Geoscience Reference
In-Depth Information
CHAPter 5
hat Controls Atmospheric Oxygen Concentrations?
Breathe in, breathe out, breathe in, breathe out. Nice and relaxed. We
each do this perhaps 20,000 times a day and we rarely give it any
thought. I think more about breathing, however, if I travel to Santa Fe,
New Mexico, with an elevation of 2100 meters (7200 ft.) above sea
level. Just after arrival, I'm panting after a flight of stairs, and during a
short run in the hills I huff and puff much more than usual. At this alti-
tude, atmospheric pressure is about 77% as great as at sea level, mean-
ing that for the same breath, we only pull in 77% as much oxygen. At
the top of the world, on the peak of Mount Everest in the Himalayas,
the elevation is a staggering 8848 meters (29,035 ft.), and here a lung-
full of air contains only about 31% as much oxygen as at sea level. Only
the best trained and best adapted can survive with so little oxygen, and
for only a short time at that. Most climbers make their final push up
the mountain with oxygen tanks. Some don't, and many die trying. The
top of Mount Everest clearly pushes the limits of what humans can
endure.
So, the amount of oxygen in the air does matter. Currently, the oxy-
gen content of the air is 21%, and we might rightfully ask why this
particular concentration.
1
We might also ask whether this concentra-
tion has changed over time. We will look at the history of atmospheric
oxygen in subsequent chapters, but here we will concern ourselves with
the more fundamental question of why there is oxygen in the atmo-
