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When the solar system condensed into being 4.6 billion years ago, the
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28 May 2026, 08:59
28 May 2026, 08:59
Expert Reply
Question 1
00:00
Question Stats:
65% (02:58) correct
35% (03:02) wrong based on 17 sessions
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Question 2
00:00
Question Stats:
56% (01:34) correct
44% (01:42) wrong based on 18 sessions
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When the solar system condensed into being 4.6 billion years ago, the nascent Sun radiated at merely three-quarters of its present luminosity. Nevertheless, the sedimentary strata of early Mars —preserved in the planet's ancient cratered highlands—betray no unambiguous signature of planet-wide cryogenic conditions until roughly 3.5 billion years ago. Kasting and Toon proposed in the 1980s that a dense carbon dioxide atmosphere, sustained by pervasive volcanism, trapped sufficient heat to maintain liquid water at the surface. However, subsequent geochemical modeling demonstrated that \(\mathrm{CO}_2\), even at the high partial pressures required, would condense into reflective clouds under the weak early Sun, drastically diminishing its greenhouse efficacy. A growing contingent of planetary scientists now posits that tidal flexure-gravitational kneading of Mars's interior by a then-much-closer moon or passing planetesimals-generated internal frictional heat that kept the subsurface and possibly the surface clement. This tidal-heating hypothesis offers a parsimonious explanation for the abrupt onset of Martian glaciation: around 3.5 billion years ago, orbital perturbations caused the perturbing body to migrate outward, where upon tidal stresses decayed exponentially and the geothermal supplement that had propped up the climate collapsed.
Which of the following best describes the function of the highlighted sentence?
A. It refutes the possibility of a causal connection between two phenomena that earlier theories had treated as interdependent.
B. It indicates how a particular hypothesis can account for the timing of an event mentioned earlier in the passage.
C. It presents evidence that undermines a claim advanced in the opening sentence of the passage.
D. It elucidates a distinction between two competing hypotheses that had previously been conflated.
E. It introduces data that challenge the prevailing explanation for a specific phenomenon.
Which of the following can be inferred from the passage about the tidal heating mechanism on early Mars?
A. The tidal heating mechanism must have ceased to operate entirely after 3.5 billion years ago.
B. The tidal heating mechanism must have produced effects that varied considerably across different latitudes of the Martian surface.
C. The warming generated by tidal flexure would have been more susceptible to diminution by cloud-albedo feedbacks than would warming from a dense \(\mathrm{CO}_2\) atmosphere.
D. The tidal heating mechanism could not have sustained clement surface conditions on early Mars without a contemporaneous \(\mathrm{CO}_2\) greenhouse effect.
E. The tidal heating mechanism would have been less consequential for early Martian climate if the perturbing body had migrated outward significantly earlier than 3.5 billion years ago.
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Re: When the solar system condensed into being 4.6 billion years ago, the
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30 May 2026, 03:45
30 May 2026, 03:45
Expert Reply
EXPLANATION #1
Explanation:
- A (Incorrect): No earlier theory treated two phenomena as "interdependent." The passage presents a sequence of rejected and currently favored hypotheses, not an interdependence claim that gets refuted.
- B (Correct): The passage earlier states that "sedimentary strata...betray no unambiguous signature of planet-wide cryogenic conditions until roughly 3.5 billion years ago" - this is the phenomenon (first glaciation) and its timing. The highlighted sentence then explains how the tidal-heating hypothesis accounts for why glaciation began at that specific time: the perturbing body migrated, tidal heating collapsed. The function is to show how the hypothesis explains the timing of the earlier-described event.
- C (Incorrect): The opening sentence states the faint young Sun fact (radiating at three-quarters luminosity). The highlighted sentence does not challenge this; it explains the timing of glaciation, which is downstream of the initial puzzle.
- D (Incorrect): The highlighted sentence does not distinguish between two hypotheses. It explains the mechanism by which the currently favored hypothesis accounts for a specific event. The distinction between $\mathrm{CO}_2$ and tidal heating occurs earlier in the passage.
- E (Incorrect): The highlighted sentence does not introduce "findings" or "data" that challenge the dominant explanation; the dominant explanation is the tidal-heating hypothesis. The sentence articulates how that hypothesis works, not evidence against it.
