Geologists recently discovered marks that closely resemble worm tracks

Question

Geologists recently discovered marks that closely resemble worm tracks in a piece of sandstone. These marks were made more than half a billion years earlier than the earliest known traces of multicellular animal life. Therefore, the marks are probably the traces of geological processes rather than of worms.

Which one of the following, if true, most weakens the argument?

Which one of the following, if true, most weakens the argument?

(A) It is sometimes difficult to estimate the precise age of a piece of sandstone.
(B) Geological processes left a substantial variety of marks in sandstone more than half a billion years before the earliest known multicellular animal life existed.
(C) There were some early life forms other than worms that are known to have left marks that are hard to distinguish from those found in the piece of sandstone.
(D) At the place where the sandstone was found, the only geological processes that are likely to mark sandstone in ways that resemble worm tracks could not have occurred at the time the marks were made.
(E) Most scientists knowledgeable about early animal life believe that worms are likely to have been among the earliest forms of multicellular animal life on Earth, but evidence of their earliest existence is scarce because they are composed solely of soft tissue.

Source: LSAT

broall · Answer

(A) It is sometimes difficult to estimate the precise age of a piece of sandstone.
 The difficuly to estimate the precise age of sandstone is irrelevant to the argument

(B) Geological processes left a substantial variety of marks in sandstone more than half a billion years before the earliest known multicellular animal life existed.
 This choice somewhat strengthens the argument.

(C) There were some early life forms other than worms that are known to have left marks that are hard to distinguish from those found in the piece of sandstone.
 This choice strengthens the argument since this choice indicates that if the marks are not the traces of geological processes, they are probably the traces of other life forms rather than of worms ( the probability that the marks are the traces of worms is really low ).

(D) At the place where the sandstone was found, the only geological processes that are likely to mark sandstone in ways that resemble worm tracks could not have occurred at the time the marks were made.
 Correct. This choice lefts out the possibility that the marks are the trace of geological processes.

(E) Most scientists knowledgeable about early animal life believe that worms are likely to have been among the earliest forms of multicellular animal life on Earth, but evidence of their earliest existence is scarce because they are composed solely of soft tissue.
 This choice is irrelevant to the argument.

XyLan · Answer

Conclusion:   
Marks are traces of GP( geological processes ) rather than of Worms.

Pre-thinking:  
Assumption: Traces of Worms/MultiCellularAnimals  CANNOT  pre-date the marking time on the sandstone.

Answer choice analysis of D and E:   
 (D)  At the place where the sandstone was found, the only geological processes that are likely to mark sandstone in ways that resemble worm tracks could not have occurred at the time the marks were made. 
  Meaning  : The GP(geological processes) that  could have marked  the sandstone  DID NOT  occur at the time when marks were  ACTUALLY  made.
 Let's say:  
Marks were marked on the sandstone in 1500 BC.
The GP( geological processes ) that could have marked did  NOT  occur in 1500 BC. 
 
Correct. This choice  REMOVES  the possibility that the marks are the trace of geological processes.
 
 (E)  Most scientists knowledgeable about early animal life believe that worms are likely to have been among the earliest forms of multicellular animal life on Earth,  but evidence of their earliest existence is scarce  because they are composed solely of soft tissue.
 
The  trap-answer : Evidence of their earliest existence is  scarce .
The scarcity of the evidence CAN sway in  BOTH  directions.   - Let's say further evidences are found.  
 Strengthen : 
Further evidence SHOWS that MultiCellularAnimals predate the marks. 
 Weaken : 
Further evidence DOES NOT SHOW that MultiCellularAnimals predate the marks.  
 
  TakeAway:  
 A  CORRECT  weakener should  NOT  affect the conclusion after many more assumptions.
Any answer choice which  CAN  sway in  BOTH  the directions is  NEVER  a correct answer.

Sneha333 · Answer

Please explain this..How can we assume about the place where sandstone was found was the place of origin for choice D.

XyLan · Answer

Sneha333 , A good thought!
However, even if one assumes that the place where sandstone was found was  NOT  the place of origin for choice D, i.e.,
 Let's say:  
The place of Origin - PofO
The place of Discovery - PofD  
The sandstone could STILL be  transferred  from PofO to PofD because of  natural events  such as floods, landslides, etc.   - A possibility

Even if we  assume  the above case(  PofO != PofD  ), it would  NOT  aid us in  weakening  the conclusion.
  Conclusion : Marks are traces of GP( geological processes ) rather than of Worms.
The geologists are  concerned  about the  causes  which could have led to those marking. 
They are contemplating the  probable  origins of the marks. It does  NOT  matter  whether  sandstone's Discovery was the same place as its Origin.

To answer this:  
 
Speaking for Option-D, I think the  thought process  behind this case(  PofO != PofD  ) was to look for  an alternate cause  such as: 
1) the marks could have happened in the PofO rather than in PofD.  & 
2) the reason for those marks  in PofO  should NOT be GP( geological processes )    - These things could have been true.   
However, a  lot of further  assumptions are involved in reaching this aspect, which would  NOT  be  correct  unless backed by a  coherent  answer choice.

TakeAway:   
A  correct  weakener:
 1) Should be a piece of NEW information.   - Not already stated/inferred.  
2) Needs to raise  a DOUBT  on the conclusion. It need  NOT  necessarily  destroy  the conclusion.

hero_with_1000_faces · Answer

You need to weaken the conclusion:
 Therefore, the marks are probably the traces of geological processes rather than of worms.

AND;

prove that: the marks are  not  the traces of geological processes.

Only D; fits the bill

unraveled · Answer

Geologists recently discovered marks that closely resemble worm tracks in a piece of sandstone. These marks were made more than half a billion years earlier than the earliest known traces of multicellular animal life. Therefore, the marks are probably the traces of geological processes rather than of worms.

Which one of the following, if true, most weakens the argument?

Which one of the following, if true, most weakens the argument?

(A) It is sometimes difficult to estimate the  precise age of a piece of sandstone . - WRONG. Irrelevant. 
(B) Geological processes  left a substantial variety of marks in sandstone more than half a billion years before  the earliest known multicellular animal life existed. - WRONG. Strengthens actually. 
(C) There were some early  life forms other than worms that are known to have left marks  that are hard to distinguish from those found in the piece of sandstone. - WRONG. Another possible reason for those marks 
(D) At the place where the sandstone was found, the only geological processes that are likely to mark sandstone in ways that resemble worm tracks  could not have occurred at the time the marks were made . - CORRECT. May be some other reason but not geological processes.
(E) Most scientists knowledgeable about early animal life believe that worms are likely to have been among the earliest forms of multicellular animal life on Earth, but evidence of their earliest  existence is scarce because they are composed solely of soft tissue . - WRONG. Somewhat strengthen rather but with certain assumptions are required to be made for that.

Answer D.

VerbalBot · Answer

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Geologists recently discovered marks that closely resemble worm tracks

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