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# About two million years ago, lava dammed up a river in western Asia

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About two million years ago, lava dammed up a river in western Asia  [#permalink]

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18 Dec 2015, 02:29
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65% (hard)

Question Stats:

60% (01:59) correct 40% (02:01) wrong based on 563 sessions

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About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava. Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Which one of the following is an assumption required by the argument?

(A) There were not other lakes in the immediate area before the lava dammed up the river.

(B) The lake contained fish that the human ancestors could have used for food.

(C) The lava under the lake-bottom sediments did not contain any human fossil remains.

(D) The lake was deep enough that a person could drown in it.

(E) The bones were already in the sediments by the time the lake disappeared.

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About two million years ago, lava dammed up a river in western Asia  [#permalink]

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02 Jan 2016, 14:12
nice question, choose E => we need to know that bones was already in sediment to make inference about 2 and 1.5 mln
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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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14 Jan 2016, 09:30
About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava.

Conclusion: Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Which one of the following is an assumption required by the argument?

(A) There were not other lakes in the immediate area before the lava dammed up the river...............we are not concerned about other lakes. OFS

(B) The lake contained fish that the human ancestors could have used for food...............human existence needs to be proved their food can be anything not only fish.

(C) The lava under the lake-bottom sediments did not contain any human fossil remains............sediments on top of lava does not mean that lava did not contain any fossil. This need not be assumed as this does not affect the conclusion.

(D) The lake was deep enough that a person could drown in it..................person death by drowning need not be assumed, he can die anywhere by any means and his fossil may have just floated in air to the lake.

(E) The bones were already in the sediments by the time the lake disappeared.............this is must to be assumed.
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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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07 Jun 2016, 07:29
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I am still confused why option C is wrong. Can somebody explain option C in more detail that why it's wrong?
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About two million years ago, lava dammed up a river in western Asia  [#permalink]

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07 Jun 2016, 09:34
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vnigam21 wrote:
I am still confused why option C is wrong. Can somebody explain option C in more detail that why it's wrong?

vnigam21

About two million years ago, lake formed

The lake existed for about 0.5 million years and Bones were recently found in the lake-bottom sediments on top of the layer of lava.

Conclusion: Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Do you get the gap of assumption in between the statements?

By the time of discovery, the bones were already there.

Since we got the bones at lake bottom it is understood that lake has dried up and if the conclusion that humans lived between that time period then the bones were already in the sediments by the time the lake disappeared/dried up.

so E is clearly visible as a right choice.

coming to C,
(C) The lava under the lake-bottom sediments did not contain any human fossil remains............

The fact that lava does not contain fossil remains while its seidments contain the fossil does not help anyway.

Even if we negate the statement i.e.,

The lava under the lake-bottom sediments do contain any human fossil remains. This supports the conclusion if not anything. This negation test proves that this cannot be the assumption...

I hope this helps
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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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07 Jun 2016, 10:27
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Gnpth wrote:
About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava. Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

 2m yrs ago ---> lava dammed up a river = Formation of a small lakeLake existed till 1.5 m yrs agoHuman bones found in the sediments on top of the layer of lava. Ancestors of Modern Humans lived = 2 m to 1.5 m years ago.

Try to negate option (E)

The bones were not there in the sediments by the time the lake disappeared = Bones were brought from somewhere and added to the lake sediments.

This clearly makes the argument fall apart....

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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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07 Jun 2016, 10:57
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Premise:- About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava.
Conclusion: - Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Which one of the following is an assumption required by the argument?

(A) There were not other lakes in the immediate area before the lava dammed up the river. - irrelevant

(B) The lake contained fish that the human ancestors could have used for food. - Irrelevant

(C) The lava under the lake-bottom sediments did not contain any human fossil remains - This is a trap answer if you read too fast as the premise states human remains were found on top sediments in lake bottom. Irrespective of the location with respect to lava layer this is not an assumption rather a mere statement of fact hence incorrect choice.

(D) The lake was deep enough that a person could drown in it - This is not an assumption rather a property of the lake and does not support the conclusion that humans existed because their remains were found in the lake.

