Past Perfect vs. Present Perfect

Question

I am a new member on this site. So please guide me somewhere else if I post anything incorrect.

I have been working on these two sentence corrections that ask about Present Perfect, Past Perfect and the Simple Past. They have been a little confusing.

During the 1950s, the Detroit area emerges as a metropolitan region with the construction of an extensive freeway system that had expanded in ensuing decades.

For the one above, I said had expanded should be changed to has expanded since this is continuing to happen (ensuing decades).

However the answer is supposed to be expanded.

In a discovery at least fifty yeas in the making, a new and bizarre dinosaur species has been identified in a slab of rock collected by scientists working in South Africa in the 1960s.

The answer I put for this one is was since this happened in the past.

However the book says that it is fine as it is.

Although the ancient Egyptians abandoned Demotic more than 1,500 years ago, taking up Coptic and eventually Arabic, the language lived on in words like "adobe," which entered Spanish before passing into English.

For the one above I said has lived should be the accurate answer since the language is still living on in English...

However the answer is to leave it as it is.

I would appreciate if you guys could provide a different perspective into this.

Answer 1

There are three sentences in which the interaction of tenses, is being examined for error:

1. During the 1950s, the Detroit area emerges as a metropolitan region with the construction of an extensive freeway system that had
   expanded in ensuing decades.

2. In a discovery at least fifty years in the making, a new and bizarre dinosaur species has been identified in a slab of rock collected by scientists working in South Africa in the 1960s.

3. Although the ancient Egyptians abandoned Demotic more than 1,500 years ago, taking up Coptic and eventually Arabic, the language lived on in words like "adobe," which entered Spanish before passing into English.

The first is the only sentence containing a tense error. The fronted prepositional phrase During the 1950s suggests a historical present interpretation of emerges. It might have been clearer as emerged, but the actual time remains past regardless. The relative pronoun that suggests expand, the verb of the relative clause, should express a tense relative to the past time of the main verb emerge. The past perfect erroneously suggests the activity of expanding happened before the activity of emerging, which the context of ensuing decades prohibits.

In a historical perspective, has expanded, the present perfect, is not an optimal choice. Although it does not contradict the relative historical context created by ensuing decades, it does introduce ambiguity about the activity of expanding--plausibly extending it all the way to the present, which is not the intent of the historical narrative.

The past tense expanded is a better choice. It clearly places the activity of expanding in the past from the reader's perspective, but it doesn't contradict the relative context of ensuing decades in the historical perspective.

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Since the other two sentences contained no errors, they do not need to be corrected.

In the second sentence, the main verb is has been identified. The present perfect tense is particularly useful for the ongoing present state of identification as the result of past identifying work. The expression, [which was] collected by scientists working in South Africa in the 1960s. is a reduced relative clause, and the past tense accurately puts the activity of collecting before the present state of identification.

In the third sentence, the present perfect expression has lived on would be just as acceptable as the past expression lived on, but it is not superior. The verb lived on contains a semantic element of progressive action which expresses the perfect aspect sufficiently.