<p>The oxygen in the atmosphere was produced by cyanobacteria during the <a href="https://en.wikipedia.org/wiki/Great_Oxygenation_Event" rel="noreferrer">Great Oyxgenation Event</a>, around 2.3 billion years ago. Cyanobacteria produced &amp; still, produces, to a lesser extent, oxygen by photosynthesis. Plants did not exist during the Great Oxygenation Event, but these day plants replenish atmospheric oxygen by removing carbon dioxide by photosysnthesis, like cyanobacteria. According to David Biello, <a href="http://www.scientificamerican.com/article/origin-of-oxygen-in-atmosphere/" rel="noreferrer">The Origin of Oxygen in the Earth's Atmosphere</a> the production of oxygen by cyanobacteria during the Great Oxygenation Event took one billion years.</p>

<p>During the Carboniferous period, about 350 million years ago, the amount of oxygen in the atmosphere increased to 30% because the rate of burial of organic matter prevented it from reacting with atmospheric oxygen, <a href="http://newworlds.colorado.edu/search/o2.htm" rel="noreferrer">History &amp; Significance of Oxygen in the Atmosphere</a></p>

<p>According to Wallace S. Broecker our atmospheric oxygen supplies are vast: </p>

<blockquote>
  <p>Simply put, our atmosphere is endowed with such an enormous reserve of this gas that even if we were to burn all our fossil fuel reserves, all our trees, and all the organic matter stored in soils, we would use up only a few percent of the available $\ce{O2}$. No matter how foolishly we treat our environmental heritage, we simply don't have the capacity to put more than a small dent in our $\ce{O2}$ supply. </p>
</blockquote>

<p>From <a href="http://www.columbia.edu/cu/21stC/issue-2.1/broecker.htm" rel="noreferrer">Atmospheric oxygen - Broecker</a></p>

CC BY-SA 3.0
2015-01-30T15:15:26.827Z
Broeker also says, "the Earth's plants produce through photosynthesis an amount of O2 equal to that of the atmosphere in about 2,000 years". Of course they're simultaneously absorbing oxygen, that's why it's called a cycle and why removing them wouldn't mean we asphyxiate in 2000 years. But it's sometimes significant what speed the cycle operates relative to the reservoir. It's not like we're still coasting on a 2.3 billion-year-old, or even 350-million-year-old, store.
Steve Jessop
CC BY-SA 3.0
2015-01-30T17:56:19.100Z
How could Cyanobacteria produce that much oxygen? Why hasn't such production continued?
Stan Shunpike
CC BY-SA 3.0
2015-01-30T19:14:52.923Z
I would challenge the idea that the oxygen present in the atmosphere TODAY was produced by cyanobacteria several billion years ago.  Today's oxygen is produced by plants, and cycles through in about 4500 years.  (Per Wikipedia, anyway: https://en.wikipedia.org/wiki/Oxygen_cycle#Capacities_and_fluxes )
jamesqf
CC BY-SA 3.0
2015-01-30T20:21:04.993Z
@jamesqf Suppose you are correct. Then what relevance is the Great Oxygenation Event have for today's atmosphere? In other words, that would mean today's plants would be producing all the oxygen, right?
Stan Shunpike
CC BY-SA 3.0
2015-01-30T21:05:43.563Z
@Stan Shunpike: Yes.  Or to be more precise, they are driving the Oxygen Cycle (see the Wikipedia link) that keeps the atmospheric O2 concentration at about 20%.  Really simplifying the process, animals breathe O2, which combines with food to produce growth & movement.  The combination produces CO2, which gets converted back to O2 and biomass by plants.
jamesqf
CC BY-SA 3.0
2015-01-30T12:19:24.523Z
2015-01-30T12:21:39.033Z
2015-01-30T12:21:39.033Z
Fred
<p>Yes today’s photosynthesis is occurring but so is the oxidation of the carbon based plant material when they decay and consumed. 
In order to have a surplus molecular Oxygen quantity the products of photosynthesis cannot undergo oxidation. 
Our biggest threat is the diminishing of molecular Oxygen because that is what absorbs UV energy and releases it as light before the UV can reach the Earth’s surface and become light and heat where it can cause the most damage with retainment of destructive forces at the earths surface. 
Remember that petroleum and coal are the products of photosynthesis and we are consuming them at an exponential rate. </p>

