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An extinction event also known as a mass extinction or biotic crisis

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An extinction event also known as a mass extinction or biotic crisis [#permalink]

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An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the amount of life on earth. Such an event is identified by a sharp change in the diversity and abundance of macroscopic life. It occurs when the rate of extinction increases with respect to the rate of speciation. Because the majority of diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life.

Over 98% of documented species are now extinct, but extinction occurs at a very uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organism fossils.

Since life began on Earth, the five major mass extinctions have significantly exceeded the background extinction rate for animal and plant species. The most recent, the Cretaceous–Paleocene extinction event, which occurred approximately 66 million years ago, was a large-scale mass extinction of animal and plant species in a geologically short period of time. In the past 540 million years, during each of these five major events, over 50% of animal and plant species died. Mass extinctions seem to be a Phanerozoic-era phenomenon, with extinction rates low before large complex organisms arose.

(1) It can be inferred from the passage that:

(A) in an extinction event, there is a dramatic decrease in microbial life on earth.
(B) over 90% of easily observed, biologically complex species become extinct during a biotic crisis.
(C) the background extinction rate of animal and plant species is well below 50%.
(D) marine fossils are easier to find and thus more useful to those studying mass extinction events.
(E) new species do not emerge during a mass extinction event.
[Reveal] Spoiler:
C



(2) It can be inferred from the passage that the Phanerozoic era was:

(A) a time period that existed before 540 million years ago.
(B) a time period during which few new species emerged.
(C) a time period before the Cretaceous–Paleocene era.
(D) a time period during which large, complex organisms existed.
(E) a time period during which fewer than 50% of animal and plant species died.
[Reveal] Spoiler:
D



(3) The author would most probably agree with which of the following statements?

(A) The diversity of microbial life has changed dramatically during mass extinction events.
(B) The Cretaceous–Paleocene extinction event was the most significant in the past 540 million years.
(C) There were many mass extinction events prior to 540 million years ago.
(D) Extinction rates have varied widely over the past 540 million years.
(E) Mass extinctions are less likely now than in the past 540 million years.
[Reveal] Spoiler:
D



(4) The primary purpose of the passage is to:

(A) warn readers about the possible dangers of mass extinction events.
(B) discuss the causes of a particular scientific phenomenon.
(C) present new evidence to support the theory of mass extinction events.
(D) describe an important scientific and historical occurrence
(E) suggest that mass extinctions are likely to continue in the future.
[Reveal] Spoiler:
D

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA

Last edited by broall on 03 Sep 2017, 05:12, edited 1 time in total.
Reformatted question

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Re: An extinction event also known as a mass extinction or biotic crisis [#permalink]

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New post 30 Apr 2015, 21:21
most, if not all gmat passage, are well structured and hard to understand , followed by easy question testing the understanding of the passages. this case is opposite to the case created by prep companies, in which passages are too easy, and not well structured and followed by very hard questions.

gmat test us ability to understand the passages and to infer from information in the passage. I think prep companies' passages test only the inference.

I alway see that the gmat typical passages are harder than the prep companies tests.
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Re: An extinction event also known as a mass extinction or biotic crisis [#permalink]

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New post 30 Apr 2015, 23:15
DAMN!!! questions blew me off!!
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Re: An extinction event also known as a mass extinction or biotic crisis [#permalink]

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New post 18 Jul 2015, 00:03
Can someone provide an explanation for Q2?

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Re: An extinction event also known as a mass extinction or biotic crisis [#permalink]

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New post 29 Jul 2015, 09:40
Damn..... I did it all right!

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Re: An extinction event also known as a mass extinction or biotic crisis [#permalink]

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New post 02 Aug 2015, 12:51
if nybody can explain me q3...also other oe..

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Re: An extinction event also known as a mass extinction or biotic crisis [#permalink]

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New post 03 Sep 2017, 05:14
OE from Veritas:

[Reveal] Spoiler: Question 1
In this example, as is the case with many hard inference problems, you must link several pieces of information to find the proper inference. Using process of elimination, start with (A). In the first paragraph you learn that mass extinction events are based on the extinctions of easily observed, biologically complex components. You therefore have no idea from this passage how the microbial organisms are affected during a mass extinction event and (A) is incorrect. In the passage you learn that 98% of known species have become extinct but you only learn that over 50% were lost in each of the 5 major mass extinctions. You therefore cannot conclude that over 90% of complex species become extinct during a mass extinction event and (B) is also incorrect. Note: the testmakers are hoping you use the wrong data point to create this improper inference. (C), which is correct, requires that you link together two pieces of information. In the beginning of the 3rd paragraph you learn that “the five major mass extinctions have significantly exceeded the background extinction rate” and then you learn that the rate of those mass extinctions is well over 50%. This allows you to conclude that the background rate is far below 50%. In (D), you learn that marine fossils are used because they provide a better fossil record and stratification but you do not know if they are easier or more difficult to find than other types. In (E), no information is given about whether new species emerge during an extinction event so you cannot make that inference. Answer is (C).


[Reveal] Spoiler: Question 2
For this type of question, go find the key word (end of the last paragraph) and make the proper inference. The sentence reads: “Mass extinctions seem to be a Phanerozoic-era phenomenon, with extinction rates low before large complex organisms arose.” In the first part of the sentence you learn that mass extinctions took place during this era. In the second part you learn that the extinction rates were low before “large complex organisms arose” (i.e. before this era.) From this you can conclude definitively that this era was a time during which large, complex organisms existed and (D) is thus correct. (A) must be false from this information, as the Phanerozoic era had to overlap with those 540 million years. For (B), you have no idea from this passage about the emergence of species. Again, (C) is contradicted by this section and for (E) you cannot make this inference (and the passage suggests that number is near 98%). Answer is (D).


[Reveal] Spoiler: Question 3
As you learned in several previous questions, you cannot assess the impacts on microbial life from this passage so (A) is incorrect (you have no idea what the author would think). For (B), while the author references this extinction event specifically, no information is given about its significance in relation to the other major extinction events. (C) is contradicted by the passage as you learn at the end of the passage that extinction rates were low before that time period. For (D), there is direct support for this statement in the first sentence of the 2nd paragraph, in which the author states that “extinction occurs at a very uneven rate.” No information is given in the passage to support (E) so it is incorrect. Answer is (D).


[Reveal] Spoiler: Question 4
For primary purpose questions, you should focus on the scope of the passage and the intent of the author. For (A) the author does not give any specific warnings and the passage is explanatory/descriptive, not opinionated. For (B), the author does not discuss at all what has caused these mass extinction events. He simply discusses what they are and when some have occurred. For (C), the author does not present any new evidence, just discusses what is known about them now. (D) matches the scope and tone perfectly and is thus correct. For (E) there is no discussion about what will occur in the future. Answer is (D).

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Re: An extinction event also known as a mass extinction or biotic crisis   [#permalink] 03 Sep 2017, 05:14
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An extinction event also known as a mass extinction or biotic crisis

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