Passage Discussion

[legalrabbithole]

I'm pretty confused by the 2nd paragraph-- can someone please paraphrase what they're saying?

For #19, I picked (A) because there's nothing against peaks..however, I can see how it's considered unsupported. I just don't get how (C) is the right answer since width doesn't seem to be covered either.

[demetri.blaisdell]

As I see it, the general layout of the passage is:

1st P: Old theory (sea floor unchanged for millions of years) and background information (polarity of basalt corresponds to polar alignment).

2nd P: Background (mid-ocean ridge) and New theory of Ocean Floor Spreading (ocean floor being spread apart and magma filling in the space).

3rd P: Using background info from 1st and 2nd Ps to support the new theory.

I hope that helps to put the 2nd paragraph in context by removing some of the details. Let me know if you want more general explanation about this.

As for question 19, the key is to focus on the last paragraph. Lines 49-56 show that the ocean floor is spreading at a constant rate. If the planet's polarity were switching at a fixed rate, then the bands of rock would be laid out in even bands. But, if the polarity were to be switching at irregular time intervals, the bands would be different widths. You get this in (C).

(A) doesn't use the new information (about the intervals being irregular). Also, do we have any way of knowing that there is more basalt at the peaks? More importantly, basalt causes compasses to malfunction on land, but does that also happen underwater?

I hope this helps clear up your questions. Let me know if you want more about any of this.

[obobob]

HI just a quick Q about the first paragraph.
Can anyone help me summarizing functions of the contents in the first paragraph?

I was sort of thrown off when I read the first three sentences. So are the sentences from the third sentence (“First, scientists noticed that the ocean floor exhibited ...”) to the rest of the paragraph going against the old belief in the first sentence?

[smiller]

I was sort of thrown off when I read the first three sentences. So are the sentences from the third sentence (“First, scientists noticed that the ocean floor exhibited ...”) to the rest of the paragraph going against the old belief in the first sentence?

Yes, that's essentially what's going on.

The passage starts contradicting the old belief right away, right in the second sentence ("But this idea became unsupportable..."). The third sentence starts to describe the new discoveries that made the old idea unsupportable. "First" indicates that the discovery of the odd magnetic variations was the first of the new discoveries mentioned in the previous sentence.

The rest of the first paragraph provides more information about these magnetic variations. The rest of the first paragraph—and really, the rest of the passage—builds off of these first three sentences.