CC BY-SA 4.0
2019-02-25T12:38:03.600Z
"Molecular oxygen" is commonly understood to be O₂. The form of oxygen that absorbs UV radiation is ozone, O₃.
Gimelist
CC BY-SA 4.0
2019-02-24T16:27:36.553Z
2019-02-24T16:27:36.553Z
Mk green
<p>Depends on your definition of "plants", if you simply mean organisms using chloroplastic photosynthesis which is the most basic definition then the answer is almost all of it. If you want to know how much of the oxygen we breath is from land plants like trees and grasses the answer is roughly 55% annually with 45% being from phytoplankton blooms with trace amounts generated by UV radiation acting on water and certain nitrogen oxides in the upper atmosphere. </p>

<p>It's hard to say what a plant minimum for mammalian survival would look like because the availability of atmospheric oxygen would effect the interactions of that oxygen with the biosphere, hydrosphere, and lithosphere. Also which mammals? Mole-rats need significantly less oxygen per kilogram than humans which need less than mice.</p>

CC BY-SA 3.0
2017-08-14T14:10:12.253Z
2017-08-14T14:10:12.253Z
Ash
<p>More trees have been planted than ever before with the Arbor Society. Oxygen is the biproduce as plants need carbon dioxide to live(photosynthasis.) Volcanic, platelet fishers and forest fires account for natural carbon dioxide in the atmosphere. Man made fossil fuels are only a small % of carbon dioxide. They do contribute to the % level though.</p>

CC BY-SA 4.0
2020-12-20T11:43:19.547Z
Welcome to ES.SE. Unfortunately this doesn't really answer the question asking about the _amount_ of O2 in the atmosphere.  Also, I wouldn't call the 30% of CO2 in the atmosphere attributed to human activities (265 of 860 GtC) a small %.
Deditos
CC BY-SA 4.0
2020-12-19T20:47:52.833Z
2020-12-19T20:47:52.833Z
George Gardner
<p>I know plants form a critical part of the earth's biosphere, including molecular oxygen production. Molecular oxygen makes up <a href="http://www.space.com/17683-earth-atmosphere.html" rel="nofollow noreferrer">~20%</a> of our atmosphere.  How much of the earth's molecular oxygen in the atmosphere is due to plants? Is there a minimal level of plant life necessary to maintain levels of oxygen so that land mammals can live? Also, are land plants mostly important or are underwater plants a significant source of atmospheric oxygen?</p>

CC BY-SA 3.0
2015-01-30T12:45:17.300Z
The answer to the question is none. Earth's oxygen comes from the stars mostly. Now, it is clear that you are asking about Earth's oxygen in a molecular form. I think the question needs a good edit to clarify
arkaia
<atmosphere><biomass><biogeochemistry>
How much of earth's molecular oxygen in the atmosphere is due to plants?
Stan Shunpike
# How much of earth's molecular oxygen in the atmosphere is due to plants?

(Asked by: username_0 on 2015-01-30)

I know plants form a critical part of the earth's biosphere, including molecular oxygen production. Molecular oxygen makes up [~20%](http://www.space.com/17683-earth-atmosphere.html) of our atmosphere. How much of the earth's molecular oxygen in the atmosphere is due to plants? Is there a minimal level of plant life necessary to maintain levels of oxygen so that land mammals can live? Also, are land plants mostly important or are underwater plants a significant source of atmospheric oxygen?

**Tags:** atmosphere, biomass, biogeochemistry

> **Comments:**
> **username_1**: The answer to the question is none. Earth's oxygen comes from the stars mostly. Now, it is clear that you are asking about Earth's oxygen in a molecular form. I think the question needs a good edit to clarify  

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## 4 answers

### Answer by username_2 on 2015-01-30. Score: 8

The oxygen in the atmosphere was produced by cyanobacteria during the [Great Oyxgenation Event](https://en.wikipedia.org/wiki/Great_Oxygenation_Event), around 2.3 billion years ago. Cyanobacteria produced & still, produces, to a lesser extent, oxygen by photosynthesis. Plants did not exist during the Great Oxygenation Event, but these day plants replenish atmospheric oxygen by removing carbon dioxide by photosysnthesis, like cyanobacteria. According to David Biello, [The Origin of Oxygen in the Earth's Atmosphere](http://www.scientificamerican.com/article/origin-of-oxygen-in-atmosphere/) the production of oxygen by cyanobacteria during the Great Oxygenation Event took one billion years.

