Oxygen in Atmosphere in Historical Decline?

Being a "pretty good" Internet researcher, I have been having a hard time answering the following to my satisfaction:

What was the percentage of oxygen in our atmosphere 100 years ago? And:
What is it today?

Maybe the CO2 issue is not the whole story. Anyone with internet skills surpassing mine (or access to very old textbooks in college chemistry) please help out here!

A very good point Noumenon .But any effect on the amount of oxygen hasent had time to show its self yet as the margirty of earths oxygen comes from a type of phytoPlankton. (looked it up)
In conclusion the oxygen will remain realtively the same untill a large drop of these ocean plants . Ps All land plants produce oxygen ONLY during the day and obsurbe oxygen at night the net gain is near 0 .
The point being you could pave ever bite of dry land and the o2 wouldnot drop much .
But you kill the oceans even if the land is green we still die .
Pss we are killing the oceans so eventuly a drop in o2 can happen but even with the oceans compleatly dead it will take thousands of years to get to the point were you cant breath .
pss the air is 79% nitrogen 20% oxygen and 1% other.
and we would be just fine at 10% oxygen and start dieng once it gets below that.

[edit on 15-4-2005 by Simcity4Rushour]

Any lab techs out there that can tell us to within 2 decimal points the percentage of O2 in the air TODAY?

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Ice cores contain gases from the past.

They are used to tell what the composition of the atmosphere was in the past.

I haven't thought about changing oxygen levels. If it is significantly changing that would be very big news.
I would guess if any credible evidence to that effect showed up someone would probably say something.

If you do hear anything along those lines i [and probably anyone/thing who breathes] would be interested in hearing about it.
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