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The basic theory of plate tectonics recognizes two ways

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The basic theory of plate tectonics recognizes two ways  [#permalink]

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Updated on: 26 Sep 2017, 07:49
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Continental Margins

The basic theory of plate tectonics recognizes two ways continental margins can grow seaward. Where two plates move away from a midocean rift that separates them, the continental margins on those plates are said to be passive. Such continental margins grow slowly from the accumulation of riverborne sediments and of the carbonate skeletons of marine organisms. Since most sequences of such accretions, or miogeoclinal deposits, are unreformed, passive margins are not associated with mountain building.

Along active margins continents tend to grow much faster. At an active margin an oceanic plate plunges under a continental plate, fragments of which then adhere to the continental margin. The process is met with extensive volcanism and mountain building. A classic example is the Andes of the west coast of South America.

In the original plate-tectonic model western North America was described as being initially passive and then active. It was assumed that the continent grew to a limited extent along this margin as oceanic rocks accreted in places such as the Coast Ranges of California. The model was successful in explaining such disparate features as the Franciscan rocks of the California Coast Ranges, created by subduction, and the granite rocks of the Sierra Nevada that originated in volcanoes.

The basic plate-tectonic reconstruction of the geologic history of western North America remains unchanged in the light of microplate tectonics, but the details are radically changed. It is now clear that much more crust was added to North America in the Mesozoic era than can be accounted for by volcanism and by the simple accretion of sediments. Further, some adjacent terranes are not genetically related, as would be expected from simple plate tectonics, but have almost certainly travelled great distances from entirely different parts of the world.

1. Which one of the following best expresses the main idea of the passage?

(A) The margin of the west coast of North America developed through a combination of active and passive mechanisms.
(B) The growth of continental margins is only partially explained by the basic theory of plate tectonics.
(C) Continental margins can grow seaward in two ways, through sedimentation or volcanism.
(D) The introduction of microplate tectonics poses a fundamental challenge to the existing theory of how continental margins are formed.
(E) Continental margins grow more rapidly along active margins than along passive margins.

2. The passage supplies information for answering all of the following questions regarding continental margins EXCEPT:

(A) How have marine organisms contributed to the formation of passive continental margins?
(B) What were some of the processes by which the continental margin of the west coast of North America was formed?
(C) Are miogeoclinal deposits associated with mountain building along continental margins?
(D) How was the continental margin of the west coast of South America formed?
(E) How much crust added to North America in the Mesozoic era can be accounted for by the accretion of sediments from the ocean floor?

3. The author mentions the Franciscan rocks of the California Coast Ranges in order to make which one of the following points?

(A) The basic theory of plate tectonics accounts for a wide variety of geologic features.
(B) The original plate tectonic model falls short of explaining such features.
(C) Subduction processes are responsible for the majority of the geologic features found along the west coast of North America.
(D) Passive margins can take on many geologic forms.
(E) The concept of microplate tectonics was first introduced to account for such phenomena.

4. Which one of the following does the author mention as evidence for the inadequacy of the original plate tectonic model to describe the formation of continental margins?

(A) Nearly flat, unreformed crystal blocks have been found along some continental margins where there are mountains further inland.
(B) Sediments and fragments from the depths of the ocean accumulate along continental margins.
(C) Large pieces of the Earth's crust that appear to be completely unrelated are found in the same area today.
(D) Unreformed miogeoclinal deposits are usually not linked to mountain building.
(E) Oceanic plates drop beneath continental plates along active margins.

Originally posted by Nikkb on 26 Sep 2017, 03:51.
Last edited by broall on 26 Sep 2017, 07:49, edited 1 time in total.
Reformatted question
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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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12 Sep 2018, 22:43
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+1 kudos to the posts containing answer explanations of all questions

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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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12 Sep 2018, 23:06
Can anyone help with Question no. 4?

Please give evidences from the passage as well..

Thanks
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13 Sep 2018, 00:34
not sure of the ans for Q4.
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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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13 Sep 2018, 09:05
3
Q1.
A- Partially correct(only final para deals with this).
C- Because its passive/active.
D- The passage does not mention any challenge. It indeed supports the traditional theories.
E- Out of scope.

Q2.
A - It is covered. Such continental margins grow slowly from the accumulation of riverborne sediments and of the carbonate skeletons of marine organisms.
C- Last line para 1. Since most sequences of such accretions, or miogeoclinal deposits, are unreformed, passive margins are not associated with mountain building.
D- A classic example is the Andes of the west coast of South America.

Q3.
B- The model was successful in explaining such disparate features. So wrong.
C- Subduction is for one feature. Not main point.
D- It had both active and passive.
E- Out of scope, it is not first.

