Investigation of the floor of the Black Sea, a saltwater sea connected

Question

Investigation of the floor of the Black Sea, a saltwater sea connected with the Mediterranean Sea by a narrow channel and remote from other seas, has revealed deposits of freshwater shells dating from 5500 B.C. on an ancient shoreline. That shoreline lies 500 feet below the Black Sea's current level, and the sediment just above it contains the remains only of saltwater creatures. Scientists hypothesize that about 5500 B.C., seawater from the Mediterranean overflowed into the Black Sea basin.

Which of the following would it be most useful to ascertain in order to evaluate the scientists' hypothesis?

A. Whether the body of freshwater whose shoreline was uncovered was less than 500 feet deep

B. Whether the remains of saltwater creatures contained in the layers of sediment that lie just above the ancient shoreline differ significantly from those contained in the topmost of layers of sediment in the floor of the Black Sea

C. Whether any of the freshwater shells show indication of having been used as tools

D. Whether there are traces of an ancient shoreline of the Black Sea that lies significantly less than 500 feet below the sea's current level

E. Whether the remains of the saltwater creatures found in the sediment closely resemble the remains of Mediterranean saltwater creatures from the same period.

souvik101990 · Accepted Answer

Premises: 
The floor of the Black Sea has deposits only of FRESHWATER CREATURES, implying that -- at one time -- the Black Sea was composed of fresh water. 
The sediment just above the floor contains the remains only of SALTWATER CREATURES, implying that -- at some point -- the Black Sea was transformed from a freshwater body to a saltwater body..

Conclusion: Seawater from the Mediterranean Sea overflowed into the Black Sea basin, transforming the Black Sea from a freshwater body to a saltwater body..

For evaluate CRs, rephrase the answer choices as STATEMENTS. 
The rephrase of the correct answer choice will either STRENGTHEN or WEAKEN the conclusion.

Answer choice E, rephrased: 
The remains of the saltwater creatures found in the sediment closely resemble the remains of Mediterranean saltwater creatures from the same period. 
This rephrase establishes a link between MEDITERRANEAN SEA and the SALTWATER CREATURES whose remains have been found in the Black Sea, STRENGTHENING the conclusion that seawater from the Mediterranean Sea overflowed into the Black Sea basin.

The correct answer is E.

kinjiGC · Answer

Investigation of the floor of the Black Sea, a saltwater sea connected with the Mediterranean Sea by a narrow channel and remote from other seas, has revealed deposits of freshwater shells dating from 5500 B.C. on an ancient shoreline. That shoreline lies 500 feet below the Black Sea's current level, and the sediment just above it contains the remains only of saltwater creatures.  Scientists hypothesize that about 5500 B.C., seawater from the Mediterranean overflowed into the Black Sea basin .

Which of the following would it be most useful to ascertain in order to evaluate the scientists' hypothesis?

A. Whether the body of freshwater whose shoreline was uncovered was less than 500 feet deep -  This is per premise that shoreline lies at 500 ft.

B. Whether the remains of saltwater creatures contained in the layers of sediment that lie just above the ancient shoreline differ significantly from those contained in the topmost of layers of sediment in the floor of the Black Sea -  There is no mention of Mediterranean Sea sediments

C. Whether any of the freshwater shells show indication of having been used as tools -  Completely OFS

D. Whether there are traces of an ancient shoreline of the Black Sea that lies significantly less than 500 feet below the sea's current level 
 We need to know if there is any traces of Mediterranean sea in Black Sea sediments. It doesn't matter if the traces of shoreline is significantly less than 500 ft or at 500 ft.

E. Whether the remains of the saltwater creatures found in the sediment closely resemble the remains of Mediterranean saltwater creatures from the same period. -  Correct - provides the required data to determine

AdmitJA · Answer

This strategy is amazing.

I am bad in evaluate CR questions. Think this strategy will help me! Thanks souvik101990! Glad I posted this Q here.

Great explanation by both of you as well! +1

kinjiGC · Answer

One of the strategies which I use and was taught by e-gmat class was the variance test.

Whatever question is asked in the option , answer as Yes and again answer as No, the conclusion will be different in two cases. Variance means there will be a variation of the conclusion.

For example, lets take the correct option E) 
E) Whether the remains of the saltwater creatures found in the sediment closely resemble the remains of Mediterranean saltwater creatures from the same period.
lets say yes, there were remains -> Proves the hypothesis is correct.
Lets say No, there were no remains -> proves the hypothesis is incorrect.
So there is a variation of conclusion. Hence the correct answer.

Raihanuddin · Answer

Copying other expert's explanation from other forum is not a good practice unless we mention the name of that expert.

kinjiGC · Answer

Majority of explanations are provided by me. Are you pointing to me?

mridupawandas · Answer

The hypothesis that water from medeterrian flew to black sea would be more easily answered if we know any proof and option E presents one such proof like situation of whether the creature remains of the two seas bear any resemblance if answer is yes then yes water might have flown. This is the only choice asking about such possibility .Hence E is the answer.

shriramvelamuri · Answer

Phew.., took me 5 mins to answer the question, but got it right.

