fangtray wrote:His studies of ice-polished rocks in his Alpine homeland, far outside the range of present-day glaciers, led Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets had existed in now currently temperate areas

Why does had existed not work here? these ice sheets existed in the past...and Louis proposed this concept in the past. SO how come past past tense doesn't work?

Please post the options along with the question, before your query on the same.

Thanks,
GK

His studies of ice-polished rocks in his Alpine homeland, far outside the range of present-day glaciers, led Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets had existed in now currently temperate areas

Why does had existed not work here? these ice sheets existed in the past...and Louis proposed this concept in the past. SO how come past past tense doesn't work?

A. in which great ice sheets had existed in now currently temperate areas.
B. in which great ice sheets existed in what are now temperate areas.
C. when great ice sheets existd where there were areas now temperate
D. when great ice sheets had existed in current temperate areas
E. when great ice sheets existed in areas now that are temperate

fangtray wrote:His studies of ice-polished rocks in his Alpine homeland, far outside the range of present-day glaciers, led Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets had existed in now currently temperate areas

Why does had existed not work here? these ice sheets existed in the past...and Louis proposed this concept in the past. SO how come past past tense doesn't work?

A. in which great ice sheets had existed in now currently temperate areas.
B. in which great ice sheets existed in what are now temperate areas.
C. when great ice sheets existed where there were areas now temperate
D. when great ice sheets had existed in current temperate areas
E. when great ice sheets existed in areas now that are temperate

IMO: B

whats the red mean? ..wrong? you cant' say when?

Use of past perfect is applicable when you are to refer two past events and that is not the case here so you can avoid had existed and GMAT always prefer simple tenses.

A - had existed is not necessary, now currently is redundant
C - where there were areas now temperate - change in tense, awkward and wrong
D - had existed - wrong again as in A.
E - temperate areas is preferable compared to areas now that are temperate - wrong

IMO B.

sam2304 wrote:Use of past perfect is applicable when you are to refer two past events and that is not the case here so you can avoid had existed and GMAT always prefer simple tenses.

A - had existed is not necessary, now currently is redundant
C - where there were areas now temperate - change in tense, awkward and wrong
D - had existed - wrong again as in A.
E - temperate areas is preferable compared to areas now that are temperate - wrong

IMO B.

i apologize ..i dont seem to understand.

why isnt there 2 past events though? 1837 is one time in the past.. and Louis proposed a concept of a time where it was even FURTHER in the past...it existed before 1837.

Past perfect is used to describe an action that occurred before another action in past. Emphasis is two actions - one occurring after the previous one has ended.
In this sentence only one action occurs, which is Louis proposing the concept of an age. 'in which' introduces age as a subject and describes it. Therefore simple past tense should be used instead of past perfect.
I hope this helps in clearing some ambiguity around usage of Past perfect.