During the Carboniferous period, about 350 million years ago, the amount of oxygen in the atmosphere increased to 30% because the rate of burial of organic matter prevented it from reacting with atmospheric oxygen, [History & Significance of Oxygen in the Atmosphere](http://newworlds.colorado.edu/search/o2.htm)

According to Wallace S. Broecker our atmospheric oxygen supplies are vast:

> Simply put, our atmosphere is endowed with such an enormous reserve of this gas that even if we were to burn all our fossil fuel reserves, all our trees, and all the organic matter stored in soils, we would use up only a few percent of the available $\ce{O2}$. No matter how foolishly we treat our environmental heritage, we simply don't have the capacity to put more than a small dent in our $\ce{O2}$ supply.

From [Atmospheric oxygen - Broecker](http://www.columbia.edu/cu/21stC/issue-2.1/broecker.htm)

> **Comments:**
> **username_3**: Broeker also says, "the Earth's plants produce through photosynthesis an amount of O2 equal to that of the atmosphere in about 2,000 years". Of course they're simultaneously absorbing oxygen, that's why it's called a cycle and why removing them wouldn't mean we asphyxiate in 2000 years. But it's sometimes significant what speed the cycle operates relative to the reservoir. It's not like we're still coasting on a 2.3 billion-year-old, or even 350-million-year-old, store.  
> **username_0**: How could Cyanobacteria produce that much oxygen? Why hasn't such production continued?  
> **username_4**: I would challenge the idea that the oxygen present in the atmosphere TODAY was produced by cyanobacteria several billion years ago.  Today's oxygen is produced by plants, and cycles through in about 4500 years.  (Per Wikipedia, anyway: https://en.wikipedia.org/wiki/Oxygen_cycle#Capacities_and_fluxes )  
> **username_0**: @username_4 Suppose you are correct. Then what relevance is the Great Oxygenation Event have for today's atmosphere? In other words, that would mean today's plants would be producing all the oxygen, right?  
> **username_4**: @username_0: Yes.  Or to be more precise, they are driving the Oxygen Cycle (see the Wikipedia link) that keeps the atmospheric O2 concentration at about 20%.  Really simplifying the process, animals breathe O2, which combines with food to produce growth & movement.  The combination produces CO2, which gets converted back to O2 and biomass by plants.  

---

### Answer by username_5 on 2019-02-24. Score: 1

Yes today’s photosynthesis is occurring but so is the oxidation of the carbon based plant material when they decay and consumed.
In order to have a surplus molecular Oxygen quantity the products of photosynthesis cannot undergo oxidation.
Our biggest threat is the diminishing of molecular Oxygen because that is what absorbs UV energy and releases it as light before the UV can reach the Earth’s surface and become light and heat where it can cause the most damage with retainment of destructive forces at the earths surface.
Remember that petroleum and coal are the products of photosynthesis and we are consuming them at an exponential rate.

> **Comments:**
> **username_6**: "Molecular oxygen" is commonly understood to be O₂. The form of oxygen that absorbs UV radiation is ozone, O₃.  

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### Answer by username_7 on 2017-08-14. Score: 0

Depends on your definition of "plants", if you simply mean organisms using chloroplastic photosynthesis which is the most basic definition then the answer is almost all of it. If you want to know how much of the oxygen we breath is from land plants like trees and grasses the answer is roughly 55% annually with 45% being from phytoplankton blooms with trace amounts generated by UV radiation acting on water and certain nitrogen oxides in the upper atmosphere.

It's hard to say what a plant minimum for mammalian survival would look like because the availability of atmospheric oxygen would effect the interactions of that oxygen with the biosphere, hydrosphere, and lithosphere. Also which mammals? Mole-rats need significantly less oxygen per kilogram than humans which need less than mice.


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### Answer by username_8 on 2020-12-19. Score: 0

More trees have been planted than ever before with the Arbor Society. Oxygen is the biproduce as plants need carbon dioxide to live(photosynthasis.) Volcanic, platelet fishers and forest fires account for natural carbon dioxide in the atmosphere. Man made fossil fuels are only a small % of carbon dioxide. They do contribute to the % level though.

> **Comments:**
> **username_9**: Welcome to ES.SE. Unfortunately this doesn't really answer the question asking about the _amount_ of O2 in the atmosphere.  Also, I wouldn't call the 30% of CO2 in the atmosphere attributed to human activities (265 of 860 GtC) a small %.  

---

