RC PrepTest A Feb1996 3 Passage "Continental drift"

Walrus
Posts: 38
Joined: Sat Oct 19, 2013 12:04 am

RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby Walrus » Tue Jan 14, 2014 5:58 pm

This is a descriptive passage that tells us a story how continental drift theory became widely accepted. Passage consecutively presents discoveries, that contributed to its widespread acceptance. Third paragraph presented Keith Runcorn's evidence for drift. I can't grasp how in the world his evidence could support theory of continental drift.

Here is his evidence:
When volcanic lava turns into basalt it fixes earth's current magnetic field.
"Although one would expect that the magnetic fields of rocks of the same age from any continent would all be aligned the way the earth's magnetic field was aligned at that time, the magnetic fields of basalt in North America are now aligned quite differently from rocks formed in the same epoch in Europe. Thus...clear evidence that the continent drifted.

Here is illustration of what Runcorn is talking about
http://www.youtube.com/watch?v=hSdlQ8x7cuk

As far as I understand Earth doesn't have different magnetic fields. There are two possible options: N to S or S to N. And the fact that magnetic fields in basalt in NA aligned differently from rocks formed in the same epoch in Europe sounds like anomaly.

If someone has an idea what is going on please help!

Captainunaccountable
Posts: 93
Joined: Sat Jan 04, 2014 1:36 pm

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby Captainunaccountable » Tue Jan 14, 2014 6:45 pm

Walrus wrote:This is a descriptive passage that tells us a story how continental drift theory became widely accepted. Passage consecutively presents discoveries, that contributed to its widespread acceptance. Third paragraph presented Keith Runcorn's evidence for drift. I can't grasp how in the world his evidence could support theory of continental drift.

Here is his evidence:
When volcanic lava turns into basalt it fixes earth's current magnetic field.
"Although one would expect that the magnetic fields of rocks of the same age from any continent would all be aligned the way the earth's magnetic field was aligned at that time, the magnetic fields of basalt in North America are now aligned quite differently from rocks formed in the same epoch in Europe. Thus...clear evidence that the continent drifted.

Here is illustration of what Runcorn is talking about
http://www.youtube.com/watch?v=hSdlQ8x7cuk

As far as I understand Earth doesn't have different magnetic fields. There are two possible options: N to S or S to N. And the fact that magnetic fields in basalt in NA aligned differently from rocks formed in the same epoch in Europe sounds like anomaly.

If someone has an idea what is going on please help!


I don't know anything about this. I don't care about continental drift. I don't understand, though, why it exactly matters. Your job isn't to critique the passage's argument, rather understand the argument. It doesn't matter if it's true or not true based on whatever knowledge you may have or research you may have done outside of the passage.

Walrus
Posts: 38
Joined: Sat Oct 19, 2013 12:04 am

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby Walrus » Wed Jan 15, 2014 12:38 am

I don't understand, though, why it exactly matters

It matters because of Q20. It asks to undermine evidence for the theory of continental drift.
Your job isn't to critique the passage's argument, rather understand the argument

I don't understand the argument. It doesn't make sense to me. That is why I am asking for help.
It doesn't matter if it's true or not true based on whatever knowledge you may have or research you may have done outside of the passage.

I agree with you. But I am trying to use all means to understand how did this particular evidence support theory. It is not for criticizing the passage but rather in order to understand it.

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Christine (MLSAT)
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Joined: Fri Nov 22, 2013 3:41 pm

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby Christine (MLSAT) » Wed Jan 15, 2014 1:05 am

So, treat this like a logical reasoning argument core:

    PREMISES
    When lava turns to basalt, it aligns with the current magnetic field.
    Rocks formed in the same era would have the same magnetic alignment [i]when formed
    .
    Rocks from a certain era in Europe have a different alignment now then those in North America from the same era.[/i]

    CONCLUSION
    The rocks (or continents they were on), must have moved between formation and now (i.e., continental drift).

Based on what we're told about the alignment, those North American and European rocks had to have been aligned the same way when they first formed. But now they are not aligned the same way. If it's *not* just 'an anomaly', what could explain it? The alignment of the rock can't change, so it must be that the rock moved.

It's just like placing two pieces of paper on a table and then drawing a vertical line down the middle of each. They are parallel when you do this. Now take one of the pieces of paper and spin it a little. Now the lines aren't parallel. That spinning of the paper is continental drift.

Does that help?

Walrus
Posts: 38
Joined: Sat Oct 19, 2013 12:04 am

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby Walrus » Wed Jan 15, 2014 1:24 am

Makes perfect sense now. Thank you!!!

Augy1
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Joined: Fri Oct 25, 2013 12:05 pm

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby Augy1 » Wed Jan 15, 2014 3:02 am

What is the general consensus regarding RC passages from the Superprep tests? Do they reflect the current difficulty of RC passages or are they much easier?

i like redheads
Posts: 21
Joined: Wed Apr 08, 2015 10:35 am

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby i like redheads » Thu Apr 16, 2015 4:22 am

Yeah I'm still not understanding this section of the passage and Q20

i like redheads
Posts: 21
Joined: Wed Apr 08, 2015 10:35 am

Re: RC PrepTest A Feb1996 3 Passage "Continental drift"

Postby i like redheads » Thu Apr 16, 2015 4:27 pm

In particular, why is D not the credited response?




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