RC: Before the age of space exploration, astronomers assumed

[NL]

I practice Ron’s strategy for detail questions and have a question at the end.

Passage: Before the age of space exploration, astronomers assumed that the Moon's core was smaller than the Earth’s, in both relative and absolute terms - the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass - but they had no way to verify this. Two sets of data gathered by Lunar Prospector have now given astronomers the ability to determine that the Moon's core accounts for 20 percent of the Moon's radius and for a mere 2 percent of its overall mass.

First, scientists measured minute, relatively rapid variations in the wavelength of radio signals from Lunar Prospector as the craft moved towards or away from the Earth. Using these variations, scientists accurately determined even slight changes in the craft's velocity while the craft orbited the Moon, changes resulting from inconsistency in the gravitational pull of the Moon on the craft. The data were used to create a "gravity map" of both near and far sides of the Moon, highlighting new details of the distribution of the Moon's internal mass. Scientists thus determined that the Moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the Moon itself by the Moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.

The size and composition of the Moon's core have serious implications for our understanding of the Moon's origins. If the Moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the Moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps due to a major asteroid impact that could have loosened a chunk of iron, allowing it to form the core around which the Moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.


It can be inferred from the passage that the impact theory and the fission theory of the Moon’s origin are similar in that they both

A. explain the congruence in the size and mass of the Earth’s and the Moon’s cores
B. assert that the Moon did not predate the Earth
C. imply the development of the Earth and Moon as distinct entities
D. propose that iron ejected from the Earth coalesced the rest of the Moon through magnetic attraction
E. account for the inconsistency in the gravitational pull of the Moon

Answering the question:

- What? The similarity of the impact theory and the fission theory
- Where? The last paragraph
- Write down:
Theory 1: moon was a part of the earth.
Theory 2: moon was independent from the earth.
- Choices: no choice seems to relate to the paragraph’s point. So I thought about eliminating choices (like for EXCEPT questions)

Do you have any other way to reach the answer more quickly?

(MGMAT CAT. OA: B)

[RonPurewal]

- Choices: no choice seems to relate to the paragraph’s point.

This is a detail question. On detail questions, larger "points" are irrelevant.
You just need to pick the choice that MUST BE TRUE, and that re-packages the existing information.

It's like arguing over a contract. If something isn't IN the contract, and/or implied by foolproof logic from stuff in the contract, then ... it's not a thing.

[RonPurewal]

Your inventory of information here ("the contract", in the analogy above) is the information in the last few lines, which describe the two theories mentioned.

Just see which choice follows from the information in those lines.

A/
Contradicts the given information.
The last paragraph says that, if something (that isn't true) were true, then the earth's and moon's cores "should be more comparable". It then goes on to state that, "in actuality", the truth lies in opposition to that idea.

B/
One theory holds that an asteroid knocked a chunk of iron out of the Earth, and that the Moon then formed around that chunk (in the same way clouds form around random pieces of dust in the sky).
The other theory says that the Earth just chucked a bunch of stuff into outer space by the sheer force of rotating so fast, and that the Moon formed from that stuff.
Both theories claim that the Moon was, in one way or another, formed from the Earth. If that's true, then, clearly, the Earth had to have been there first, so this choice must be true.

C/
The whole point of both theories is to disprove this idea.

D/
This is just the first theory.

E/
Not in this paragraph at all.

[NL]

Both theories claim that the Moon was, in one way or another, formed from the Earth.

Hum, I misunderstood the second theory:

"Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon."

Does "coalesce into" = form? Little weird.

I understood the sentence above like this: The Earth and the Moon have existed as 2 independent entities, then the Moon attracted some materials from the Earth.
How should the sentence be written so that this meaning is conveyed? (I try to differentiate)

[RonPurewal]

Both theories claim that the Moon was, in one way or another, formed from the Earth.

Hum, I misunderstood the second theory:

"Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon."

Does "coalesce into" = form? Little weird.

http://www.merriam-webster.com/dictionary/coalesce

I understood the sentence above like this: The Earth and the Moon have existed as 2 independent entities, then the Moon attracted some materials from the Earth.

You can rule out this interpretation by remembering that the author is talking about the origins of the Moon.
If these words meant "The Earth spit out a bunch of material, which then slammed into the (already existing) Moon", then this whole bit would have nothing to do with the Moon's origins!

[RonPurewal]

How should the sentence be written so that this meaning is conveyed? (I try to differentiate)

There are a million zillion different ways in which you could write it.
e.g., "which was later drawn into the Moon by gravitational attraction"

[NL]

You can rule out this interpretation by remembering that the author is talking about the origins of the Moon.

Good point, Ron. "Branch" ideas should support main ideas.

There are a million zillion different ways in which you could write it.
e.g., "which was later drawn into the Moon by gravitational attraction"

I don’t care about million zillion ways, just care about a good way. Here it is. So the issue lies on "coalesce", not "into". The word "into" give me a sense that something must be exist before other things can get into.

(Thanks for the nice-colorful dictionary. I did check it before asking because I was still confused)

[RonPurewal]

The word "into" give me a sense that something must be exist before other things can get into.

You could only get that sense if you forgot that you were reading a passage about the origins of the Moon.

Don't forget the context!

Thanks for the nice-colorful dictionary.

You're welcome.
(:

[janec963]

hi, Ron. i have the following question.

The primary purpose of the passage is best expressed in which of the following ways?
a. The author presents the data set that proved that the Moon was once part of the Earth.
b. The author discusses the data sets that changed scientists' opinions about the relative sizes of the Earth's and the Moon's cores.
c. The passage analyzes the assumptions about radii and core mass that led to important implications about the origin of the planets.
d. The passage examines the use of scientific methods to analyze data and confirm a hypothesis, while referencing possible deductions.
e. The passage elucidates the implications following from the size of the Earth's core.

i choose c, but OA is d.
actually, when i answer this question, i think that ' examines the use of scientific methods' in d is wrong. in my view, the passage just uses the methods to justify the assumption about the Moon, not examines.

So, can you help me explain why d is right and why c is wrong?
thanks in advance.