Q4.
Last para:
It is now clear that much more crust was added to North America in the Mesozoic era than can be accounted for by volcanism and by the simple accretion of sediments. Further, some adjacent terranes are not genetically related, as would be expected from simple plate tectonics.
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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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13 Sep 2018, 09:58
Holy Lord.....9:15 for the entire passage.All correct.

So question 4 is basically asking "What is wrong with the original theory and what does the author give us as proof that it is wrong...?".

As with all RC's(especially when we have all 5 options) find the right answer instead of eliminating the wrong answers.

"Problem with the original theory" is touched upon only in the 4th Para.So go to the 4th para.

the 2nd sentence = " More crust was added than expected by the original theory(active+passive)"
Also 3rd sentence = "Rocks not related(genetically) were also found"

If you read the options you will quite clearly notice that C is a restatement of these 2 sentences.

Any other help with this passage...?
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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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13 Sep 2018, 10:13
rahulkashyap wrote:
not sure of the ans for Q4.

Further, some adjacent terranes are not genetically related, as would be expected from simple plate tectonics, but have almost certainly travelled great distances from entirely different parts of the world.

There is dissimilarity in the two terrains in spite of being present in the same area.
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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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13 Sep 2018, 13:19
1
Please update the source to "Kaplan 800".
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14 Sep 2018, 00:27
rahulkashyap wrote:
not sure of the ans for Q4.

rahulkashyap,

the clue for the answer lies in the last lines of the passage -"Further, some adjacent terranes are not genetically related, as would be expected from simple plate tectonics, but have almost certainly travelled great distances from entirely different parts of the world."

Genetically not related refers to the geographical anomaly of having a piece of crust unrelated to its surroundings and "as would be expected from simple plate tectonics" refers to the inadequacy of the model.

Hope this helps..and if it does, please hit Kudos. workout, await your inputs.
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The basic theory of plate tectonics recognizes two ways  [#permalink]

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24 Sep 2018, 07:44
2
Notes:
1) Theory intro.
-2 ways margins grow
-passive

2) Active margins are faster

3) Model and stuff it explains
- model; NA - passive to active

4) Stuff model doesn't explain
-more crust

Prethinking: A theory is talked about and it is implied it doesn't completely explain stuff --> B wins

1. Which one of the following best expresses the main idea of the passage?

(A) The margin of the west coast of North America developed through a combination of active and passive mechanisms. very partial scope
(B) The growth of continental margins is only partially explained by the basic theory of plate tectonics. --> prethought
(C) Continental margins can grow seaward in two ways, through sedimentation or volcanism. -- partial scope
(D) The introduction of microplate tectonics poses a fundamental challenge to the existing theory of how continental margins are formed.
(E) Continental margins grow more rapidly along active margins than along passive margins. --> this is not the main idea though.. partial scope

Can anyone help with Q2 in detail? I couldn't choose b/w A and E. I chose A because of the quoted text below:

2. The passage supplies information for answering all of the following questions regarding continental margins EXCEPT:
B, C, D are eliminated easily

(A) How have marine organisms contributed to the formation of passive continental margins?
Where two plates move away from a midocean rift that separates them, the continental margins on those plates are said to be passive. Such continental margins grow slowly from the accumulation of riverborne sediments and of the carbonate skeletons of marine organisms.

(B) What were some of the processes by which the continental margin of the west coast of North America was formed?
(C) Are miogeoclinal deposits associated with mountain building along continental margins?
(D) How was the continental margin of the west coast of South America formed?

(E) How much crust added to North America in the Mesozoic era can be accounted for by the accretion of sediments from the ocean floor?
It is now clear that much more crust was added to North America in the Mesozoic era than can be accounted for by volcanism and by the simple accretion of sediments.
Clearly, we don't know how much crust was added. The passage literally says that. E wins.

4. Which one of the following does the author mention as evidence for the inadequacy of the original plate tectonic model to describe the formation of continental margins?
author talks about model not always explaining stuff in last para. let's go there and quickly rescan it.

The basic plate-tectonic reconstruction of the geologic history of western North America remains unchanged in the light of microplate tectonics, but the details are radically changed. It is now clear that much more crust was added to North America in the Mesozoic era than can be accounted for by volcanism and by the simple accretion of sediments. Further, some adjacent terranes are not genetically related, as would be expected from simple plate tectonics, but have almost certainly travelled great distances from entirely different parts of the world.

(A) Nearly flat, unreformed crystal blocks have been found along some continental margins where there are mountains further inland.
(B) Sediments and fragments from the depths of the ocean accumulate along continental margins.
(C) Large pieces of the Earth's crust that appear to be completely unrelated are found in the same area today. -->rewording of highlighted part
(D) Unreformed miogeoclinal deposits are usually not linked to mountain building.
(E) Oceanic plates drop beneath continental plates along active margins.

