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)
13.
Which one of the following, ██ █████ █████ ████ ███ ████ ███████ ██ ███ ████ ████ ███ ███ ███ ███████ ██ █████ ███ ███ █████
a
An extensive survey ██ ███████ ██ ████ █████ ████ ██████ ████████ ███ ██ ████████ ██ ███ █████████ ██ ███████████ ████████ ████ ██████ ███ ██████ ████ █████ ███████ ██ ████ ███████ █████ ████
(A) destroys Hypotheses 1 and 2. Both of these hypotheses hinge on a period of heavy bombardment through the inner solar system that intensified four billion years ago. If new evidence showed that Mars did not experience an increase in the intensity of projectiles between three billion to five billion years ago, then we know that there actually wasn’t a period of heavy bombardment through the inner solar system four billion years ago, thus eliminating Hypothesis 1 and 2 and leaving Hypothesis 3 as our only option.
Additionally, (A) tells us that there was not a period of heavy bombardment on Mars four billion years ago, meaning that the Mars rock discovered on Earth would have been a rare discovery of a coincidence, instead of evidence of a larger trend.
b
Scientists discover another █████████ ██ █████ ████ ████ ████████ ███ ████ ███████ ████ ███ ███████ ██ ███ ████ ██████ ███ ████
Even Hypotheses 1 and 2 allow for debris from the Moon to reach the Earth––these hypotheses just say that the LHB extended beyond the Earth-Moon system. We already
c
A re-analysis of ████ █████ ███████ ████ ███████ ██████████ ██ █████ ██████ ███ ████
It’s generally
d
Based on further ████████ ██████████ ████████ ████ ███ ████ ████████ ██ ████ ██████████ ██ ████ ████████ ██████████ ██ ███ █████
(D) weakens the author’s elimination of Hypothesis 3. However, this just puts Hypothesis 3 on a level playing field with Hypotheses 1 and 2. Additionally, (D) only addresses one
Compare this with (A), which strengthens Hypothesis 3 and destroys Hypotheses 1 and 2.
e
Excavations on both █████ ███ ███ ████ █████ ████████ ████ ███ ███ █████████ ████████ ██ █████ ██ █████ ████████████
It’s