The dry mountain ranges of the western United States contain rocks

Question

The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life. This rock record provides clues about one of the most significant radiations (periods when existing life-forms gave rise to variations that would eventually evolve into entirely new species) in the history of marine invertebrates. During this radiation the number of marine biological families increased greatly, and these families included species that would dominate the marine ecosystems of the area for the next 215 million years. Although the radiation spanned tens of millions of years, major changes in many species occurred during a geologically short time span within the radiation and, furthermore, appear to have occurred worldwide, suggesting that external events were major factors in the radiation. And , in fact, there is evidence of major ecological and geological changes during this period: the sea level dropped drastically and mountain ranges were formed, in this instance, rather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattern of habitats and nutrients, which in turn gave rise to the Ordovician radiation. However, the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood   1 
 1. The passage is primarily concerned with

(A) evaluating the evidence of a major geologic period and determining its duration 
(B) describing an evolutionary phenomenon and speculating about its cause 
(C) explaining the mechanisms through which marine life-forms evolved during a particular period 
(D) analyzing the impact on later life-forms of an important evolutionary development 
(E) contrasting a period of evolutionary change with other such periods

2 
 2. Which of the following can be inferred from the passage regarding the geologic changes that occurred during Ordovician period?

(A) They were more drastic than those associated with other radiations.
(B) They may have created conditions favorable to the evolution of many new life-forms.
(C) They may have caused the extinction of many of the marine species living in shallow waters.
(D) They may have been a factor in the development of new species adapted to living both on land and in water.
(E) They hastened the formation of the extensive dry regions found in the western united states.

3 
 3. Which of the following best describes the function of last sentence of the passage?

(A) it points out that the events described in the passage may be atypical.
(B) it alludes to the fact that there is disagreement in the scientific community over the importance of the Ordovician radiation.
(C) it concludes that the evidence presented in the passage is insufficient to support the proposed hypothesis because it comes from a limited geographic area.
(D) it warns the reader against seeing a connection between the biological and geologic changes described in the passage.
(E) it alerts the reader that current knowledge cannot completely explain the relationship suggested by the evidence presented in the passage.

Online test bank question number : RC00267-01 ~ RC00267-03

KarishmaB · Accepted Answer

Last sentence:
However, the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood.

The function of this sentence:

(D) it warns the reader against seeing a connection between the biological and geologic changes described in the passage.

The sentence does not warn against a connection. It warns that the connection isn't completely understood. The sentence does not say that there isn't a connection; it says that the connection isn't understood completely.

(E) it alerts the reader that current knowledge cannot completely explain the relationship suggested by the evidence presented in the passage.

Correct. It alerts that though the passage suggests evidence of the relation, the actual relation is not completely understood using the evidence.

P@PU · Answer

Kindly help to understand why Option C is not correct for Q1. The passage speaks about marine species which is specified in option C against option B,

arvind910619 · Answer

My friend,

Question 1 is "The passage is primarily concerned with". The meaning of the question stem is that you have to find the answer for which the passage was written.
So in question such as this general idea is the most important aspect. You have to read the whole passage and see what reason is it written for. So with this information in mind let us compare B and C

(B) describing an evolutionary phenomenon and speculating about its cause. 
This choice is our answer it tells us about the phenomenon and its cause. Radiation and various geological activities make are discussed deeply.

(C) explaining the mechanisms through which marine life-forms evolved during a particular period. 
Marine life is used as an example to the phenomenon of evolution during Ordovician period. So this can not be the aim of the passage.

saby1410 · Answer

VeritasKarishma   GMATNinja   GMATNinjaTwo 
Can you explain why option d of last question is incorrect

sssanskaar · Answer

In Question#2, can anyone explain why the correct answer is not E?

And , in fact, there is evidence of major ecological and geological changes during this period: the sea level dropped drastically and mountain ranges were formed, in this instance, rather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattern of habitats and nutrients, which in turn gave rise to the Ordovician radiation.

Option E states that "They hastened the formation of the extensive dry regions found in the western united states.".
I must say that I was torn between option B and E, but the highlighted portion made me incline towards option E.

Experts VeritasKarishma GMATNinja ? Your thoughts, please

Also, how to tackle such questions when these two options are so so close and seem indestructible.

KarishmaB · Answer

sssanskaar

The options are not close. There is a clear winner.

