# Atmospheric oxygen levels Cambrian -> now

Mentor

## Main Question or Discussion Point

I've googled quite a bit. Other than finding articles that require payment to view I have found nothing usable.

I need a source - possibly a table would be best - of estimated oxygen levels since the Cambrian. Thanks.

- Reason: the only text I have was out of print during the Eocene when nobody knew reliably about things like atmospheric oxygen levels. Well maybe not quite that old, but it may as well be.

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mgb_phys
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Don't have the reference in front of me but they were higher during a lot of the Paleozoic, one of the reasons for giant flying insects!

Mentor
I know about the general trends. I am apparently too stooopid to be able to google and get some kind of tabular result. Giant arachnids or insects can only happen when oxygen can diffuse to all of their body parts through spiracles. As $$O_2$$ leves drop the diffusion rate drops. and aniaml size does too.

I just want something maybe with references that says "during the Mississippian oxygen levels were X and this is how we know" It's Geology for sure, but I don't know Geology.

mgb_phys
Homework Helper
Mentor
Thank you, Pete, that is a great start.

LURCH
Just an aside; did anybody see Bill Maher host the "Earth to America" protest, (I mean, ah, "special") on TV? He started out with a comment about global warming and the US not signing the Kyoto protocalls, and he said that he read recently that the oxygen levels in Earth's atmosphere used to be 20%, and now it's down to about 6.

He was very alrmed by this.

vanesch
Staff Emeritus
Gold Member
Just an aside; did anybody see Bill Maher host the "Earth to America" protest, (I mean, ah, "special") on TV? He started out with a comment about global warming and the US not signing the Kyoto protocalls, and he said that he read recently that the oxygen levels in Earth's atmosphere used to be 20%, and now it's down to about 6.

:rofl: bwahaha !

Below about 16% oxygen, humans go in syncope...

mgb_phys
Homework Helper
I heard a similair one that oxygen levels had fallen to 1/10 of what they were before global warming. After all if CO2 has gone up, oxygen must have gone down!

Borek
Mentor
10 times you say.... it means there was 210% oxygen in the atmosphere earlier

I am sure I have a book with the oxygen level plot on the geological scale. And I am sure it is less than 3 meters from me. Unfortunatley I don't remember which one it is... But I am sure it is in Polish

Try this

Atmospheric oxygen shows a major broad late Paleozoic peak with a maximum value of about 30% O2 in the Permian, a secondary less-broad peak centered near the Silurian/Devonian boundary, variation between 15% and 20% O2 during the Cambrian and Ordovician, a very sharp drop from 30% to 15% O2 at the Permo-Triassic boundary, and a more-or less continuous rise in O2 from the late Triassic to the present.

Mentor
Oooh. Good one - thank you Andre.

You're welcome and remember, a scientific google is not google, but sciencedirect.com. Furthermore, I could get a hold of the PDF if you're interested.

Mentor
I'm a botanist - I can get references in most areas of Biology. The problem arises when I don't use terms I should in other discipline searches.

Thanks.

LURCH
A related question for any medical science buffs out there:
Atmospheric oxygen shows a major broad late Paleozoic peak with a maximum value of about 30% O2 in the Permian, a secondary less-broad peak centered near the Silurian/Devonian boundary, variation between 15% and 20% O2 during the Cambrian and Ordovician, a very sharp drop from 30% to 15% O2 at the Permo-Triassic boundary, and a more-or less continuous rise in O2 from the late Triassic to the present.
How would humans fair in an atmosphere that was 30% oxygen? I know people can breathe straight O2, but I've always heard that doing that for too long has an ill effect on the health (almost "burns up" the internal organs). If the atmo were 30% right now, and people had to breathe it all their loves, would there be any noticable effect on the health of the general population?

Borek
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Do you mean humans as of today, just transferred to the 30% oxygen atmosphere? Or do you mean how could humans adapt by the evolution? Not that I know answer, just the question sounds ambiguous.

In the Permian there were no humans, there were even no mammals yet, but it looks like other organisms had no problems with elevated oxygen level.

Borek
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LURCH
Now that I re-read it, you're right, Borek. I didn't state that very clearly.

I mean humans today. If O2 levels suddenly shot up to 30%, or a certain person or group of people found themselves living in a 30% environment on a long-term basis, would their health be effected? And how long would someone have to be on straight oxygen before their health would be adversely effected?

Yet another element, 30% of what? barometric pressure of one atmosphere or? How about the other main component, nitrogen? Lightning burns N2 to various NOx and has done so for billion years removing it from the atmosphere. Photosynthesis brings O2 back in the atmosphere for some sort of dynamic equilibrium. But what process is bringing N2 back in the atmosphere?

vanesch
Staff Emeritus
Gold Member
I mean humans today. If O2 levels suddenly shot up to 30%, or a certain person or group of people found themselves living in a 30% environment on a long-term basis, would their health be effected?
http://en.wikipedia.org/wiki/Oxygen_toxicity

I think that up to 0.5 bar partial pressure, oxygen doesn't pose a problem.

However, the main problem would be the higher potential for fire outbreaks, and the higher intensity of the fires.

Borek
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Oxygen toxicity aside, I wonder about long term effects. For example our skin is accustomed to the given level of oxygen. When the oxygen level goes up, it must change the chemistry of the external layers of skin, it must speed up oxidation proceses in epidermis. Could be it will just speed up peeling without any adverse effects, but it is just a wild guess.

LURCH
Yet another element, 30% of what? barometric pressure of one atmosphere or? How about the other main component, nitrogen? Lightning burns N2 to various NOx and has done so for billion years removing it from the atmosphere. Photosynthesis brings O2 back in the atmosphere for some sort of dynamic equilibrium. But what process is bringing N2 back in the atmosphere?
Good question, Andre. I believe that NOx life-expectancy in atmo is about a day or two (depending on altitude). IIRC; UV radiation knocks the N loose, and the O's form into Ozone at higher altitudes. I suppose the remaining N's find each other and bond back into N2, but that's just a guess on my part.

Vanesch, thanks for the lnk. I see from it that 50% O2 at normal atmoshperic pressures can cause inflamation of lung tissue after about 16 hrs. So, I'm betting that breathing a 30% mix 24/7 would do serious damage in less than a year.

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LURCH
I hope this isn't too far off topic (I think the OP's question has been thoroughly explored, anyway). Thinking about the interaction between CO2, NOx, UV (at high altitudes), and Ozone; I wonder if this interaction can be used to link the cycle of global climate change to the cycles of the hole in the ozone layer. Perhaps the opening in the ozone layer allows more UV to pass through the atmosphere, this UV gets trapped by greenhouse gases and converted to heat. However, the increase presence of UV triggers the production of more ozone, blocking UV and causing a temperature drop. Has anyone heard of this model before?

vanesch
Staff Emeritus
Gold Member
Vanesch -

Do you have a citation for that? Here's why [yes, I know it's gummint-ese, but they actually pay non-politicos to read the science sometimes]: