A newly released study on the tectonic plates forming the Pacific basi

A newly released study on the tectonic plates forming the Pacific basin indicates that by the time they had shifted even a few miles, a vast percentage of the coastline which is currently home to major world cities, because of global warming, will have already become entirely submerged.

Concepts to look for: Verb tense, idiom, pronoun reference, word order, altered intent and change of meaning

1. by the time they had shifted even a few miles, a vast percentage of the coastline which is currently home to major world cities, because of global warming, will have already become entirely submerged --- 'had shifted' is a tense error.


2. by the time they shift even a few miles, a vast percentage of the coastline, which is currently a home of the major world cities, will have already become entirely submerged due to global warming --- 'home of' is idiom error

3. by the time they have shifted even a few miles, a vast percentage of the coastline currently home to major world cities already will have become entirely submerged because of global warming -- avoids the tense, idiom and altered intent pitfalls.

4. a vast percentage of the coastline that is currently home to major world cities will have already become entirely submerged due to global warming by the time they have shifted even a few miles-- altered intent due to wrong word order. The choice suggests that the cities have shifted a few miles rather than the plates have.

5. a vast percentage of the coastline that is currently home to major world cities, by the time the plates have shifted even a few miles, will become entirely submerged because of global warming ---- Altered intent due to wrong word orders. The choice says that the plates will have submerged rather than the cities will have.
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Use of future perfect is necessary in this case.

First consider the use of past perfect: When there are references of two interrelated past events (verbs or time references), then the former event should be in past perfect.

By year 2000, I had completed my studies.... correct. (past perfect)
By year 2000, I completed my studies... wrong. (simple past)
In year 1999, I completed my studies.... correct. (simple past)

(Here note that the latter event may not necessarily be a verb and can merely be a time reference , e.g. year 2000 in the above example).

Now with the above idea in mind, examine option E.
By year 2075, the coastline will have become submerged.. correct (future perfect)
By year 2075, the coastline will become submerged.... wrong. (simple future).
In year 2074, the coastline will become submerged.. correct (simple future).

Now you would see why simple future in option E is wrong and future perfect in option C is correct.

What does 'already' modify in OA in presence of 'currently'? Usage of both 'already' and 'currently' here seems unusual.
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How do we know that they refers to the tectonic plates?

'Currently' refers to the shore that is at the moment a land area much above the sea level. having big coastal cities. But when the plates eventually start drifting and have moved even a few miles apart, the consequential displaced waters of the sea would have pushed these cities to the bottom.
These are hypothetical eventualities.
Look at a similar sentence:
Although I am already in deep debts just now as a farmer, I will have cleared all of them fully when the government will have waived all the agricultural loans a little before the next general elections.
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deepachr
If 'they' did not refer to the plates, what else is the other eligible plural noun in the sentence?. None; therefore, plates is the correct antecedent.
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Thanks Sir.

Would you please say something about the usage of 'already' along with 'will' in a same sentence? Already indicates past events where 'will' indicates future events. Am I correct?
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Mahmud6, it's not necessarily a problem to mix the past with the future on the GMAT, regardless of whether we're talking about verb tenses, "time markers" such as "already", or a combination of both. It's completely natural to compare the past, present, and future in a single sentence, and it's something we do regularly in normal speech:

Souvik studied hard for his GMAT, but I am a lazy person and therefore will not study for any standardized test.

No worries, right? We're using three different verb tenses, but since it makes sense with the meaning of the sentence, it's not an issue. Fundamentally, when the GMAT uses different tenses, they're just asking you to verify that the mix of tenses actually matches the intended meaning. So there really aren't many relevant rules that forbid the mixing of verb tenses in a single sentence.

And we could stick the word "already" in there, and the same ideas would apply:

Souvik already spent 500 hours studying for his first attempt at the GMAT, so he will not study much for his second attempt.

I hope this helps!
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1. already need not mean the past. If you say you are already good at Quants today, it does not mean you were good only in the past and not good in the present or in the future.

In the given case, already is in the subordinate clause and the will is in the main clause. Therefore, both are in two different settings.
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May be I have got the point. 'Already' is modifying currently home NOT the submerge. I slightly modify the sentence as below to get the meaning.