(B) They may have created conditions favorable to the evolution of many new life-forms.

these kinds of environmental changes may have resulted in an enriched pattern of habitats and nutrients, which in turn gave rise to the Ordovician radiation

So the passage mentions very clearly that these geologic changes may have resulted in more favourable conditions for new life forms.

(E) They hastened the formation of the extensive dry regions found in the western united states.

The geologic changes are 'sea level dropping' and 'mountains forming'. 'They' mentioned in this option are the geologic changes. How can mountain formation hasten the formation of dry regions? Mountain formation are the dry regions. 
The point is that these geologic changes provided various habitats and nutrients which gave rise to many new life forms.

Abhivas · Answer

The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life
I am confused in " dating back 440 to 510 million years , to the Ordovician period ".
Please explain me how this part is functioning grammatically. 
Thank you
  GMATNinja   GMATNinja Two  daagh  @mickemcgarry @e-GMAT  gmatwhiz

KarishmaB · Answer

"The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life."

Basic structure of the sentence - The ranges contain rocks

Modifiers for "rocks" -
- dating back 440 to 510 million years, to the Ordovician period,
- and teeming with evidence of tropical marine life

The rocks date back millions of years (440 million to 510 million). That was the Ordovician period. (the various periods of Earth's history are discussed here: https://en.wikipedia.org/wiki/Geologica ... y_of_Earth
Check out the Ordovician period)

The rocks are teeming with evidence of tropical marine life.

Abhivas · Answer

VeritasKarishma 
Thank you ma'am.
Still,I am confused how you linked date back million of years (440 to 510) to Ordovician period.

KarishmaB · Answer

... rocks dating back millions of years, to the Ordovician period, and teeming with ...

"to the Ordovician period" is a non essential prepositional phrase modifying "dating back", the present participle modifying "rocks"

We routinely use either of the two:

dates back millions of years 
or
dates back to the Ordovician period

Here, both are combined with "to the Ordovician period" acting as a non essential prepositional phrase.

makshay62 · Answer

Q2:

2. Which of the following can be inferred from the passage regarding the geologic changes that occurred during Ordovician period?

(A) They were more drastic than those associated with other radiations.
(B) They may have created conditions favorable to the evolution of many new life-forms.
(C) They may have caused the extinction of many of the marine species living in shallow waters.
(D) They may have been a factor in the development of new species adapted to living both on land and in water.
(E) They hastened the formation of the extensive dry regions found in the western united states.

Can anyone please help why (D) is wrong and (B) correct? based on which lines are the inferences being made?

GMATNinja · Answer

Question 2 
 
The passage tells us that " geological changes " during the Ordovician period "resulted in an enriched pattern of habitats and nutrients, which in turn gave rise to the Ordovician radiation."

Earlier in the passage, we learn that radiations are periods when "existing life-forms gave rise to variations that would eventually  evolve  into entirely new species." So, the  geological changes  during the Ordovician period led to enriched habitats, which in turn allowed entirely new species to  evolve .

Let's start with answer choice (D):

The passage supports the idea that the geological changes lead to the development of new species. However, it doesn't specify  what  these changes entailed. As a result, it doesn't support the idea that the new species were "adapted to  living on both land and water ." For all we know, the new species could have lived entirely in water, or entirely on land.

Since we just don't know, (D) is out.

Let's consider (B):

As discussed above, this statement is fully supported by the passage, so (B) is correct.

I hope that helps!

jarbit · Answer

Can someone help me to understand the question 1's answer? In the passage, author mentioned about evidence by mentioning, "And , in fact, there is  evidence  of major ecological and geological changes during this period". The answer (B) is describing an evolutionary phenomenon and speculating about its cause and it has speculation which is the complete opposite of evidence. What am I missing here?

GMATNinja · Answer

Question 1 
 
You're right that the author introduces some evidence in the passage, but to answer this question we're looking for the author's  primary  purpose. In other words,  why  did the author write this passage?

To answer these questions, first break down the structure of the passage as a whole. Here's an example of such a breakdown:

First, the author discusses some rocks that provide clues about a "radiation" of life-forms. 
 Then, the author suggests that "external factors" caused this radiation, and provides some evidence for this suggestion. 
 Finally, the author admits that the "actual relationship between these environmental factors and the diversification of life forms  is not yet fully understood. "

So, why did the author write this passage? From the above, we can tell that he/she wanted to discuss the reasons behind the radiation of life-forms. While the author does have one suggestion to explain the radiation, he/she also states that this issue is not yet fully understood.

