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The figure above shows the historic composition, as percentages, of 03 Dec 2023, 01:56
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Dropdown 1: 2.4 Billion
Dropdown 2: Choose this one
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70% (01:47) correct 30% (01:47) wrong based on 563 sessions

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The figure above shows the historic composition, as percentages, of gases within the Earth's atmosphere. All gases depicted refer to their molecular forms, not to atoms of those elements within other compounds. (For example, oxygen refers to \(O_{2}\))
The table above shows the start dates for various time periods in Earth's geologic history.

3. Photosynthesis is a process that uses atmospheric carbon dioxide to produce sugar and atmospheric oxygen. The most likely point for the first photosynthesis to have occurred is years ago.

4. Please choose this drop-down as a Graphs question needs to have 2 .


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Dropdown 1: 2.4 Billion
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The figure above shows the historic composition, as percentages, of 09 May 2024, 12:59
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Please explain ques 3

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The figure above shows the historic composition, as percentages, of 17 May 2024, 17:39
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MartyMurray chetan2u KarishmaB , I thought it would be 2 billion years ago as at that time there would be both existence of atmospheric carbon di oxide and oxygen. Can you please explain why the answer is 2.4 billiion years ago ?
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The figure above shows the historic composition, as percentages, of 17 May 2024, 18:48
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The figure above shows the historic composition, as percentages, of gases within the Earth's atmosphere. All gases depicted refer to their molecular forms, not to atoms of those elements within other compounds. (For example, oxygen refers to \(O_{2}\))
 
Show more
­ Photosynthesis is a process that uses atmospheric carbon dioxide to produce sugar and atmospheric oxygen. The most likely point for the first photosynthesis to have occurred is _____ years ago.

The solution depends on only the above diagram, which gives start/existence of various gases in atmosphere.
We are looking for the time when oxygen started being formed in atmosphere with availability of carbon dioxide in air too.

The start of oxygen(yellow portion) being formed is between 2 billion years ago and 3 billion years ago, almost 2.4 billion years ago.
Of course, we cannot be sure that the presence of oxygen is an irrefutable evidence that photo synthesis started then. Photo synthesis could have started anytime in last 2.4 billion years. But we are looking at most likely point and that could be the start of presence of atmospheric oxygen.
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The figure above shows the historic composition, as percentages, of 17 May 2024, 18:54
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Well , just above the "2 billion " mark also we can see a big chunk of yellow ( indicating oxygen) and little bit green ( indicating CO2 ) .
Why not "2" then ?
I figured it out why it's not "2 billion years ago ". Because "2.4 billion years ago " is earlier than "2 billion years " ago. Since we are looking for "first photosynthesis to have occurred " , hence "2.4 billion years ago " will be more apt than "2 billion years" ago.chetan2u MartyMurray
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The figure above shows the historic composition, as percentages, of gases within the Earth's atmosphere. All gases depicted refer to their molecular forms, not to atoms of those elements within other compounds. (For example, oxygen refers to \(O_{2}\))
 
­ Photosynthesis is a process that uses atmospheric carbon dioxide to produce sugar and atmospheric oxygen. The most likely point for the first photosynthesis to have occurred is _____ years ago.

The solution depends on only the above diagram, which gives start/existence of various gases in atmosphere.
We are looking for the time when oxygen started being formed in atmosphere with availability of carbon dioxide in air too.

The start of oxygen(yellow portion) being formed is between 2 billion years ago and 3 billion years ago, almost 2.4 billion years ago.
Of course, we cannot be sure that the presence of oxygen is an irrefutable evidence that photo synthesis started then. Photo synthesis could have started anytime in last 2.4 billion years. But we are looking at most likely point and that could be the start of presence of atmospheric oxygen.
Show more

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