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

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ganand
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About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink] New post   10 Apr 2018, 09:28
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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] 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] 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.

Sent from my Lenovo K53a48 using GMAT Club Forum mobile app
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink] 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] 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] New post   11 Apr 2018, 14:48
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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!

To post additional questions not already addressed in this thread, feel free to use the request verbal experts' reply button.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink] New post   19 Apr 2018, 05:15
We need to weaken the https://gmatclub.com/chat 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 [#permalink] New post   11 May 2020, 07:00
Premise is that gases were higher than in the past x in the present - explaining why oceans were water rather than frozen. We need to weaken this, and the answer is (B). But in my opinion, (B) is strengthening. Please help.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink] New post   17 May 2020, 15:15
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exc4libur wrote:
Premise is that gases were higher than in the past x in the present - explaining why oceans were water rather than frozen. We need to weaken this, and the answer is (B). But in my opinion, (B) is strengthening. Please help.


Hi

Let me try to address your query.

There is an important difference between what you have stated and the conclusion as mentioned in the stimulus.

The conclusion is not merely that "gases were higher in the past than in the present". The conclusion specifically states: "the level of carbon dioxide in the atmosphere was significantly higher then than it is today".

Therefore, we need an answer option that weakens the assertion that "carbon dioxide" in the earth's atmosphere was higher 3 billion years ago than it is today.

Now, the stimulus tells us the following:

1) ...carbon dioxide, which, like methane, is a “greenhouse gas.”
2) 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.

Therefore, it is enough for some greenhouse gases to have been higher 3 billion years ago than today - it need not specifically be carbon dioxide. Option (B) tells us that the levels of methane were higher 3 billion years ago than today. Therefore, this could have retained enough to heat keep water in liquid form without necessitating higher levels of carbon dioxide. Thus this weakens the conclusion.

Hope this helps.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink] New post   17 May 2020, 15:45
svasan05 wrote:
exc4libur wrote:
Premise is that gases were higher than in the past x in the present - explaining why oceans were water rather than frozen. We need to weaken this, and the answer is (B). But in my opinion, (B) is strengthening. Please help.


Hi

Let me try to address your query.

There is an important difference between what you have stated and the conclusion as mentioned in the stimulus.

The conclusion is not merely that "gases were higher in the past than in the present". The conclusion specifically states: "the level of carbon dioxide in the atmosphere was significantly higher then than it is today".

Therefore, we need an answer option that weakens the assertion that "carbon dioxide" in the earth's atmosphere was higher 3 billion years ago than it is today.

Now, the stimulus tells us the following:

1) ...carbon dioxide, which, like methane, is a “greenhouse gas.”
2) 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.

Therefore, it is enough for some greenhouse gases to have been higher 3 billion years ago than today - it need not specifically be carbon dioxide. Option (B) tells us that the levels of methane were higher 3 billion years ago than today. Therefore, this could have retained enough to heat keep water in liquid form without necessitating higher levels of carbon dioxide. Thus this weakens the conclusion.

Hope this helps.


Got it, thank you! I didn't realize the subtle difference between CO2 and Methane - I assumed they were the same thing.
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Re: About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink] New post   18 Jul 2020, 20:31
Now
    Premise:
    100% luminous
    More ice than water
    => Less heat
    Cause: less greenhouse gas
      Conclusion:
      Have less CO2

      3 billion years ago
      Premise
      80% luminous
      More water than ice
      => More heat
      Cause: more greenhouse gas
      Conclusion:
      Have more CO2

      Pre-think:
      But greenhouse gas contains some gas such as CO2 or methane, we only know the total greenhouse gas is more 3 billions years ago than today, we do not know about specific gas would decrease or increase
      What if the amount of methane in the Earth’s atmosphere 3 billion years ago was SO significantly more than that of today THAT the amount of methane could compensate for the amount of CO2 in the Earth’s atmosphere 3 billion years ago which was less than the the amount of CO2 today?
      Clearly, in this case, our conclusion is false.

      So, in all the choices, B is saying what we just thought
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      Re: About 3 billion years ago, the Sun was only 80 percent as luminous as [#permalink]
      18 Jul 2020, 20:31
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