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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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New post Updated on: 28 Feb 2018, 04:45
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Coding for RC
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.
Q1: 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.

OA : c


Q2 : 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.

OA : d


Q3: 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.

OA : d


Q4: 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.

OA : d


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Originally posted by aashu4uiit on 29 Oct 2014, 12:30.
Last edited by Skywalker18 on 28 Feb 2018, 04:45, edited 1 time in total.
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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 Jan 2017, 05:53
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kavish2000 wrote:
For the Q-3, can you please explain as to how can we conclude the same about Phanerozoic era?

The passage mentions that Mass Extinctions were Phanerozoic era phenomenon with rates low before large organisms arose. Should not this sentence structure mean that phanero era was the one wherein the extinction rates were low and was the era devoid of large organisms?


Your misunderstanding of the last line of the passage seems to be a result of not being able to inerpret the function of the modifier "with extinction rates low before large complex organisms arose" properly. This modifier does not refer to "Phanerozoic-era phenomenon", but the entire previous clause. Shift the modifier at the beginning, and then probably the meaning would be clear:

With extinction rates low before large complex organisms arose, mass extinctions seem to be a Phanerozoic-era phenomenon.

The above sentence implies that extinction rates were low before large complex organisms arose. This also implies that mass extinctions were possible only AFTER large complex organisms arose. Since mass extinctions occured during the Phanerozoic-era, it can be inferred that there were large complex organisms during this era. Hence D is the correct option.
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Re: An extinction event (also known as a mass extinction or biotic crisis)  [#permalink]

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New post 21 Mar 2016, 23:55
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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.

Q1: It can be inferred from the passage that:
a) in an extinction event, there is a dramatic decrease in microbial life on earth................only macroscopic life can be observed and we have no proper measured info reg microbial life
b) over 90% of easily observed, biologically complex species become extinct during a biotic crisis...........it is not a norm which happens all the time
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.Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic but whether they are easy to find is not known as per the passage.
e) new species do not emerge during a mass extinction event..............new info since nowhere it is mentioned about species emerging activity.

Q2 : 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.only macroscopic life can be observed and we have no proper measured info reg microbial life
b) The Cretaceous–Paleocene extinction event was the most significant in the past 540 million years..............recent major event that happenend in short time. We dont know whether it is most significant or not.
c) There were many mass extinction events prior to 540 million years ago...........Since life began on Earth, and In the past 540 million years, during each of these five major events, does not give any info of mass events before 540 million yrs
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..........there is no such prediction.


Q4: The primary purpose of the passage is to:

a) warn readers about the possible dangers of mass extinction events...........author did not warn anyone
b ) discuss the causes of a particular scientific phenomenon............author did say It occurs when but did not say why
c) present new evidence to support the theory of mass extinction events.......there is mention of new evidence
d) describe an important scientific and historical occurrence
e) suggest that mass extinctions are likely to continue in the future........there is mention of suggestion
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Re: An extinction event (also known as a mass extinction or biotic crisis)  [#permalink]

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New post 11 Jan 2017, 19:21
For the Q-3, can you please explain as to how can we conclude the same about Phanerozoic era?

The passage mentions that Mass Extinctions were Phanerozoic era phenomenon with rates low before large organisms arose. Should not this sentence structure mean that phanero era was the one wherein the extinction rates were low and was the era devoid of large organisms?
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Re: An extinction event (also known as a mass extinction or biotic crisis)  [#permalink]

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Re: An extinction event (also known as a mass extinction or biotic crisis)   [#permalink] 09 Mar 2019, 07:25
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