PrepTest 133, Section 4, Question 21

Working the answers

• A
  Correct

  At first, near the continents may look like a location we didn't discuss directly. But follow the movement: the rocks are youngest near the ridge and become older as their distance from the crest increases (paragraph 3). Rock that has been pushed far outward toward the continental edges is therefore likely to be among the oldest. This is an inference from that age-and-distance relationship, not a quotation we need to find word for word.

• B

  Earth reverses its magnetic field; solid basalt keeps the alignment recorded when it cooled. An older sample hasn't necessarily reversed its own polarity at all.

• C

  We aren't given a comparison of how often compasses are distorted at sea versus on land. Mentioning land distortion doesn't establish the ranking C claims.

• D

  Nothing says the magnetite's field gradually weakens. Age is linked to location and the recorded orientation, not to a stated loss of magnetic strength.

• E

  Present-day polarity can also match an older period before intervening reversals. An old rock formed during an earlier normal-polarity period could still have that alignment today. Matching the current field doesn't, by itself, date the rock to after the latest reversal.