A fossil recently discovered in Marlandia, a chain of islands, proves

Question

A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged.

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.

B. Marlandia separated from a much larger landmass about eighty million years ago.

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.

D. The present-day reptiles are able to thrive on very tiny Marlandia islands.

E. The ancestral reptiles could not have survived long at sea.

CR02531.01

GMATIntensive · Accepted Answer

The Story     
 A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago.  - A fossil was recently discovered. The fossil links the lineage of a current reptile with an ancient reptile that lived in the same area many years ago.

The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago.   - The author is surprised by this finding since the ancient species was presumed to have become extinct when the area was submerged a few million years ago (The surprising part is that if the ancestral species had become extinct, how do we have its living descendants!)

Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged.  - Given this surprising finding, many scientists have concluded that the entire area must not have submerged (and thus the ancestral species may not have become extinct at that time.)

Gist:

The passage talks about certain reptiles in a particular chain of islands.

Recent development: A discovered fossil proves that a current species is descended from an ancient one.

Previous understanding: People used to believe that the islands had completely submerged in the past, making the ancient species extinct.

The coexistence of these two scenarios is surprising. (support) ,   Thus, many scientists conclude that the islands must not have entirely submerged (conclusion)  .

The Gap     
The argument assumes that  if the islands had entirely submerged, the species could not have survived.  What if the ancestral reptiles survived at sea? If the ancestral reptiles survived at sea, we’d have living descendant of the ancestral reptiles. In such a case, we’d have no basis to say that a part of Marlandia remained unsubmerged.

What if the ancestral reptiles migrated elsewhere, and then the descendants came back and resettled? In such a case too, we wouldn’t be able to arrive at the conclusion of the argument.

The argument also assumes that if an ancestral species goes extinct, it cannot have subsequent descendants. What if, there were some interim species that eventually led to the living descendants?

The Goal     
We’re looking for additional support for the scientists’ conclusion that the entire area must not have submerged. We can strengthen the argument by supporting any of the assumptions we figured above.

The Evaluation     
 A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise. 
  Incorrect  . Good for the reptiles! Did some adaptation come about from a complete submerge? Was there a complete submerge? Nothing here gives us a concrete answer for either of these questions.

B. Marlandia separated from a much larger landmass about eighty million years ago. 
  Incorrect  . How the islands came into being has got nothing to do with the argument at hand.

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia. 
  Incorrect  . Let’s consider the following statement:
Fossils of the  ancestral species  have been found at places  other  than Marlandia. (This statement is quite different from the one above, but stay with us a bit.)
Does this statement WEAKEN the argument?

It does. It indicates that the ancestral species perhaps relocated elsewhere and then the species or their descendants came back to Marlandia, thus making us doubt the hypothesis that the species must have survived in Marlandia itself, and thus weakening the conclusion that the islands must not have completely submerged.

Ok, let’s consider the following variation next:

Fossils that prove the relationship between the ancestral species and the present day species have been found at places other than Marlandia.

Does this statement WEAKEN the argument?

What does finding such fossils that ‘prove the relationship’ tell us? Do we know what type of fossils prove the relationship? Can only fossils of ancient reptile species prove this relationship? Couldn’t fossils of some other species help prove the relationship between the present-day and ancestral species? For example, couldn’t there be some indicative gene discovered in a fossil of species Z that helps prove a relationship between species X and Y? We do not know anything about what kind of fossils could prove the relationship. Thus this variation does not weaken the argument.

Now, let’s consider the option mentioned and discuss whether it STRENGTHENS the argument.

The fact that fossils that ‘prove the relationship’ haven’t been found does not increase our belief that the ancient species did not migrate (and as a consequence the belief that the sea-level rise left at least part of Marlandia unsubmerged.)

In addition, even if archaeologists were looking for such fossils, not finding does not equate to not being present. Fossils are difficult to find. Maybe they are out there, just that they haven’t been found yet.
 D. The present-day reptiles are able to thrive on very tiny Marlandia islands. 
  Incorrect  . Good for them! Happy to hear that the present-day reptiles are able to thrive. The argument is about whether the islands submerged and how the ancestral reptiles survived. This option does not support the argument at all.

