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passage 2
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
12.
According to the passage, the
a
affected only the ████
b
was so brief ████ ███ ██████ ███ ██ ██ ██████ █████████
c
consisted of so ██████ ██████ ████ ██ ███ ████████ ███████ ██ ███ ███████ ██ ███ █████ █████ ██████
d
occurred more recently ████ ████ ███████ █████ ███
e
may have lasted █ ████ █████ ███ ███ ███ ██████ ████████ ██████ ███ ██████████ ██████