C wins
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Re: The basic theory of plate tectonics recognizes two ways  [#permalink]

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04 Oct 2018, 11:58

TIA
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08 Oct 2018, 19:43
workout could you explain this passage as a whole please??
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The basic theory of plate tectonics recognizes two ways  [#permalink]

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Updated on: 22 Oct 2018, 07:03
1
Hey guys please find below the answers and explanations of the respective passageMG1105 ShankSouljaBoi rahulkashyap hongg7 workout

1.В, 2.E, 3.A, 4.С

1.

(В) First up is a main idea question. While the basic theory of plate tectonics explains much about the growth of continental margins, the fourth paragraph suggests that it cannot fully explain certain geologic details.
(B) captures this, and is the correct answer. An 800 test taker stays alert throughout the entire passage since the author's full main idea may not emerge until the end.
(A) and (E) both represent true statements, but they're details from the passage, not the passage's main idea. An 800 test taker can distinguish betwttn the main idea if a pfssage and facts that are merely reflected in the pfssage. (C) distorts the notion of the two ways that continental margins can grow. Though the first paragraph mentions sedimentation as an example of passive margins, and paragraph 2 states that volcanism often results from active margin growth, the author never goes so far as to say that sedimentation and volcanism are the two ways that continental margins grow. And even if this could be inferred, it's still not big enough to be the main point of the passage.
(D) is incorrect because the first sentence of paragraph 4 states that the basic plate tectonic theory remains unchanged in the light of microplate tectonics; it's the details that are radically changed, not the basic theory.

2.

(E) This is an unusually worded detail question, but it does force us to focus on the details nonetheless. The question in each wrong choice is one that can be answered by the information in the passage, while the right answer is one that goes unanswered by the author. Let's check the choices.
(A) is covered in the first paragraph, which describes the growth of passive margins. There, the author says that passive margins grow, in part, through the accumulation of the carbonate skeletons of marine organisms.
(B) is the subject of the paragraph 3—the continental margin of the west coast of North America grew at first as a passive margin, and then as an active margin.
(C) is answered in the last sentence of paragraph 1: miogeoclinal deposits are associated with passive margins and are "generally not associated with mountain building."
(D) We have to search a bit for the answer to the question posed in choice (D): the last sentence of the second paragraph says that the west coast of South America is an active margin.
(E) That leaves (E), which must be correct. In fact, if you had full confidence eliminating the other four choices, you could choose (E) without much fanfare and move on. An 800 test taker has confidence in her work, and uses that confidence to save time whenever possible. Indeed, the question in (E) cannot be answered by information contained in the passage. Microplate tectonics has revealed that much more crust was added to North America in the Mesozoic period than was added from volcanism and the accretion of sediments, but that doesn't tell us precisely how much crust the accretion of sediments accounts for in the grand scheme of things.

3.

(A) The Coast Ranges of California are introduced in paragraph 3 to provide an example of the variety of geologic features that the original plate-tectonic model could successfully explain: the Franciscan Rocks, formed by local subduction, and the granite rocks of the Sierra Nevada, formed by volcanic action.
(A) therefore represents the best account of why this detail was mentioned. (B) is wrong because the problems with the basic plate tectonic model are discussed in paragraph 4, a paragraph in which the California Coast Ranges are never mentioned.
An 800 test taker remains conscious of where in the passage certain ideas are presented, and uses that knowledge to help eliminate choices that deal with material far from the issue in question.
(C) is a distortion of the facts. We don't know if subduction processes are responsible for the majority of the west coast's geologic features—we're told only that they are responsible for some, such as the Coast Ranges.
(D) is wrong because the Coast Ranges were formed by local subduction processes, according to paragraph 3, not by the actions of passive margins. (E) The concept of microplate tectonics was introduced to account for phenomena that the basic, or original, plate-tectonic model could not adequately explain. But the Coast Ranges are features that the basic model can account for, so (E) is incorrect.

4.

(C) The inadequacy of the plate tectonic model is introduced in the final paragraph of the passage. There we're told that genetically distinct pieces of the Earth's crust are found in the same area, a fact which the original plate tectonic model cannot explain.
(C) gets at this issue.
(A) The original plate tectonic model can account for (A)—see the third and fourth paragraphs.
(B), (D), and (E) are true statements—see the first and second paragraphs—but none of these statements has a direct bearing on the issue of the inadequacy of the original plate tectonic model.

An 800 test taker is not tempted by a choice simply because it contains a true statement. It must, first and foremost, answer the question that was asked.
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Originally posted by GmatWizard on 22 Oct 2018, 04:54.
Last edited by workout on 22 Oct 2018, 07:03, edited 1 time in total.
Removed spoiler tag since this RC was posted a while ago and there were explanations above already.
The basic theory of plate tectonics recognizes two ways   [#permalink] 22 Oct 2018, 04:54
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