To use past perfect both the events (VERBS) should be related. Here the verbs ''led'' and ''had existed'' are not related to each other. They both are independent.HIS STUDIES
led him to propose a concept has no bearing on existence
of ice sheets and vice versa.
The studies would have ''led'' his to a conclusion/concept even if the ice sheets did not exist. But, may be, the conclusion would have been a bit different one.
Please correct me if i am wrong.
The sentence doesn't have 4 clauses. It only has 2. A clause MUST contain SV pair.
Hope this helps.
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