Explanation:
- A (Incorrect): No earlier theory treated two phenomena as "interdependent." The passage presents a sequence of rejected and currently favored hypotheses, not an interdependence claim that gets refuted.
- B (Correct): The passage earlier states that "sedimentary strata...betray no unambiguous signature of planet-wide cryogenic conditions until roughly 3.5 billion years ago" - this is the phenomenon (first glaciation) and its timing. The highlighted sentence then explains how the tidal-heating hypothesis accounts for why glaciation began at that specific time: the perturbing body migrated, tidal heating collapsed. The function is to show how the hypothesis explains the timing of the earlier-described event.
- C (Incorrect): The opening sentence states the faint young Sun fact (radiating at three-quarters luminosity). The highlighted sentence does not challenge this; it explains the timing of glaciation, which is downstream of the initial puzzle.
- D (Incorrect): The highlighted sentence does not distinguish between two hypotheses. It explains the mechanism by which the currently favored hypothesis accounts for a specific event. The distinction between $\mathrm{CO}_2$ and tidal heating occurs earlier in the passage.
- E (Incorrect): The highlighted sentence does not introduce "findings" or "data" that challenge the dominant explanation; the dominant explanation is the tidal-heating hypothesis. The sentence articulates how that hypothesis works, not evidence against it.
Re: When the solar system condensed into being 4.6 billion years ago, the
[#permalink]
30 May 2026, 04:00
30 May 2026, 04:00
Expert Reply
EXPLANATION #2
- A (Incorrect - too absolute): The passage states tidal stresses "decayed exponentially" and the geothermal supplement "collapsed," but "ceased to operate entirely" is stronger than warranted. Exponential decay approaches zero asymptotically; the passage doesn't assert complete cessation.
- B (Incorrect): The passage makes no mention of latitudinal variation. This is an out-of-scope distractor introducing a dimension (geographic variability) never discussed.
- C (Incorrect): The passage notes that \(\mathrm{CO}_2\) 's efficacy was diminished by reflective cloud formation. It never compares the relative susceptibility of tidal heating to cloud-albedo feedbacks. Tidal heating is geothermal, not atmospheric, so this comparison is unsupported.
- D (Incorrect): The passage presents tidal heating as an alternative to the $\mathrm{CO}_2$ hypothesis, not something that required \(\mathrm{CO}_2\) to function. The \(\mathrm{CO}_2\) hypothesis was challenged; tidal heating arose to fill the explanatory gap. No dependence is suggested.
- E (Correct): The passage establishes that glaciation began $\sim 3.5$ billion years ago because the perturbing body migrated outward around that time, causing tidal stresses to decay. If migration had occurred "significantly earlier," the geothermal supplement would have collapsed earlier, meaning the climate-propping effect would have been shorter-lived and thus "less consequential" for the early climate overall. This is a valid counterfactual inference directly supported by the causal logic of the passage.
- A (Incorrect - too absolute): The passage states tidal stresses "decayed exponentially" and the geothermal supplement "collapsed," but "ceased to operate entirely" is stronger than warranted. Exponential decay approaches zero asymptotically; the passage doesn't assert complete cessation.
- B (Incorrect): The passage makes no mention of latitudinal variation. This is an out-of-scope distractor introducing a dimension (geographic variability) never discussed.
- C (Incorrect): The passage notes that \(\mathrm{CO}_2\) 's efficacy was diminished by reflective cloud formation. It never compares the relative susceptibility of tidal heating to cloud-albedo feedbacks. Tidal heating is geothermal, not atmospheric, so this comparison is unsupported.
- D (Incorrect): The passage presents tidal heating as an alternative to the $\mathrm{CO}_2$ hypothesis, not something that required \(\mathrm{CO}_2\) to function. The \(\mathrm{CO}_2\) hypothesis was challenged; tidal heating arose to fill the explanatory gap. No dependence is suggested.
- E (Correct): The passage establishes that glaciation began $\sim 3.5$ billion years ago because the perturbing body migrated outward around that time, causing tidal stresses to decay. If migration had occurred "significantly earlier," the geothermal supplement would have collapsed earlier, meaning the climate-propping effect would have been shorter-lived and thus "less consequential" for the early climate overall. This is a valid counterfactual inference directly supported by the causal logic of the passage.
