Even though this is an old thread, I hope to get an answer for this OG problem, #70.
Why the bold text " ice sheets existed in what are now temperate areas" is correct?
Are these bold expressions correct?
" ice sheets had existed in now..."
" ice sheets existed where there were..."
" ice sheets had existed in current temperate..."
" ice sheets existed in areas ..."
Regarding the usage of "in which" and "when", they can be used interchangeably. According to MGMAT SC "the pronoun when can be used to modify a noun event or time, such as period, age, 1987, or decade. In these circumstance, you can also use in which instead of when. So, whenever we see time or event nouns, we can use either when or in which.
I believe that the usage of in which for place nouns is different than the one presented above. Where can be used to modify a noun place ( a physical one) and in which can modify a "situation, condition, case, circumstances, or arrangements"- MGMAT SC.
So, I look forward to your explanation for the questions above.
Thanks.