E. The ancestral reptiles could not have survived long at sea. 
  Correct  . Had the islands been completely submerged, this option suggests, the ancestral reptiles could have gone extinct (since the possibility of surviving at sea is taken away). Since, in such a case, we wouldn’t find their descendants, an expectation that doesn’t match with the reality, it is likely that the islands were not completely submerged. This option does support the conclusion.

Additional Notes     
Remember: ‘To support’ does not mean ‘to confirm’. Option E does not confirm that the islands were not completely submerged. It does increase the probability, though.

If you have any doubts regarding any part of this solution, please feel free to ask.

GMATNinja · Answer

A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged.

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

First, let’s consider the structure of the passage:

Scientists conclude that  the sea-level rise 25 million years ago left part of Marlandia unsubmerged . 
 This is because a fossil proves that present-day Marlandian reptiles descend from ancient species that lived on the island millions of years ago. 
 Previously, the ancestral species was thought to have gone extinct during the sea-level rise.

But the scientists seem to have made a jump in their reasoning. Just because the species continued after the sea-level rise does not necessarily mean that part of Marlandia was unsubmerged. What if the ancient species survived the sea-level rise in another way?

The question asks that we find an answer choice that provides the most support for the scientists’ conclusion. With that in mind, let’s take a look at the answer choices.

(A) gives us information about what has happened since the sea-level rise, but we’re concerned with what happened during the sea-level rise. Moreover, it merely gives us information on reptiles in general, and we don’t know whether it applies to this particular species. Eliminate (A).

If Marlandia previously separated from a larger landmass, we may have some reason to believe that the ancient species was originally found on that landmass. But the fact that Marlandia separated from a larger landmass 80 million years ago gives us no reason to believe that Marlandia was left unsubmerged 25 million years ago. Eliminate (B).

(C) tells us that the only proof of a relationship between the ancient and present-day species has been found in Marlandia. This may make us think that the relationship between the two species is unique to the island. But we don’t actually know that for sure. All we know is that our existing proof only supports the relationship on Marlandia. And it still does not provide support for the idea that part of Marlandia was left unsubmerged. Eliminate (C).

The problem with (D) is that we don’t know whether the present-day reptiles are able to thrive on other islands as well. If they were only able to thrive on the tiny islands, then maybe we would have reason to believe that those islands were left unsubmerged. But we don’t actually know that, and it’s possible that the reptiles are able to thrive in many places. So, we can eliminate (D).

(E) is interesting. If the ancestral reptiles could not have survived long at sea, then we have reason to believe that the reptiles would not have survived if the entirety of the Marlandia islands were submerged. Because the reptiles did survive, (E) makes us think that at least part of Marlandia was unsubmerged. Therefore, (E) supports the scientists’ conclusion, and it is the best answer choice.

firas92 · Answer

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.

If the ancestral reptiles can adapt, then they probably made it through the sea level rise. Weakens

B. Marlandia separated from a much larger landmass about eighty million years ago.

Irrelevant since the sea level rise is thought to have happened only 25 million years ago

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.

Irrelevant

D. The present-day reptiles are able to thrive on very tiny Marlandia islands.

Irrelevant

E. The ancestral reptiles could not have survived long at sea.

If the ancestral reptiles could not have survived at sea and they have present day descendants, the ancestral reptiles probably didn't have to survive at sea. This should mean that some part of Marlandia wasn't submerged. Strengthens

Answer is (E)

Kanika3agg · Answer

A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged.

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

Conclusion - Some part of Marlandia was unsubmerged when the sea-level rose.
In all the answer choices, we have to find the strengthener of this statement.

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise. -  Doesnt say anything about conclusion.

B. Marlandia separated from a much larger landmass about eighty million years ago.  We are talking about 25 million years old issue here

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia. -  No talk about conclusion

D. The present-day reptiles are able to thrive on very tiny Marlandia islands. -  I initially marked this as it proves that the reptiles can survive even on tiny islands. so, take it as a contender

E. The ancestral reptiles could not have survived long at sea. -  This shows that reptiles would have to survive at land as it cant survive in sea for sure. So, this definitely proves our conclusion.

