto something, but it's in the negated form. If deuterium-heavy wood is more likely to be preserved, it's not that old trees actually had more deuterium than trees today--we're dealing with a classic survivor bias (something the GMAT tests with some regularity).
So, yes--be careful about snapping what's written into something similar but crucially different. 'wood [remains] from that time have more deuterium than do trees today' is substantively different from 'trees from that time definitely had more deuterium than do trees today.'
14 Mar 2022, 11:41
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woohoo921
To start with your second point: even if an argument relies on an assumption, you don't want to just fill in that blank as if it's explicitly stated in the passage. If you do that, you're actually "fixing" the author's argument as you go, which will then make it impossible to accurately strengthen/weaken/etc. the argument that exists on the page.
Instead, just think about the structure of the argument as written, without filling in any gaps in the author's reasoning. That will prevent you from inserting your own assumptions as you did in this question.
Back to your first question: it's good to notice differences in language, and it's true that "water" can come from any source, whereas "rainwater" only comes from rain. But that in itself doesn't actually help us resolve the discrepancy.
Here's that discrepancy:
- On one hand, there's evidence that the rainwater available to trees 16000-24000 years ago had MORE deuterium than rainwater today
- On the other hand, the water in caves 16000-24000 years ago contains significantly LESS deuterium than rainwater in North America today.
Could this discrepancy be resolved by info explaining that the water came from two different sources? Sure! But your job is not to think of your own answer choice to resolve the discrepancy -- instead, your job is to assess the options given to you.
(D) resolves the discrepancy in a completely different way: both the caves and the trees were impacted by rainwater, but the rainwater in the caves is much older than the rainwater drunk by the trees. This helps us reconcile the two findings, and so (D) is the correct answer.
I hope that helps!
21 Sep 2022, 06:53
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Deuterium in Water
Step 1: Identify the Question
The question asks you to reconcile the two findings so this is an Explain the Discrepancy question.
Step 2: Deconstruct the Argument
Trees 16K-24K = more D
Cave water same time = less D
Step 3: Pause and State the Goal
On Discrepancy questions, your goal is to find a piece of information that makes the findings in the argument less surprising. It often helps to restate exactly what is surprising in the argument in your own words; it is strange that the trees and water from caves of the same age have different levels of deuterium. What would resolve this discrepancy?
Step 4: Work from Wrong to Right
(A) The argument is comparing deuterium from water in trees and caves. The fact that there is little deuterium in the caves aside from the water found there does not explain the different levels observed in caves and trees.
(B) This answer actually makes the finding more surprising. If the deuterium content increased after trees died, this might explain the higher deuterium content in wood. But if the level does not change, then it’s still unclear why the trees and caves from the same time period have different levels of deuterium.
(C) The argument compares the deuterium content in wood and cave water from several thousand years ago; anything that happened in the last 100 years is not relevant.
(D) CORRECT. This answer suggests that even though the trees and caves are of the same age, the water in the trees and the water in the caves may be of different ages (cave water may be thousands of years older). If the water is from different time periods, different levels of deuterium are less surprising.
(E) This information makes the findings even more puzzling. Only wood that remains preserved can be analyzed thousands of years later, so if high deuterium wood was more likely to be preserved that could explain the higher deuterium levels in wood. But if, as this answer states, wood with any level of deuterium can remain preserved, then it’s still not clear why the trees and caves from the same time period have different levels of deuterium.
Step 1: Identify the Question
The question asks you to reconcile the two findings so this is an Explain the Discrepancy question.
Step 2: Deconstruct the Argument
Trees 16K-24K = more D
Cave water same time = less D
Step 3: Pause and State the Goal
On Discrepancy questions, your goal is to find a piece of information that makes the findings in the argument less surprising. It often helps to restate exactly what is surprising in the argument in your own words; it is strange that the trees and water from caves of the same age have different levels of deuterium. What would resolve this discrepancy?
Step 4: Work from Wrong to Right
(A) The argument is comparing deuterium from water in trees and caves. The fact that there is little deuterium in the caves aside from the water found there does not explain the different levels observed in caves and trees.
(B) This answer actually makes the finding more surprising. If the deuterium content increased after trees died, this might explain the higher deuterium content in wood. But if the level does not change, then it’s still unclear why the trees and caves from the same time period have different levels of deuterium.
(C) The argument compares the deuterium content in wood and cave water from several thousand years ago; anything that happened in the last 100 years is not relevant.
(D) CORRECT. This answer suggests that even though the trees and caves are of the same age, the water in the trees and the water in the caves may be of different ages (cave water may be thousands of years older). If the water is from different time periods, different levels of deuterium are less surprising.
(E) This information makes the findings even more puzzling. Only wood that remains preserved can be analyzed thousands of years later, so if high deuterium wood was more likely to be preserved that could explain the higher deuterium levels in wood. But if, as this answer states, wood with any level of deuterium can remain preserved, then it’s still not clear why the trees and caves from the same time period have different levels of deuterium.
