<p>The question rather assumes that we know what the atmosphere of Earth was like before the origin of life.
We don't.
Planetary scientists vary between an N<sub>2</sub>-CO<sub>2</sub>-CH<sub>4</sub>-Ar (in descending concentration), a H<sub>2</sub>-CH<sub>4</sub>-CO<sub>2</sub>-Ar atmosphere, and various other models. It is a very unsettled point. Different scientists (and teams) have diverging, strongly held, poorly evidenced opinions.</p>
<p>If you're &quot;world-building&quot; for an SF novel, pick the atmosphere you want for your novel and use that. There is no better reason to prefer one model over another.</p>
<p>One thing we do know : in the Archean (say, 3000 million years ago) minerals which can be attacked by even small traces of oxygen were present as water-transported sediment grains. So the [O] (&quot;concentration of O<sub>2</sub>&quot;) in the atmosphere was very low - far below 1% of current levels. So your spaceman would need at least an oxygen mask, if not a complete pressure suit.</p>

CC BY-SA 4.0
2024-06-17T13:20:14.797Z
2024-06-18T01:36:43.367Z
2024-06-18T01:36:43.367Z
Rockdoctor
<p>On Earth, it was life that absorbed the CO2 from the atmosphere. But we cannot tell that without life there wouldn't be any other global chemical process that would do the same thing, or something absolutely different that we even cannot imagine. The global processes consist of many reactions and we cannot predict which of them would play the main roles, and in what sequence. Especially while we don't know the exact state of the ancient atmosphere. The explanation postfactum, as in the article mentioned by You, is NOT the real science, let's not forget it. It is merely pre-science. And you are trying to ask the question about the prediction of processes due to the start state - it is a serious question that only a real science can answer.</p>
<p>The conditions on Earth and Venus were very different from the times of the Gaian impact, our atmosphere was a thousand times weaker. There is no evidence that so much weaker atmosphere would have the same evolution. We could have an atmosphere evolution similar to Mars or something specific to our planet. Or we could be a snowball like Europe. Don't forget, that some atmospheres can have a negative greenhouse effect.</p>

CC BY-SA 4.0
2024-06-17T15:17:30.987Z
The ocean absorbed the CO2. Life played a part, reducing the concentration by forming carbonate shells and later photosynthesis, causing the ocean to absorb more CO2 out of the atmosphere,  but form enough limestone abiotically (in the presence of dissolved magnesium and calcium, with temperature and pressure variations) and you might get the same mechanism sucking all the CO2 out of the atmosphere during the Precambrian.
Spencer
CC BY-SA 4.0
2024-06-20T10:26:15.823Z
@Spencer It is exactly what I am talking about in the post's first paragraph.
Gangnus
CC BY-SA 4.0
2024-01-14T21:52:57.303Z
2024-01-14T22:04:36.063Z
2024-01-14T22:04:36.063Z
Gangnus
<p>Without Photosynthetic bacteria to convert CO2 to Oxygen, It'd still be &quot;Primordial&quot;
Earth' ancient atmosphere <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944365/" rel="nofollow noreferrer">was</a> Nitrogen, Carbon dioxide, Ammonia, Methane, Water vapor</p>

CC BY-SA 4.0
2024-06-15T22:49:18.923Z
2024-06-15T22:49:18.923Z
LazyReader
<p>I'm also interested in understanding the mechanisms that affect what happens to the various gases in the atmosphere over time. That is, do they get locked away in minerals, stay in the atmosphere, or get blown off into space by the solar wind? How are these mechanisms affected by the planet's mass, distance from the sun, rate of rotation, size and distance of the moon, etc. in the absence of life?</p>
<p>For example, <a href="https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle#:%7E:text=The%20carbonate%E2%80%93silicate%20geochemical%20cycle,rocks%20by%20metamorphism%20and%20volcanism." rel="nofollow noreferrer">according to Wikipedia's article on the Carbonate–silicate cycle</a>, Venus lost its water by photodissociation and hydrogen escape, then Venus stopped removing carbon dioxide from its atmosphere, began instead to build it up, and experienced a runaway greenhouse effect. Is life the reason why this didn't also happen on Earth, or is there a different reason?</p>

CC BY-SA 4.0
2024-06-16T02:51:35.870Z
Plate tectonics also has a large impact on earths atmosphere.
John
<atmosphere><atmosphere-modelling><sedimentology><carbon-cycle><greenhouse-gases>
What would Earth's atmosphere be like today if life had never existed on it?
phil1008
# What would Earth's atmosphere be like today if life had never existed on it?