Out of D and E, E is a better choice.

gmatt1476 · Answer

Official Explanation

Argument Construction

This question requires that we identify the answer choice that lends the most support for the scientists' conclusion. This conclusion states that the islands of Marlandia must not have been completely submerged during a global rise in sea level as had previously been thought.

Scientists arrived at this conclusion after being surprised to find that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. They had believed that this prehistoric species had become extinct millions of years ago when Marlandia was submerged due to a global rise in sea level.

What are some ways that we can strengthen support for the conclusion? Information that rules out the possibility that the reptile could have survived even if the islands had been completely submerged would strengthen support. So would information that rules out the possibility that the reptile had migrated to somewhere other than Marlandia but traveled back to Marlandia after the islands were no longer submerged.

A. Even if it is true that reptiles on Marlandia have adapted to environmental changes since the sea-level increase, that does not support the belief that part of Marlandia never became submerged when the sea level rose. It does not rule out either of the two alternative explanations discussed immediately above, for instance.

B. The argument's conclusion is about whether some part of Marlandia never became submerged. Information indicating that Marlandia separated from a much larger landmass many millions of years before the global sea-level rise is not relevant to that conclusion.

C. It might seem that this choice supports the conclusion. If the ancestral species never lived anywhere other than Marlandia, then the present-day species could not have descended from this ancestral species elsewhere and only later, after the sea-level rise, migrated to Marlandia. That would help rule out an alternative explanation of how the present-day species survived the global sea-level rise. However, note that all we are told is that no fossils have been found anywhere other than Marlandia. Simply because no such fossils have yet been found does not indicate that these ancestral species never existed elsewhere. Fossils are often deeply buried and hard to find. After all, the fossils on Marlandia that are discussed in the argument were only recently found; perhaps other such fossils will soon be found elsewhere. Thus, this answer choice does not support the conclusion.

D. This does not provide any particular support for the argument. Note that it is not the present-day reptile species that is presumed to have survived on Marlandia when sea levels rose. Rather, it is the ancestral species that is presumed to have survived.

E. Correct. This rules out that the ancestral species could have survived the sea-level rise simply by living at sea. It also reduces the possibility that the ancestral species had also lived elsewhere than Marlandia and had only later—after the sea-level rise—migrated to Marlandia.

The correct answer is E.

KarishmaB · Answer

A fossil has been found in Marlandia, an island. 
It shows that an indigenous present day reptile descended from an ancient reptile that lived here (so perhaps the fossil has unique features of both).
This is surprising because the ancient reptile was though to have become extinct 25 million yrs ago when Marlandia got submerged.

Conclusion - Some parts were not submerged.

We need to strengthen this.

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.

Doesn't say anything about whether all of Marlandia could have been submerged or not.

B. Marlandia separated from a much larger landmass about eighty million years ago.

Irrelevant how Marlandia came into being.

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.

No fossils have been found elsewhere does not mean they don't exist elsewhere. We are not given that the ancient reptiles lives only on Marlandia. Perhaps the fossil reptiles came to Marlandia and then the present day reptiles descended from them. Though to a small degree, it does increase the probability that some parts of Marlandia were not submerged but finding fossils is such a rare occurrence that not finding elsewhere has little meaning. Let's hold this.

D. The present-day reptiles are able to thrive on very tiny Marlandia islands.

Irrelevant.

E. The ancestral reptiles could not have survived long at sea.

This does help to strengthen that some parts of Marlandia were not submerged. If the ancient reptile could not have survived long at sea, it could not have stayed in the sea and then come back to Marlandia when it rose up again. This also means the ancient reptile could not have swum somewhere else and then come back to Marlandia once it rose again. Hence, it does become more likely that some land of Marlandia must not have been submerged.

Also, now looking at option (C) again (while ignoring option (E)), we know that it doesn't strengthen the conclusion. The ancient reptile could have swum to other land and returned to Marlandia once it rose again. So not finding fossils elsewhere doesn't help us.

