Impact Craters

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vikram_k51: Master | Next Rank: 500 Posts; Posts: 208; Joined: Sat Jan 31, 2009 11:32 am; Location: Mumbai; Thanked: 2 times

by vikram_k51 » Wed Aug 19, 2009 9:05 am

Impact craters caused by meteorites smashing into Earth have been found all around the globe, but they have been found in the greatest density in geologically stable regions. This relatively greater abundance of securely identified crater in geologically stable regions must be explained by the lower rates of destructive geophysical processes in those regions.
The conclusion is properly drawn if which one of the following is assumed?
(A) A meteorite that strikes exactly the same spot as an earlier meteorite will obliterate all traces of the earlier impact.
(B) Rates of destructive geophysical processes within any given region vary markedly throughout geological time.
(C) The rate at which the Earth is struck by meteorites has greatly increased in geologically recent times.
(D) Actual meteorite impacts have been scattered fairly evenly over the Earth's surface in the course of Earth's geological history.
(E) The Earth's geologically stable regions have been studied more intensively by geologists than have its less stable regions.
OA D

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Source: Beat The GMAT — Critical Reasoning | Wed Aug 19, 2009 9:05 am

mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Wed Aug 19, 2009 7:31 pm

IMO - D

You need to assume this to make the argument more convincing - Actual meteorite impacts have been scattered fairly evenly over the Earth's surface in the course of Earth's geological history.

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delhiboy1979: Master | Next Rank: 500 Posts; Posts: 239; Joined: Wed Feb 11, 2009 2:50 am

by delhiboy1979 » Wed Aug 19, 2009 11:00 pm

Isnt D contradicting what is mentioned on the stem. If the meteorite strikes were scattered evenly, then how does one justify that only the geologically stable areas are most prone to the strike.

Vikas, what is the source of this.

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mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Thu Aug 20, 2009 1:22 am

Argument doesn't says that geologically prone areas are more prone to the strike...

Argument says "Impact craters caused by meteorites smashing into Earth have been found all around the globe, but they have been found in the greatest density in geologically stable regions."

Now why's that -

This relatively greater abundance of securely identified crater in geologically stable regions must be explained by the lower rates of destructive geophysical processes in those regions.

Now lets look at the answer choice D - In order to make the conclusion more convincing, you would have to assume that the strikes were evenly distributed over the geographical regions.

If you reverse this option, lets say the strikes were more in the stable regions and less in the regions that were less stable.

Then the conclusion cannot be properly drawn.

delhiboy1979 wrote:Isnt D contradicting what is mentioned on the stem. If the meteorite strikes were scattered evenly, then how does one justify that only the geologically stable areas are most prone to the strike.

Vikas, what is the source of this.

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gmatmachoman: Legendary Member; Posts: 2326; Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members; Thanked: 173 times; GMAT Score:710

by gmatmachoman » Thu Aug 20, 2009 6:01 am

man this CR is tuffffff..

I am down for this

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ranell: Master | Next Rank: 500 Posts; Posts: 224; Joined: Mon May 04, 2009 2:44 pm; Location: Russia, Moscow; Thanked: 10 times; GMAT Score:730

by ranell » Thu Aug 20, 2009 1:18 pm

Explanation is given below:

(A) It doesn't matter whether or not earlier meteorites will obliterate the traces of the previous meteorites that fell on the Earth
(B) If rates of destructive geological processes vary markedly within any given region through geological time, the number of craters caused by meteorites also varies within this given region, but it doesn't explain the abundance of craters in a particular region at a particular moment
(C) The fact that the rate of destructive processes has increased doesn't presuppose the abundance of craters in a particular region at a particular moment
(D) CORRECT as if the number of craters caused by meteorites was initially the same on the surface of the Earth, then the conclusion that the abundance of craters in a particular region is explained by the lower rates of destructive geophysical processes in those regions is plausible
(E) How the Earth's different regions were studied is out of scope in the argument

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akuma: Junior | Next Rank: 30 Posts; Posts: 29; Joined: Tue Dec 15, 2009 8:37 pm; Thanked: 3 times

by akuma » Tue Feb 07, 2012 11:42 am

Remember that the assumption is the missing "link" between the premise and conclusion.

I will make this awfully simple.

Premise: Impact craters are clumped together (not evenly distributed) around the world.
Conclusion: These impact crater clumps exist because there is hardly any weathering in these areas.

(D) Actual meteorite impacts have been scattered fairly evenly over the Earth's surface in the course of Earth's geological history.

The assumption will support the conclusion and must be true. If the assumption is negated and the conclusion is destroyed, then you have your answer.

In other words, an assumption, as in this case, serves to validate the conclusion.

Answer choice D, if negated, would say something like.. Meteors strike in certain places more often than other places in the world. This negation completely destroys the conclusion because it offers an alternative explanation to why craters are clumped together.

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