(Asked by: username_0 on 2024-01-09)

I'm also interested in understanding the mechanisms that affect what happens to the various gases in the atmosphere over time. That is, do they get locked away in minerals, stay in the atmosphere, or get blown off into space by the solar wind? How are these mechanisms affected by the planet's mass, distance from the sun, rate of rotation, size and distance of the moon, etc. in the absence of life?

For example, [according to Wikipedia's article on the Carbonate–silicate cycle](https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle#:%7E:text=The%20carbonate%E2%80%93silicate%20geochemical%20cycle,rocks%20by%20metamorphism%20and%20volcanism.), Venus lost its water by photodissociation and hydrogen escape, then Venus stopped removing carbon dioxide from its atmosphere, began instead to build it up, and experienced a runaway greenhouse effect. Is life the reason why this didn't also happen on Earth, or is there a different reason?

**Tags:** atmosphere, atmosphere-modelling, sedimentology, carbon-cycle, greenhouse-gases

> **Comments:**
> **username_1**: Plate tectonics also has a large impact on earths atmosphere.  

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## 3 answers

### Answer by username_2 on 2024-06-17. Score: 3

The question rather assumes that we know what the atmosphere of Earth was like before the origin of life.
We don't.
Planetary scientists vary between an N2-CO2-CH4-Ar (in descending concentration), a H2-CH4-CO2-Ar atmosphere, and various other models. It is a very unsettled point. Different scientists (and teams) have diverging, strongly held, poorly evidenced opinions.

If you're "world-building" for an SF novel, pick the atmosphere you want for your novel and use that. There is no better reason to prefer one model over another.

One thing we do know : in the Archean (say, 3000 million years ago) minerals which can be attacked by even small traces of oxygen were present as water-transported sediment grains. So the [O] ("concentration of O2") in the atmosphere was very low - far below 1% of current levels. So your spaceman would need at least an oxygen mask, if not a complete pressure suit.


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### Answer by username_3 on 2024-01-14. Score: 0

On Earth, it was life that absorbed the CO2 from the atmosphere. But we cannot tell that without life there wouldn't be any other global chemical process that would do the same thing, or something absolutely different that we even cannot imagine. The global processes consist of many reactions and we cannot predict which of them would play the main roles, and in what sequence. Especially while we don't know the exact state of the ancient atmosphere. The explanation postfactum, as in the article mentioned by You, is NOT the real science, let's not forget it. It is merely pre-science. And you are trying to ask the question about the prediction of processes due to the start state - it is a serious question that only a real science can answer.

The conditions on Earth and Venus were very different from the times of the Gaian impact, our atmosphere was a thousand times weaker. There is no evidence that so much weaker atmosphere would have the same evolution. We could have an atmosphere evolution similar to Mars or something specific to our planet. Or we could be a snowball like Europe. Don't forget, that some atmospheres can have a negative greenhouse effect.

> **Comments:**
> **username_4**: The ocean absorbed the CO2. Life played a part, reducing the concentration by forming carbonate shells and later photosynthesis, causing the ocean to absorb more CO2 out of the atmosphere,  but form enough limestone abiotically (in the presence of dissolved magnesium and calcium, with temperature and pressure variations) and you might get the same mechanism sucking all the CO2 out of the atmosphere during the Precambrian.  
> **username_3**: @username_4 It is exactly what I am talking about in the post's first paragraph.  

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### Answer by username_5 on 2024-06-15. Score: 0

Without Photosynthetic bacteria to convert CO2 to Oxygen, It'd still be "Primordial"
Earth' ancient atmosphere [was](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944365/) Nitrogen, Carbon dioxide, Ammonia, Methane, Water vapor


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