Answer (E)

Saupayan · Answer

Hi  GMATNinja ,
I agree with the  highlighted text  in your explanation for option C.
However, this is a strengthen question, not an assumption (or prove that without doubt) question.
"we don't know that for sure" : true, but do we need to? isn't the fact that it points to a certain direction good enough to strengthen? maybe later, we will be proven wrong, but for now, with the available data, isn't it a good enough strengthener?

Consider option E for example: 
 
Let's say this were true. We may think since the present-day species are descendants of the old-day species, they must have come from the old day species that were living on this island.  But we don’t actually know that for sure. All we know is that our existing proof supports there is a relationship between the old species from this very island and the new species on this island  It doesn't even consider the possibility that these species may have come from a different island.

For what it's worth, I picked option E because it just felt more straightforward. But, that is not a good way to go about answering questions 😅

GMATNinja · Answer

Let's start by taking a closer look at (C):

How would this affect our argument? Well, we already have a fossil which proves that the present-day reptile "indigenous to Marlandia" is descended from an ancient reptile species that lived on the island. What would (C) add to that? If (C) weren't true, would this really support the idea that the ancient species  lived  somewhere besides Marlandia?

Not really. Even if a fossil WERE found somewhere other than Marlandia, that wouldn't necessarily prove the ancient species  lived  there. Where is this hypothetical fossil exactly? And how did it get there? Notice it would take a leap to assume that this fossil PROVES that the ancient reptile was  living  on some other island. Maybe the fossil was found on the ocean bottom? Maybe it was transported somewhere when Marlandia was flooded?

Bottom line: for (C) to support the answer, we'd need to make some leaps that aren't airtight.

On the other hand, (E) supports the conclusion without a doubt. A possible objection to the argument would be that the ancient reptiles survived at sea. Notice that (E) unambiguously rules out this objection.

For those reasons, (C) is wrong, and (E) is a stronger answer.

I hope that helps!

Kavicogsci · Answer

Fossil found - relationship between an indigenous present day species of land with ancestor (lived on island million years ago)
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However those species were considered to be extinct when the island submerged (if no species, how can you have descendants - paradox)
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Part of island must have remain unsubmerged - so that a few species survived - hence proving our finding

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.
The passage talks about  A  present day reptile species (indigenous to island) who descended from  AN (implying a specific species).  The statement however talks about generic info on reptiles species(not the specific ancient one we are interested in) after sea rise which may not even be relevant to our context hence not useful to strengthen the link on why the island didnt fully submerge - leaving behind a few species. Reject

B. Marlandia separated from a much larger landmass about eighty million years ago.
It separated 80 million ago and then submerged 25 million years again - this doesn't convey anything needed to strengthen the partially unsubmerged part. Remember what we have to strengthen! Reject

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.
This looks defender strengthener but may not be so. Lets see it this away - if we assume that fossils that prove relationship between the two have been found other than Marlandia the argument still stays and is not weakened - maybe these reptiles were good swimmers went to a different island and their fossils were there. Then there was some sort of reverse migration to Marlandia island for the present reptiles so they are still descendants however we havent been able to establish the unsubmerged link. The island could have been submerged or not we can't say.

D. The present-day reptiles are able to thrive on very tiny Marlandia islands.
How does that help us establish the island unsubmerged link? Reject

E. The ancestral reptiles could not have survived long at sea. 
Exactly! Defender strengthener in the house - if the reptiles could have survived in sea then we have no reason to think that the island would have remained unsubmerged.

AjiteshArun  do you think my way of looking at C is fine?

AjiteshArun · Answer

Hi Kavicogsci,

Yes, your reasoning looks good! The scientists' conclusion would be strengthened if we know that (a) the ancient species wasn't present elsewhere and migrated (separately) to M at some point in the last 25 million years and (b) that the ancient species didn't migrate elsewhere and return to M at some point in the last 25 million years.