, a vast percentage of the coastline already currently home to major world cities will have become entirely submerged because of global warming

Am I Correct?
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Mahmud wrote


mahmud

1. Neither currently nor already is modifying 'submerged"; if they are either currently or already submerged, then it doesn't mean much to say that they will have become submerged in the future once again.

2. 'Already and currently' are both adverbs and therefore, they cannot modify each other nor can they be placed back to back when they essentially belong to two different sentences.
3. then, what are the verbs modified by each of these adverbs.

Here if you expand the first part of the sentence a little, it will mean that a vast percentage of the coastline that is currently home to major world cities; So currently actually modifies the verb 'is' which is understood.
'Already' in the second part modifies the verb 'will have become'.
I appreciate that this is a tricky modification issue in a complicated setting
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Hi sir,
It may seem silly question. Sorry for troubling you.
If in B "home of" were to become "home to", would the sentence be correct ?
thank you.

No question is silly! If you're wondering about something, I can promise that somebody else is, too. So please don't be shy!

Even if you switched "the home of" to "home to", there would still be a problem in (B): "due to" phrases can only modify nouns, not verbs. In this case, "due to global warming" logically modifies "submerged", so it's wrong.

I hope this helps!
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Isn't C a run on??
The answer should be E, right?

Please explain each and every option in detail.

(C) definitely isn't a run-on. By definition, a run-on sentence consists of two independent clauses that aren't appropriately separated by punctuation or a conjunction.

In (C), the sentence begins with an independent clause: "A newly released study on the tectonic plates forming the Pacific basin indicates..." The rest of the sentence is a subordinate clause, beginning with the word "that": "...that by the time they have shifted even a few miles, a vast percentage of the coastline currently home to major world cities already will have become entirely submerged because of global warming."

So grammatically speaking, this is completely fine: just an independent clause with a long subordinate clause.

Check out the excellent explanations by daagh and akshayk above. If you still have specific questions after that, let us know!
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I may be stupid to understand this issue. I beg your pardon.

According to google search the term 'already' means 'before or by now or the time in question'. From this we may deduce that already can not modify future event.

'Will have become' is a future event. So, how can already modify 'Will have become'?
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Mahmud6, check out the last part of that definition: "or the time in question." The word "already" means that something has happened by whatever time we are talking about. So if that time is in the future, it just has to have happened before that future point.

Examples:
By the time I finish reading this book, the sequel will already have come out.
By the time the sun goes supernova, you and I will already be gone.
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A newly released study on the tectonic plates forming the Pacific basin indicates that by the time they had shifted even a few miles, a vast percentage of the coastline which is currently home to major world cities, because of global warming, will have already become entirely submerged.

1. by the time they had shifted even a few miles, a vast percentage of the coastline which is currently home to major world cities, because of global warming, will have already become entirely submerged -"had" is wrongly used. A comma is required before which.
2. by the time they shift even a few miles, a vast percentage of the coastline, which is currently a home of the major world cities, will have already become entirely submerged due to global warming -due to is wrongly used.
3. by the time they have shifted even a few miles, a vast percentage of the coastline currently home to major world cities already will have become entirely submerged because of global warming -Correct
4. a vast percentage of the coastline that is currently home to major world cities will have already become entirely submerged due to global warming by the time they have shifted even a few miles -"they" is misplaced pronoun. It might refer back to either cities or plates.
5. a vast percentage of the coastline that is currently home to major world cities, by the time the plates have shifted even a few miles, will become entirely submerged because of global warming -meaning change. information regarding "plates" appears to be unnecessary.

Hi GmatNinja,
Sorry for troubling you. I will be obliged if you can help me to understand why option E is wrong. I got why option C is correct, but is having a difficulty to eliminate option E.
E) a vast percentage of the coastline that is currently home to major world cities, by the time the plates have shifted even a few miles, will become entirely submerged because of global warming
here cities will become submerged and not plates as, by the time the plates have shifted even a few miles, are set of by commas, so this looks like non-essential modifier. now, the plates will modify the previous clause- a vast percentage of the coastline that is currently home to major world cities. Plates cant modify the next clause- will become entirely submerged because of global warming because then the clause a vast percentage of the coastline that is currently home to major world cities will modify what? both plates and cities cant modify the same thing- will become entirely submerged because of global warming.
The only reason I find option E to eliminate is that by the time the plates have shifted even a few miles needs to be part of the main sentence and not as a non-essential modifier.
Please help.