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Rock varnish ( iron and Mg)  due to bacteria
If cold, no bacteria


Cold Antartica : only of limonite, a form of oxidized iron  penetrated in cracks
Snow not melted and limonite needs water to move to move

Option: Moisture is required for the presence of significant amounts of manganese in the environment.
>> not mentioned

Option: Moisture is not required for the presence of significant amounts of manganese in the environment.
>> not mentioned

Option: When temperatures in a continuously frozen location increase to above freezing, cracks in rocks there begin to take in rock varnish containing significant amounts of manganese.
>> opposite mentioned: containing significant amounts of limonite-FALSE.

Option: Rock varnish that is especially rich in iron is mostly found in extreme cold.
>>not mentioned

Option: Manganese i s unable to penetrate into cracks in significant amounts.
>>not mentioned

Option: Temperatures on rocks in the Thiel Mountains were above freezing at some point in the past.
>>yes due to snow not stop yet-TRUE
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Quote:
Rock varnish is typically rich in iron and manganese, with the presence of manganese due to bacteria on the surface of the rock. Because the bacteria would not survive on the surface of rocks in the colder, continuously frozen, reaches of Antarctica, scientists were not surprised to discover that rock varnish in the Thiel Mountains area of Antarctica consists only of limonite, a form of oxidized iron. This had penetrated from the surfaces of the rocks into the cracks. However, although moisture is essential to the movement of limonite, snow has not melted in the Thiel Mountains in recent times.

Indicate which statement in the given information most strongly suggests is true, and the statement that the given information most strongly suggests is false. Make only two selections, one in each column.

TrueFalseStatements
Moisture is required for the presence of significant amounts of manganese in the environment.
Moisture is not required for the presence of significant amounts of manganese in the environment.
When temperatures in a continuously frozen location increase to above freezing, cracks in rocks there begin to take in rock varnish containing significant amounts of manganese.
Rock varnish that is especially rich in iron is mostly found in extreme cold.
Manganese is unable to penetrate into cracks in significant amounts.
Temperatures on rocks in the Thiel Mountains were above freezing at some point in the past.

True: Temperatures on rocks in the Thiel Mountains were above freezing at some point in the past.
False: When temperatures in a continuously frozen location increase to above freezing, cracks in rocks there begin to take in rock varnish containing significant amounts of manganese.



FALSE: When temperatures in a continuously frozen location increase to above freezing, cracks in rocks there begin to take in rock varnish containing significant amounts of manganese.- In the colder area, bacteria are absent , therefore manganese is absent hence no possibility of manganese in crack.

TRUE: Temperatures on rocks in the Thiel Mountains were above freezing at some point in the past , leading to the movement of limonite in the crack.
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Hope this helps!

Understanding the Passage
Key points:
  1. Rock varnish is usually rich in both iron and manganese.
  2. Manganese is deposited by bacteria, which cannot survive in cold, continuously frozen environments like Antarctica.
  3. In the Thiel Mountains, scientists did not find manganese — only limonite (oxidized iron).
  4. Limonite was found inside cracks, having penetrated from the surface.
  5. Moisture is needed for limonite to move.
  6. However, no snow has melted recently, so moisture hasn't been present in recent times.

Correct “True” Statement:
“Temperatures on rocks in the Thiel Mountains were above freezing at some point in the past.”
  • Why? Because moisture is needed for limonite to move into cracks.
  • And since limonite was found inside the cracks, moisture must have been present at some point.
  • But the passage says there has been no snowmelt in recent times, so that moisture must have come from older, warmer conditions — i.e., temperatures were above freezing in the past.

Correct “False” Statement:
“When temperatures in a continuously frozen location increase to above freezing, cracks in rocks there begin to take in rock varnish containing significant amounts of manganese.”
  • The passage tells us manganese comes from bacteria, and these cannot survive in the cold Antarctic environment.
  • Even if temperatures rise above freezing, unless bacteria are present, no manganese will be deposited.
  • So, just increasing the temperature is not sufficient for manganese-containing rock varnish to penetrate cracks.
  • Thus, this causal claim is not supported and is false.

sriharsha4444
KarishmaB ChiranjeevSingh AnishPassi GMATNinja can you take a stab at this very hard one. I am totally lost on this one
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parkhydel
Rock varnish is typically rich in iron and manganese, with the presence of manganese due to bacteria on the surface of the rock. Because the bacteria would not survive on the surface of rocks in the colder, continuously frozen, reaches of Antarctica, scientists were not surprised to discover that rock varnish in the Thiel Mountains area of Antarctica consists only of limonite, a form of oxidized iron. This had penetrated from the surfaces of the rocks into the cracks. However, although moisture is essential to the movement of limonite, snow has not melted in the Thiel Mountains in recent times.

Indicate which statement in the given information most strongly suggests is true, and the statement that the given information most strongly suggests is false. Make only two selections, one in each column.

Solving this question helps. Taking a timed set of similar questions in GMAT Club Forum Quiz → is even better.

KarishmaB MartyMurray ChiranjeevSingh DmitryFarber

I found this slightly confusing and wanted to verify that my thought process aligns with yours:



Attachment:
GMAT-Club-Forum-ja8vjznv.png
GMAT-Club-Forum-ja8vjznv.png [ 68.25 KiB | Viewed 1128 times ]
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Tucky


KarishmaB MartyMurray ChiranjeevSingh DmitryFarber

I found this slightly confusing and wanted to verify that my thought process aligns with yours:



Attachment:
GMAT-Club-Forum-ja8vjznv.png





Given:
Rock varnish is typically rich in iron and manganese
Manganese is present because of bacteria on the surface of the rock.
Bacteria would not survive on the surface of rocks in the colder, continuously frozen, reaches of Antarctica.
Scientists found rock varnish in Antarctica consists only a form of iron (makes sense since manganese wouldn't be found in continuously frozen places).
This iron had penetrated from the surfaces of the rocks into the cracks.
However, although moisture is essential to the movement of this iron, snow has not melted in the Thiel Mountains in recent times.


What this tells us is that iron had seeped into cracks and moisture (liquid water) is necessary for it. But in recent times snow has not melted so no liquid water. It means in the past snow must have melted into liquid water to make the iron seep into cracks. So temp must have been above freezing at that point.
Hence (F) is supported to be True.
(F) Temperatures on rocks in the Thiel Mountains were above freezing at some point in the past.


(C) When temperatures in a continuously frozen location increase to above freezing, cracks in rocks there begin to take in rock varnish containing significant amounts of manganese.
Also (C) is false because temperatures in a continuously frozen location do not allow manganese to be present (because they do not allow bacteria). So they cannot take in rock varnish containing significant amounts of manganese.
Hence (C) is supported to be False.


(D) Rock varnish that is especially rich in iron is mostly found in extreme cold.


Can't say. It could also be found in extremely hot, extremely rainy, extremely clean air places etc. Also, are we given that Antarctica has expecially rich in iron rock varnish? Not sure. We are given that it has only iron and no manganese, but is it especially rich in iron (more than usual), don't know.


(E) Manganese is unable to penetrate into cracks in significant amounts

Argument tells us nothing about whether manganese can penetrate rocks. We only know that limonite, a form of iron can.
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