Self-study
P1
A vigorous debate in astronomy centers on an epoch in planetary history that was first identified by analysis of rock samples obtained in lunar missions. ██████████ ██████████ ████ ███ █████ ███████ ██ ███ ████ ████ ███████ ██ █ ████████ ███████████ ██ ██████ █████████████ ████ ███████ █████ █████████ █████████ ████ █████ ███████████ ██████ ███████████ ████ ████ ███████████ ████ ████████ ███ ████
Phenomenon ·
Late heavy bombardment
4 billion years ago, Moon and Earth were both massively bombarded with projectiles.
P2
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Hypothesis 1 ·
Large asteroid or comet disintegration
Evidence: size of lunar craters is large, suggests a large asteroid or comet broke apart and bombarded inner solar system with debris.
Hypothesis 2 ·
"LHB" is just a part of an even longer period of bombardment
"LHB" is part of a continuous bombardment that lasted billions of years. "LHB" just happened to be last and hence obliterated evidence of earlier impacts.
Hypothesis 3 ·
LHB only affected Earth-Moon system
Contra hypothesis 1 which claims that LHB affected entire inner solar system (Mars, Earth, Venus, and Mercury).
P3
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Evidence Supporting Hypothesis 1 ·
Mars rock found on Earth
Mars rock dates to same time as LHB, suggesting that Mars experienced bombardment too
Conclusion ·
LHB wasn't just an Earth-Moon phenomenon
At least Mars experienced it too.
Further Research ·
To decide between the different hypotheses
Passage Style
Critique or debate
Phenomenon-hypothesis (RC)
8.
Which one of the following ████ ██████████ █████████ ███ ████ █████ ██ ███ ████████
a
The LHB is ██ ███████ █████████ ███████████ ████ ████████ █████ ████ ███████ █████ ███ ███ ██ ███████████ ███ ███ █████████ ██ ███ ████ ███ ███████ ██ █████ ███████ ██ ███ █████ █████ ██████ ██ █████
(A) describes the LHB. However, the main point isn’t just the description of the LHB. Instead, the main point is that new
b
Astronomers now believe ████ ████ ███ █████ ███████ ██████ ████████ ██ █████████ ███ ████ ██████ ██ ███ ████
The passage doesn’t indicate that astronomers think that will never be enough evidence, so this can’t be the main point. The author
c
If scientists continue ██ ███████ ███ █████ ██ █████ ███████ █████ ███ ███████ ███ ██████████ ███ ████ ██ █████████ ███ █ █████ ███████ ████ ███████
The passage doesn’t discuss the rate at which evidence is currently being collected, nor does it suggest that the hypotheses will be evaluated “soon.” (C) isn’t supported by the passage, so it can’t be the main point.
d
The Moon's evidence █████ ████ ███ ███ ███ ██████ ██ █ █████ ████ ████ █████████████ █████ ██ █████ █████ ███ ███████ ███ █████ █████ ██████ ████ ███████
We know that the LBH has been attributed to
Also, (D) gives an explanation for the LHB. However, the main point of the passage is that new evidence has eliminated one potential hypothesis, but more evidence is needed in order to evaluate the remaining hypotheses. In other words, we don’t yet know what caused the LHB.
e
New evidence has ████ █████ ████ ██████ ███ ████ ████ ███ ███ ███ ███████████ ███ ██████ █████████ ████████ ██ ███ ███ ███ ██ █████████ ████ ████████ █████ ██ ██ █████████
This is the main point. The new evidence of the Mars rock has