Earth's Magnetic Field

Answer choices

1. A

   Unsupported: not all9% picked this

   Most, but not all, geophysicists agree that the Earth’s magnetic field may exist in two

   It's hard to support this specific quantifier of "most, but not all". It means that it's "more than 50% but less than 100%". All we have to go off of is that it is a fundamental tenet of geophysics that magnetic field can exist in one of two states. If it's a fundamental tenet of the field of geophysics, it seems plausible that all modern geophysicists accept this idea, so we don't seem to have any support for the "but not all" part of this answer. In the real world, it's hard to imagine a 100% consensus on any scientific issue, but we have no visible textual support to justify saying "some geophysicists don't believe that polarity comes in two flavors".

   9%
2. B

   Correct65% picked this

   Changes in the polarity of the Earth’s magnetic field have occurred more often in the recent past than

   Why this is right

   This is a frustratingly worded answer, because who knows what we mean by "recent past vs. distant past"? Is there some quantitative precision to that idea? I guess lacking any other way to quantify recent past from distant past, we can just think "the more recent 2.25 billion years of Earth's history" vs. "the initial 2.25 billion years of Earth's history". In other words, divide Earth's history in half, and call the first half the distant past and the second half the recent past. Given that we were told in the middle of the 1st paragraph that these reversals have been taking place at an increasing rate, we could definitely say that there have been more reversals in the last 2 billion years than there were in the first 2 billion years. If I was making baskets at an increasing rate throughout a basketball game, then I would have made more baskets in the 2nd half than in the 1st half.

   Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.

   65%
3. C

   Unknown Comparison6% picked this

   Heat transfer would cause reversals of the polarity of the Earth’s magnetic field to occur more quickly

   Here, we're getting into the great unknowns of the speculative ideas within these two theories we hear about. The author never establishes a comparison that "hot and cold blobs perturbing the heat-circulation pattern" would happen more frequently than would "asteroid impacts causing redistribution of seawater". She only says that she finds an Earth-based explanation more convincing than an extraterrestrial explanation, but doesn't say it has anything to do with how frequently the causal mechanism of each theory would give rise to polarity reversals.

   6%
4. D

   Too Strong: increased significantly4% picked this

   Geophysicists’ understanding of the reversal of the Earth’s magnetic field has increased significantly since the introduction

   Since both of these theories are highly speculative and far from settled, we have no grounds for saying that geophysicists understanding has greatly improved since someone introduced the potential storyline of "maybe blobs cause the polarity shifts?"

   4%
5. E

   Wrong Friction Zone16% picked this

   Friction near the boundary of the inner and outer cores brings on reversal of the polarity

   The end of the 2nd paragraph implies that "friction and turbulence near the boundary of the outer core and the mantle" could initiate a polarity shift. This answer is claiming that friction between the boundary of the inner core and outer core could do it.

   16%