65,000,000 years ago, the atmospheric oxygen levels were around 35%, today, they're about 21%. What phenomena caused the drop? Was it simply a huge volcanic release of nitrogen?

 

Here's the main question. At what percentage would oxygen levels become detrimental to life (think animals and plants) as we know it? 40%? 50%? 60%? At what point would plants be starved of CO2? At what levels would high O2 levels begin to make nitrogen fixation difficult for plants?

 

Okay, let me narrow it down. Does anyone have a ballpark idea about what the highest O2 levels possible could be and still maintain a healthy ecological equilibrium?

65' date='000,000 years ago, the atmospheric oxygen levels were around 35%, today, they're about 21%. What phenomena caused the drop? Was it simply a huge volcanic release of nitrogen?

 

Here's the main question. At what percentage would oxygen levels become detrimental to life (think animals and plants) as we know it? 40%? 50%? 60%? At what point would plants be starved of CO2? At what levels would high O2 levels begin to make nitrogen fixation difficult for plants?

 

Okay, let me narrow it down. Does anyone have a ballpark idea about what the highest O2 levels possible could be and still maintain a healthy ecological equilibrium?[/quote']

Supposedly, the mere fact of surpassing the barrier of 21% would be very damaging, according to this muslim site

http://albalagh.net/general/earth_planet.shtml

"If the oxygen percentage in the atmosphere were greater than 21%, the cells in our body would soon start to suffer great damages. The vegetation and hydrocarbon molecules needed for life would also be destroyed"

Again, I don't claim any expertise in this field, so will be you who decides if the info in that page is accurate or not

Regards