I wonder if there is a simpler or quicker way to answer questions of this kind. Questions such as this take a lot of time in the real GMAT. By the way what is the level of scoring for this question.

Thank you for posting such a nice question. A good brainer.

chesstitans · Answer

this question is hard b/c it is hard to catch the main idea of the argument, and how the option choices directly relate to the argument.

C and D are surely out of scope. 
B and E are closed, but A also is a trap.
A is actually irrelevant b/c of "body of fresh water whose shorelines", B is not good enough and B is not so clear to be an assumption.

KarishmaB · Answer

B sea is far from all other seas except M sea to which it connects by a narrow channel.
B sea's floor was investigated (dug up to see the composition of layers under the floor)
We found freshwater shells dating from 5500 B.C. on an ancient shoreline 500 ft below current floor level.
The layer just above this ancient shoreline had saltwater remains.

Hypothesis: About 5500 B.C., seawater from the Mediterranean overflowed into the Black Sea basin.

All data points toward it, right? B sea is connected to M sea only. Before 5500 BC, B sea had fresh water (so it must not have been connected to any sea at that time). Then M sea must have overflowed into it because of which it got seawater & seawater creatures.

What will help us evaluate whether it was M sea that overflowed into it around 5500 BC?

A. Whether the body of freshwater whose shoreline was uncovered was less than 500 feet deep

The depth of the body at that time is irrelevant.

B. Whether the remains of saltwater creatures contained in the layers of sediment that lie just above the ancient shoreline differ significantly from those contained in the topmost of layers of sediment in the floor of the Black Sea

We know that ancient shoreline has freshwater creatures and the layer just above it has seawater creatures. We already know there are different remains in the two layers.

C. Whether any of the freshwater shells show indication of having been used as tools

Irrelevant

D. Whether there are traces of an ancient shoreline of the Black Sea that lies significantly less than 500 feet below the sea's current level

Another ancient shoreline is irrelevant to this argument.

E. Whether the remains of the saltwater creatures found in the sediment closely resemble the remains of Mediterranean saltwater creatures from the same period.

Correct. To evaluate whether it was M sea that overflowed around 5500 BC, we need to know if the creatures in the two seas were similar after overflowing.
If they are similar, it increases the probability that M sea overflowed into B sea.
If they are not similar, it doesn't help our argument. It may not have been M sea that overflowed into B sea.

Answer (E)

jabhatta2 · Answer

Hi  souvik101990  - i though option C was legitimate.

If Yes - well, humans were the reason why the freshwater sea shells are at the bottom of the black sea 
If No -- this eliminates a possible alternative (possible alternative : humans were using sea shells as tools. Because of humans, you are seeing freshwater sea shells)

devendra.c · Answer

While your question wasn't directed towards me, I will give it a shot nonetheless

The hypothesis concerns the remains of seawater creatures - it tries to explain where these came from. Option C will help us figure out where the freshwater creatures (those lying beneath the seawters creatures' remains) came from. And that isn't going to help us validate the hypothesis. Hence, it's not C. On the other hand, E gives information that bridges the gap between the investigation's findings and the scientists' hypothesis. I hope that helps

PReciSioN · Answer

Isn't the main discrepancy between, the contrast between freshwater shells being found at a shoreline, and saltwater creatures above it. Can C work by suggesting that the freshwater shells were deposited by humans, and that the Black Sea was a saltwater sea all along?

Kavicogsci · Answer

AjiteshArun  can you explain why not B?

My understanding is B is wrong because we are comparing sediments just above the shoreline aka of seawater creatures with the one found in topmost layer of shoreline (floor of Black sea) aka freshwater shells - so this is wrong as we already know this. Why is this stated again then?

However I selected this interpeting as a comparison between seawater creatures just above shoreline vs current creatures on upper layers of black sea

AjiteshArun · Answer

Hi Kavicogsci,

I interpreted B exactly as you did. That is, option B is talking about:

1. Remains of saltwater creatures in the layer of sediment just above the ancient shoreline
and
2. Remains of saltwater creatures in the topmost layer of sediment

We don't select option B, because we are interested in two things: (a) establishing the source (show that the water came from the Mediterranean Sea) and (b) establishing the time (show that the overflow happened in 5500 BC).

Option B would tell us whether the saltwater creatures from just after 5500 BC and more recent saltwater creatures were similar or not. That doesn't establish the connection that we need between the Black Sea and the Mediterranean Sea in 5500 BC.

Option E does give us that connection. If the creatures (from the same time period) were similar, then it's more likely that the source was the Mediterranean Sea. If they weren't similar, it's possible that something else happened.

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Investigation of the floor of the Black Sea, a saltwater sea connected

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Investigation of the floor of the Black Sea, a saltwater sea connected

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