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About 3 billion years ago, the Sun was only 80 percent as luminous as

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About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 10 Apr 2018, 09:28
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  95% (hard)

Question Stats:

53% (02:15) correct 47% (02:14) wrong based on 158 sessions

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About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth’s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth’s atmosphere through the presence of carbon dioxide, which, like methane, is a “greenhouse gas.” Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.

Which one of the following, if true, weakens the argument?

(A) Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity.

(B) Geological studies indicate that there is much less methane in Earth’s atmosphere today than there was 3 billion years ago.

(C) Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.

(D) The increase in the Sun’s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.

(E) Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun’s luminosity has resulted in more radiation reaching Earth.

Source: LSAT
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 10 Apr 2018, 09:40
IMO C.

About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth’s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth’s atmosphere through the presence of carbon dioxide, which, like methane, is a “greenhouse gas.” Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.Which one of the following, if true, weakens the argument?

(A) Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity.

- Out of scope

(B) Geological studies indicate that there is much less methane in Earth’s atmosphere today than there was 3 billion years ago.

- ok but that doesn't mean that levels of carbon dioxide was not high.

(C) Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.

Here you get an alternate reason as to why the oceans did not freeze. It tells that it is not CO2 infact minerals dissolved in water. Hold

(D) The increase in the Sun’s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.
- irrelevant

(E) Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun’s luminosity has resulted in more radiation reaching Earth.
- irrelevant...it is talking about the present.

Please confirm the OA.

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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 10 Apr 2018, 10:34
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ganand wrote:
About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth’s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth’s atmosphere through the presence of carbon dioxide, which, like methane, is a “greenhouse gas.” Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.

Which one of the following, if true, weakens the argument?

(A) Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity.

(B) Geological studies indicate that there is much less methane in Earth’s atmosphere today than there was 3 billion years ago.

(C) Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.

(D) The increase in the Sun’s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.

(E) Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun’s luminosity has resulted in more radiation reaching Earth.

Source: LSAT


The stimulus asserts that the earth's atmosphere should have more amount of green house gases than today to retain sun's heat to keep oceans from freezing. The statement concludes stating that carbon-di-oxide would have been much higher 3 billion years ago. But the argument seems to forget the fact that methane is also a green house gas. If the amount of methane gas is higher 3 billion years ago than today then It is possible that carbondioxide needn't necessarily be higher so option B states exactly that.
Option A is close however its possible that volcanic activity needs carbondioxide 3 billion years ago which doesn't weaken the argument completely.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 11 Apr 2018, 03:40
About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth???s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth???s atmosphere through the presence of carbon dioxide, which, like methane, is a ???greenhouse gas.??? Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.

Which one of the following, if true, weakens the argument?

(A) Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity.

(B) Geological studies indicate that there is much less methane in Earth???s atmosphere today than there was 3 billion years ago.

(C) Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.

(D) The increase in the Sun???s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.

(E) Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun???s luminosity has resulted in more radiation reaching Earth.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 11 Apr 2018, 04:55
About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth’s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth’s atmosphere through the presence of carbon dioxide, which, like methane, is a “greenhouse gas.” Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.

Which one of the following, if true, weakens the argument?

(A) Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity. this is direct heat. passage is about indirect heat. out of scope (OFS)

(B) Geological studies indicate that there is much less methane in Earth’s atmosphere today than there was 3 billion years ago.Yes ..there could high amount of methane more than CO2 acting as greenhouse gas billion years ago and keeping temperature high enough to melt ice.

(C) Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.no discussion about minerals. OFS

(D) The increase in the Sun’s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.it is talking about the life complexity not about the liquid phase conversion

(E) Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun’s luminosity has resulted in more radiation reaching Earth. so this will have same effect as it was billion years ago. no value addition.

Hence answer is B.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 11 Apr 2018, 14:48
Indresh wrote:
About 3 billion years ago, the Sun was only 80 percent as luminous as it is currently. Such conditions today would result in the freezing of Earth’s oceans, but geological evidence shows that water rather than ice filled the oceans at that time. Heat is trapped within Earth’s atmosphere through the presence of carbon dioxide, which, like methane, is a “greenhouse gas.” Only if the level of greenhouse gases were higher 3 billion years ago than it is today would Earth have retained enough heat to keep the oceans from freezing. It is likely, therefore, that the level of carbon dioxide in the atmosphere was significantly higher then than it is today.

Which one of the following, if true, weakens the argument?

(A) Sufficient heat to keep the oceans liquid 3 billion years ago could not have been generated through geological processes such as volcanic activity. this is direct heat. passage is about indirect heat. out of scope (OFS)

(B) Geological studies indicate that there is much less methane in Earth’s atmosphere today than there was 3 billion years ago.Yes ..there could high amount of methane more than CO2 acting as greenhouse gas billion years ago and keeping temperature high enough to melt ice.

(C) Geological evidence indicates that the oceans contained greater amounts of dissolved minerals 3 billion years ago, but not enough to alter their freezing points significantly.no discussion about minerals. OFS

(D) The increase in the Sun’s luminosity over the past 3 billion years roughly coincided with an increasing complexity of life forms on Earth.it is talking about the life complexity not about the liquid phase conversion

(E) Because the distance from Earth to the Sun has not changed significantly over the last 3 billion years, the increase in the Sun’s luminosity has resulted in more radiation reaching Earth. so this will have same effect as it was billion years ago. no value addition.

Hence answer is B.

Thanks Indresh for the explanation!

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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as  [#permalink]

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New post 19 Apr 2018, 05:15
We need to weaken the argument.means we need to find alternate reason for effect.an alternate explanation

Choice B clearly shows that due to methane ,temperature was rise enough in earlier time to keep water in liquid state.

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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as &nbs [#permalink] 19 Apr 2018, 05:15
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