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Most biologists agree that evolution takes place extremely slowly, wit

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Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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Most biologists agree that evolution takes place extremely slowly, with species requiring millions and millions of years to accumulate enough small changes to gradually transform into new ones. For the first 4 billion years of Earth’s history, the only species known were bacteria, plankton, and algae. But the fossil record indicates that during a brief 30 million year span known as the Cambrian explosion, the eventual lineages of all major animal groups alive today appeared.

Which of the following, if true, provides at least a partial explanation for the discrepancy outlined above?

A. The fossil record only represents a small portion of the species alive at any given time.
B. The fossil record indicates a number of major extinction events in Earth’s history.
C. Some of the lineages found in the fossil record of the Cambrian explosion are no longer alive today.
D. Bacteria, plankton, and algae leave little evidence in the fossil record because of their physical structures.
E. The fossil record indicates a large diversity in the plant species inhabiting the Earth during the Cambrian explosion.

Source: McGraw-Hill's GMAT
[Reveal] Spoiler: OA

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Re: Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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New post 05 Apr 2017, 05:46
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Good Question.

Statement 1: Evolution happens very slowly. Over several million years, a small change is transformed into a new ones.

Statement 2: Cambrian saw very big changes in just 30 million year span.

We need to find something that could help us clarify this discrepancy.

Best way to solve this question is to do POE.

B. The fossil record indicates a number of major extinction events in Earth’s history. : It no where tells us why they changed so much.
C. Some of the lineages found in the fossil record of the Cambrian explosion are no longer alive today. Fine, but what happened at that time?
D. Bacteria, plankton, and algae leave little evidence in the fossil record because of their physical structures. We are not concerned about these.
E. The fossil record indicates a large diversity in the plant species inhabiting the Earth during the Cambrian explosion. We already know this. This doesn't tell us why that happened.

A. The fossil record only represents a small portion of the species alive at any given time. : Ok, it means fossil records are not providing sufficient information. Although I donot agree with this option too much, I am 100% sure that other 4 are incorrect. Therefore, this is the best answer choice to mark.
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Re: Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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New post 08 Apr 2017, 14:37
Hi Can anybody please explain why the ans is 'B'? I did not much get the question.

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Re: Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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New post 08 Apr 2017, 23:00
arunavamunshi1988 wrote:
Hi Can anybody please explain why the ans is 'B'? I did not much get the question.


Dear arunavamunshi1988,

The answer is not B but A.

Please read the explanation I have given above. You may come up with any specific questions if you have.
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Re: Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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New post 12 Jul 2017, 03:12
iMyself wrote:
Most biologists agree that evolution takes place extremely slowly, with species requiring millions and millions of years to accumulate enough small changes to gradually transform
into new ones. For the first 4 billion years of Earth’s history, the only species known were bacteria, plankton, and algae. But the fossil record indicates that during a brief 30 million year span known as the Cambrian explosion, the eventual lineages of all major animal groups alive today appeared.

Which of the following, if true, provides at least a partial explanation for the discrepancy outlined above?

A. The fossil record only represents a small portion of the species alive at any given time.
B. The fossil record indicates a number of major extinction events in Earth’s history.
C. Some of the lineages found in the fossil record of the Cambrian explosion are no longer alive today.
D. Bacteria, plankton, and algae leave little evidence in the fossil record because of their physical structures.
E. The fossil record indicates a large diversity in the plant species inhabiting the Earth during the Cambrian explosion.

Source: McGraw-Hill's GMAT


If the fossil record only represents a small portion of the species alive at any given time, why it indicates ALL major animal groups during Cambrian explosion, whereas for the first 4 billion years of Earth’s history, it indicates ONLY THREE species?
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Re: Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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New post 25 Aug 2017, 01:05
Hi Mahmud6,
the passage mentioned:
But the fossil record indicates that during a brief 30 million year span known as the Cambrian explosion, the eventual lineages of all major animal groups alive today appeared.

this means that the fossil shows evidence of animal group known today but that does not mean all animal groups that had ever been existed are all existed today. there might be many extincted animal groups that we dont know about and their fossil is not available --> why A is correct.

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Re: Most biologists agree that evolution takes place extremely slowly, wit [#permalink]

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New post 25 Aug 2017, 03:01
How the option A provides explanation for the discrepancy outlined above? I am struggling to understand this?
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Re: Most biologists agree that evolution takes place extremely slowly, wit   [#permalink] 25 Aug 2017, 03:01
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