But it's very likely that the question wants to tell us that proof wasn't available earlier (before this recently discovered fossil). Given that, the information in option C doesn't really tell us much. In other words, I'd consider option E to be (far) stronger than option C.

kabirgandhi · Answer

Couldn't answer choice C, strengthen the argument by ruling out an alternative? If the relationship between ancestral reptiles and modern reptiles has only been established in Marlandia, then these reptiles could not have somehow descended from the ones on a nearby island/place and migrated here, hence at least part of Marlandia would have to be unsuberged for them to survive

GMATNinja · Answer

Finding such fossils elsewhere isn't necessarily a problem. The fossils might be less than 25 million years old (after the global sea-level rise) but contain some other evidence linking the present-day and ancestral species. Or perhaps the fossils originated in Marlandia but somehow ended up in a different place.

Also, only finding fossils in Marlandia still leaves a substantial gap in the logic: if the ancestral reptiles COULD HAVE survived long at sea, the argument falls apart. (E) fills that gap, so it definitely supports the scientists' conclusion. (C) might also support the scientists' conclusion, but only if we make some assumptions.

egmat · Answer

It's a classic strengthen question that trips up many test-takers. Let me walk you through how to approach this systematically.

Understanding What's Happening Here

First, let's get clear on the puzzle: Scientists found fossils proving that today's Marlandia reptiles descended from ancient reptiles. But here's the twist - everyone thought those ancient reptiles died out when the islands went underwater 25 million years ago. So how did their descendants survive?

The scientists' explanation: Some parts of Marlandia must have stayed above water during that sea-level rise.

Now you need to strengthen this conclusion.

The Key to Solving This

When strengthening an argument, think about what would make the conclusion  necessary  rather than just possible. Let's evaluate the most tempting choices:

Choice D : "Present-day reptiles can thrive on tiny islands"
This seems supportive - if modern reptiles don't need much land, maybe their ancestors survived on small dry patches. But notice how this doesn't really prove land  had  to stay dry. It's helpful but not compelling.

Choice E : "The ancestral reptiles could not have survived long at sea"
Here's your winner! If the ancient reptiles couldn't survive in water, and their descendants exist today, then  the only possible explanation  is that some land remained dry. This eliminates the main alternative (that they somehow survived total submersion) and makes the scientists' conclusion virtually certain.

Notice how Choice E creates logical necessity: If reptiles can't swim + descendants exist = land must have stayed dry. That's the kind of ironclad support you're looking for in strengthen questions.

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You can check out the  step-by-step solution on Neuron by e-GMAT  to master the complete framework for tackling strengthen questions systematically. The full solution reveals advanced techniques for quickly eliminating trap answers and identifying the logical gaps in arguments. You can also explore other GMAT official questions with detailed solutions on Neuron for structured practice  here .

jonazx44 · Answer

Wouldn't B also strenghten by eliminating an alternative? If there was a big landmass right next to the islands, the reptiles could have simply moved there, and the islands could have stayed totally submerged... I get why E is stronger as its a more basic assumption, but could this answer be correct if we didnt have E?

egmat · Answer

Your Thinking is Valid 
You're right - eliminating alternatives IS a valid way to strengthen. Good GMAT instinct.

But B Doesn't Work 
B says Marlandia separated from a landmass  80 million years ago .
Sea-level rise was  25 million years ago .
That's a  55-million-year  gap. B tells us nothing about what other landmasses existed at the time of the flood. Too distant in time to matter.

Why E is Correct - The Full Picture 
The scientists' logic: Reptiles alive today → Must have survived the flood → Land must have existed

But what's the GAP?

Scientists assume the ONLY way to survive is on land. But what if:
 
 They swam to safety? 
 They floated on debris? 
 They survived in water until land reappeared?

If any of these work, reptiles survive even if Marlandia was  fully submerged . Conclusion falls apart.

What E does: 
E slams the door shut: "Ancestral reptiles could not have survived long at sea."
 
 Can't swim to safety ❌ 
 Can't float on debris ❌ 
 Can't wait it out in water ❌

Now the logic is airtight:
Couldn't survive water + Did survive =  MUST  have had land
E doesn't just support the conclusion. It makes the conclusion  the only possible explanation .

A fossil recently discovered in Marlandia, a chain of islands, proves

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GMAT Critical Reasoning (CR) Questions

A fossil recently discovered in Marlandia, a chain of islands, proves

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