(E) The bones were already in the sediments by the time the lake disappeared - Correct! This is the assumption that the author bases his/her conclusion on. The author assumes that human remains were already in the sediment on or before the lake disappeared on which basis the conclusion that humans existed when the lake existed is arrived at.
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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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11 Apr 2017, 00:06
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Gnpth wrote:
About two million years ago, lava dammed up a river in western Asia and caused a small lake to form. The lake existed for about half a million years. Bones of an early human ancestor were recently found in the ancient lake-bottom sediments on top of the layer of lava. Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

Which one of the following is an assumption required by the argument?

(A) There were not other lakes in the immediate area before the lava dammed up the river.

(B) The lake contained fish that the human ancestors could have used for food.

(C) The lava under the lake-bottom sediments did not contain any human fossil remains.

(D) The lake was deep enough that a person could drown in it.

(E) The bones were already in the sediments by the time the lake disappeared.

General Description: This question asks you to find the assumption required by the argument. In other words, find the statement whose truth is required if the argument is to succeed in demonstrating its conclusion.

A. Incorrect. The existence of other lakes in the area is irrelevant to the argument.

B. Incorrect. If response (B) turned out to be true, that might provide a reason why humans were in the area of the lake, but this particular explanation need not be assumed in order for the argument to succeed in demonstrating its conclusion.
C. Incorrect. It does not matter for the argument whether or not there were such remains in the lava, and the argument does not state or imply that there were no humans in the region prior to two million years ago. This was by far the most popular incorrect response.

D. Incorrect. The remains could have gotten into the lake in any number of other ways; to give just one, perhaps the people in the area put their dead into the lake.

E. Correct. If the bones were not already in the sediments when the lake dried up, that means that they got into the sediments later; that is, less than one-and-a-half million years ago. But then their existence would not provide evidence that there were human ancestors in western Asia between two million and one-and-a-half million years ago; that is, the conclusion of the argument would not follow if (E) is false.

Difficulty Level: Medium difficulty

Tips and Pitfalls: Another way to think about the question of whether an assumption is required by an argument is to think about what happens to the argument if the assumption turns out to be false. If the argument cannot possibly succeed when the assumption is false, then the assumption is required by the argument. Also, when asked for a necessary assumption, be careful not to pick an assumption that is stronger or broader than what is strictly necessary for the argument to succeed, even if making that assumption might strengthen the argument.
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About two million years ago, lava dammed up a river in western Asia  [#permalink]

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01 Nov 2017, 10:27
Here is a video explanation of this question by Ravi Sreerama,

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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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08 Feb 2019, 10:30
I understand option E.

If i negate option C the lava under the lake-bottom sediments did contain human fossils.

Doesnt this break the conclusion?
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Re: About two million years ago, lava dammed up a river in western Asia  [#permalink]

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08 Feb 2019, 10:41
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mallya12 wrote:
I understand option E.

If i negate option C the lava under the lake-bottom sediments did contain human fossils.

Doesnt this break the conclusion?

This is one of my all-time favorite distinctions to teach, because it has such a huge overarching lesson for how Critical Reasoning works. Look at what the exact conclusion is:

Therefore, ancestors of modern humans lived in Western Asia between 2 million and 1.5 million years ago.

And then look at what your negated C suggests, which is that ancestors of humans likely lived in Western Asia prior to 2 million years ago. Doesn't having humans live in that area even before the period we're talking almost kind of strengthen the argument? If I were to say "people lived in London in the 1980s" saying "well yeah but people lived in London in the 1960s" wouldn't negate that conclusion...if anything it makes it more likely because we've already established "people have lived in London."

Where people are so susceptible to picking C here is that they add their own words to the conclusion. If the conclusion were "the earliest ancestors of modern humans lived here between 2m and 1.5m years ago" then finding evidence that someone was there beforehand would attack the conclusion. But the conclusion doesn't have "the earliest" or "the first" in it at all! It just requires that human ancestors were there in that time period...if they were there before or after that period it doesn't matter.

So the lesson is that the specificity of the conclusion is everything...you have to know exactly what the conclusion says (and what it doesn't say), because trap answers are set to entice people who are just a little bit off of that specific scope of the conclusion.
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Re: About two million years ago, lava dammed up a river in western Asia   [#permalink] 08 Feb 2019, 10:41
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