PT 63, Geology of the Ocean Floor Passage, #19

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timmydoeslsat

Posts: 148
Joined: Wed Aug 03, 2011 2:07 pm

PT 63, Geology of the Ocean Floor Passage, #19

I have a great grasp on this passage, as this stuff interests me, but I cannot understand how (C) is likely to be true at all.

When I saw the question stem telling me that if time intervals between the earth's magnetic field reversals fluctuate greatly...I did not know how to tie that in with my understanding of the passage.

I know from the passage that the earth's magnetic fields reverses its polarity. I do not know if it is at a consistent rate, a fluctuating rate?

So by this question stem telling me about a hypothetical situation of the time interval of these reversals fluctuating greatly...I do not know what to make of it.

I will say this, the last part of the final paragraph states that if we assume that the floor moved away from the spreading center at a rate of several cm's per year...that may indicate a constant rate, but we are assuming that.

I do not know how that constant rate ties in magnetic stripes of basalt being much wider than others.

RonnyDworkin

Posts: 257
Joined: Tue Mar 09, 2010 12:01 am

Re: PT 63, Geology of the Ocean Floor Passage, #19

timmydoeslsat wrote:I have a great grasp on this passage, as this stuff interests me, but I cannot understand how (C) is likely to be true at all.

When I saw the question stem telling me that if time intervals between the earth's magnetic field reversals fluctuate greatly...I did not know how to tie that in with my understanding of the passage.

I know from the passage that the earth's magnetic fields reverses its polarity. I do not know if it is at a consistent rate, a fluctuating rate?

So by this question stem telling me about a hypothetical situation of the time interval of these reversals fluctuating greatly...I do not know what to make of it.

I will say this, the last part of the final paragraph states that if we assume that the floor moved away from the spreading center at a rate of several cm's per year...that may indicate a constant rate, but we are assuming that.

I do not know how that constant rate ties in magnetic stripes of basalt being much wider than others.

I'm a little confused about your post, but I'll give it a try.

I did well on this passage and RC (thinking back I really can't say how). I ended up missing 0 on RC. So this reply is based on my vague memory of the question.

Think of it as a quantitative problem. If the rate of flow is constant, but the time period between polarity changes fluctuates invariably, then you will end up with variations in the width of the bands (i.e., where a distinct band is defined by difference in polarity).

So let's say magma comes out at 1 inch a day, and in our hypo world starting on day 1 (D1) the polarity is north. Then let us assume that the next day (D2) the polarity switches to south. On D3 the polarity is still south, and the same for D4. On D5 the polarity switched to north. So relation wise it would look something like this

D(1, north) = 1 day = 1 inch
D(2-4, south) = 3 days = 3 inches
D(5 - ...., north) = ? days = ? inches

timmydoeslsat

Posts: 148
Joined: Wed Aug 03, 2011 2:07 pm

Re: PT 63, Geology of the Ocean Floor Passage, #19

Thanks so much for the post.

I understand how it can be wide, but how do you know that it will be wider than others?

Would it not be the case that all of them move in likewise fashion?

Or am I to assume that some of the basalt has been walled off in terms of its polarity and will stay put regardless of a change in polarity.

Is my thinking correct on this?

Tiago Splitter

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Joined: Tue Jun 28, 2011 1:20 am

Re: PT 63, Geology of the Ocean Floor Passage, #19

timmydoeslsat wrote:Thanks so much for the post.

I understand how it can be wide, but how do you know that it will be wider than others?

Would it not be the case that all of them move in likewise fashion?

Or am I to assume that some of the basalt has been walled off in terms of its polarity and will stay put regardless of a change in polarity.

Is my thinking correct on this?

It asks what would happen if the time intervals fluctuate greatly. The passage doesn't say whether this is or isn't the case. The question just presents a new hypothetical.

When the polarity changes, a new band forms. The old ones stay in place. The longer the same polarity exists, the wider the newly forming band will be.

timmydoeslsat

Posts: 148
Joined: Wed Aug 03, 2011 2:07 pm

Re: PT 63, Geology of the Ocean Floor Passage, #19

I totally understand it now. Thanks so much.