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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 16 Feb 2016, 03:22
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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.

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.



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.
[/box_out]

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.
[/box_out]

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.
[/box_out]




OA : c , d ,d d

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

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New post 16 Feb 2016, 18:49
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i got d,d,d,d .

let me know if it is correct
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Re: An extinction event (also known as a mass extinction or biotic crisis) [#permalink]

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New post 16 Feb 2016, 22:24
my answers are
1) d
2) b
3) d
4) d
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Re: An extinction event (also known as a mass extinction or biotic crisis) [#permalink]

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New post 17 Feb 2016, 00:12
IMO
1> D
2> A
3> D
4> D

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

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New post 17 Feb 2016, 07:32
Could anyone please explain as to why for last question the answer cannot be C?
I thought he was explaining the extinction theory through out the passage.
and presented evidence in last paragraph as well.

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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 Feb 2016, 04:28
Mahamalik

the passage doesnt provide any new information or evidences...it talks about past 5 massive extinction and mention one of them. hope this helps
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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 Feb 2017, 07:18
Can anyone please explain the ans of question 2?

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

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New post 08 Apr 2017, 05:23
I have a query over OA of question 3.

There are two types of extinctions which are mentioned in the passage.
1. Background Extinctions
2. Mass Extinctons


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


This clearly says that mass extinctions caused sharp change in the diversity.

So how can we eliminate A over C?

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

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New post 20 Apr 2017, 20:14
can we please get OA? i did them and got d, d, d, d (as one user) but i'm not entirely sure. this was a brutal passage

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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 Apr 2017, 02:35
IMO

DACD

Waiting for the OA. Infact OA's should be present in RC question at the time of posting. It really helps gauging performance.

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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 Apr 2017, 05:07
There is no OA on this question, please have this sorted.
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Re: An extinction event (also known as a mass extinction or biotic crisis)   [#permalink] 21 Apr 2017, 05:07
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