Atmospheric oxygen levels Cambrian -> now

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!

 

This any good - it does at least have a list of references
http://www.pnas.org/cgi/reprint/103/29/10861.pdf

 

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.

 

:rofl: bwahaha !

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

 

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!

 

Try this

 

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.

 

A related question for any medical science buffs out there:

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?

 

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?

 

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.

 

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% O_{2 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.}