This analysis fits nicely with option (B):
 
The author describes the radiation of life-forms and speculates that environmental factors might have caused it.

(B) is the correct answer to question 1.

I hope that helps!

KittyDoodles · Answer

Hi,

Please can you help explain what is wrong with option C, "explaining the mechanisms through which marine life-forms evolved during a particular period".

Will "the mechanisms through which marine life-forms evolved" be different from "the causes causing the phenomenon"? Wont causes be a part of the mechanism through which marine life-forms evolved?

Thanks

GMATNinja · Answer

Question 1 
 
The main issue with (C) for question 1 is the word "explaining." The author  doesn't actually know  what caused the radiation -- he/she just presents some  potential  factors. So, we can't say that the passage is primarily concerned with "explaining" the mechanisms through which marine life-forms evolved during a particular period.

(B) is a much better fit: the author describes the radiation, and then  speculates  about its cause.

I hope that helps!

Nikkz99 · Answer

I took 18:37 mins in total. I was taking down the points such that what does each statement mean as well as author's opinion. Alas! I got a perfect 0

{To be honest, I at least expected 2/3 to be correct... } The answers what I have chosen : Q1: C Reason , The question states about what does the passage mainly deals with. Since it talks about the Western US's rocks which dates back 440-510 M years ago to Ordovician Period, which suggests that there's evidence of marine life formation and further the passage talks about it. I opted option C. But, the official answer seems to be Option B, which states that the passages majorly talks about evolutionary phenomenon and speculating the case. Please help me with this case. Q2: A Question : "Which of the following can be inferred from the passage regarding the geologic changes that occurred during Ordovician period? " Reason why I have opted for option A is , {Although the radiation spanned tens of millions of years, major changes in many species occurred during a geologically short time span within the radiation and, furthermore, appear to have occurred worldwide, suggesting that external events were major factors in the radiation.} Which led to Ordovician period , right? Although option B too sounds favourable, But that's also a reason which helped in formation of Ordovician period, right? As the lines of passage states {ather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattern of habitats and nutrients, which in turn gave rise to the Ordovician radiation .} Isn't the question stressed on what happened during the Ordovician period but not what led to the Ordovician period ?? Q3: D The last sentence states the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood which means to say to the readers to be cautioned about the connection between biological (diversification of life forms) and geologic changes (environmental factors) , right? Why is option E was correct?! Skywalker18 , GMATNinja , bb , abhimahna , poojaarora1818 can anyone help me out? Thank You.

GMATNinja · Answer

Questions 1, 2, & 3 
 
Take another look at (B):

This one seems pretty air-tight. The passage describes the evolutionary phenomenon, "radiation." And phrases such as, "suggesting that external events were major factors in the radiation," speculate about the cause.

Now go back to (C):

Well, the last sentence of the passage is: "the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood." A relationship that isn't understood can't really be an explanation right?

In other words, the author is speculating about causes he doesn't understand, not explaining them. (C) is a classic "almost-but-not-quite" trap, and (B) is spot-on, so (B) wins for Q1.

Q2 
 
The problem with (A) is that we know nothing about other radiations, so there's no way to know if the Ordovician radiation is more drastic. Maybe they were all like this. (Or maybe they were even more extreme!)

And for (B) it sounds like you're confusing the Ordovician  period , a time frame during which many geological changes occurred, and the Ordovician  radiation , which is the evolutionary phenomenon that took place  during  the Ordovician period.

Put another way, the changes during the period led to the radiation. This is precisely what (B) is saying.

Q3 
 
Take a look at that last sentence again:

So we know there's some relationship between the environmental factors mentioned in the passage and evolution of all kinds of fun, new species, but we don't fully understand it.

That's basically what (E) says. If we don't full understand the relationship, seems fair to say that current knowledge cannot completely explain the relationship, right? So (E) is our answer. No need to overcomplicate it.

I hope that helps!

Rickooreoisb · Answer

Can someone explain by option C in question 3 is wrong

The dry mountain ranges of the western United States contain rocks

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The dry mountain ranges of the western United States contain rocks

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