PrepTest 133, Section 4, Question 18
Until the 1950s, most scientists believed that the(440 more words not shown)
According to the passage, which(9 more words not shown)
- AIn the youngest(9 more words not shown)
- BIn magma, most(12 more words not shown)
- CThey are not(8 more words not shown)
- DThey are about(7 more words not shown)
- EThey are too(8 more words not shown)
Reading the passage
Magnetite grains follow Earth's magnetic field while the rock is molten, then keep that alignment when the rock hardens. That's what I remember about them. We'll check the choices against that account and the later evidence.
Working the answers
- ACorrect
This seems to follow from recently formed rock recording the current field, and the third paragraph gives direct support: all the newest rocks share normal polarity (paragraph 3). The first paragraph defines normal polarity as matching Earth's present field. Put those two statements together and we have A.
- B
This introduces exceptions to alignment in molten rock that aren't described. Reversed polarity doesn't supply such an exception: those grains aligned with Earth's field when they formed, too. The field's direction was different then.
- C
Finding magnetite in basalt doesn't establish that no other kind of rock contains it. We aren't given that restriction.
- D
Nothing compares magnetite grains with grains of sand. Using the same word doesn't establish the same size.
- E
Their visibility to the naked eye isn't discussed. We know how they align, not whether we could see an individual grain.
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