This is an Earth systems science look at the cycling of atmospheric oxygen.
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PRELUDE TO
OXYSPHERE

    Atmospheric oxygen is taken for granted.  It is the design of the following essay, "Oxysphere" to emphasize oxygen's obvious importance and illuminate the complex and diverse mechanisms that control oxygen.  The cycling of atmospheric oxygen is an underappreciated player in the construction of the chemical web of life at Earth's surface.

ELIXIR OF LIFE

    Oxygen, in its gaseous form, O₂, is the elixir of life for organisms, such as ourselves, that are unable to synthesize their own food.  With each breath we take, the reactive power of oxygen provides fuel for our bodies.  Without any oxygen at all....the consequences are deadly.  At 10,000 feet above sea level, there is a third less air (a third less oxygen per breath) than at sea level.  Hikers at this altitude and above must allow their bodies to acclimate to the reduced amount of oxygen fuel.  Even with acclimation, the effects of high altitude oxygen deficiency manifests itself in a reduced ability for physical exertion and mental acuity.  The necessity for atmospheric oxygen is obvious although forgotten by humans who do not encounter a deficiency of it.  The level of atmospheric oxygen is a fairly delicate balance: a reduction of it by a few volume percent in air greatly diminishes the human blood's capacity to transport it.  An increase of it by a few volume percent greatly enhances the chances of dry matter to spontaneously combust.  The level of atmospheric oxygen at nearly 21 volume percent should not be taken for granted.
    Oxygen in the atmosphere also protects life with a shield against solar radiation.  Without the ozone shield, life would have to retreat beneath other protective layers, such as ocean water or rock.  Plant life would have to retreat from the atmospheric layer, greatly reducing the Earth's capability to resupply the atmosphere with oxygen.  Life has an incredible tenacity to survive....it can live at very low or very high pressures and/or temperatures and can also survive within a variety of chemical environments.  No life, however, can survive the onslaught of ultraviolet radiation that would bathe Earth's surface without the protective coating of oxygen molecules in the atmosphere.

A STRONG BOND

    Oxygen is extremely reactive.  It will chemically react with virtually any other substance.  The chemistry of the Earth's crust is a poignant example of this reactivity.  Consider the composition of the typical crust: the common igneous rock, granite.  It has been described as essentially a tight packing of oxygen atoms with some other atoms sprinkled in the spaces between.  To the surprise of many, in fact, all rocks have a much higher volume percentage of oxygen than does the air from which we draw breath.  The oxygen in rock is not in the gaseous form life can utilize for energy.  It is there, however, because oxygen bonds with anything it can....and does so naturally.  All the gaseous oxygen in the atmosphere would bond with other elements and eventually disappear were it not for the constant replenishment of the oxygen supply by plants.   Plants separate carbon and hydrogen from oxygen by harnessing energy from the sun.  Oxygen then permeates the atmosphere as a waste gas of photosynthesis.

OUT OF SIGHT

    Although oxygen is an obviously important constituent of the skies above, it seems to have escaped prevalence as a topic of scientific discourse.  Attention is more often given to other, less abundant gases of the atmosphere.  Many people, for example, are familiar with the steady rise in the levels of carbon dioxide in recent decades.  Rises in CO₂ levels in the geologic past and the present are believed linked to increases in global temperature; current research provides evidence in support of this hypothesis.  It alarms many to see the slow but steady rise in the CO₂ curve, a result of the burning of fossil fuels and other organic matter.  What gets little attention, however, is the decline in oxygen levels that the very same curve represents.  To visualize this decline, simply flip the CO₂ curve over.  As carbon is burned, oxygen is consumed.  Oxygen naturally tends to recombine with the carbon it was liberated from.  Oxygen began to accumulate in the atmosphere in appreciable amounts only because the associated carbon was buried in sediments away from oxygen's reach.  Humans have learned to extract some this stored carbon from Earth and to utilize the "fossil sun ray" energy that is released as it recombines with oxygen gas in a controlled burn.

WEB OF LIFE

    Despite the importance of oxygen gas, its chemical cycle is poorly understood.  Its cycle is tied to many other nutrient cycles and geologic processes in a complex and varied set of chemical reactions.  This makes oxygen an integral strand in the chemical web of life.  The chemical web of life on Earth is now being perturbed by humans in a variety of ways.  This is happening before an understanding of the web's design has been conceptualized.  You may be familiar with walking through a spider's web....it often remains unnoticed until it is destroyed.  Have you ever tried to repair a web once it is broken?  Do you think this is an inappropriate analogy for the complex chemical web of life on Earth?
    Human population has reached a size where it has driven Earth to a crossroads.  Small actions by each of us have dramatic impacts at the scale of Earth's human population.  The Earth has undergone many years developing and tailoring the chemical web of life.  The web has adjusted to many natural changes, some slow and some abrupt.  Life has suffered in the geologic past with slow and abrupt changes in the chemical cycling of nutrients.  The web as a whole has survived, even if some parts of it did not (such as the dinosaurs).  Humans are now perturbing strands of the web in numerous ways.  At this time, we cannot fully see the complexity of the chemical web of life....does this suggest we pretend it is not there?  How do we know we are breaking its strands, until the web collapses?

    The fact of the matter is that we may not ever fully understand the complex chemical web.  We may be able to see the major strands, however, before we bulldoze blindly through the web.  Oxygen is an essential strand that is drastically unappreciated.  The following essay, "Oxysphere", is an attempt to cultivate an appreciation for this forgotten player in the web of life.  It promotes an Earth systems science perspective, which is essential to the visualization of many global phenomena.  It is encouraged that the biogeochemical cycling of oxygen be used as a vehicle to promote Earth systems science.....it has breathtaking possibilities that can be understood by all.
    An ounce of prevention is worth a pound of cure.
    Protect the web.

    Ron Merritt Morris

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prelude, imagemap, introduction, atmos evolution, earth systems, reactivity, organic matters, phosphorus, oceanic processes,
photochemistry, fire, weathering, burial and tectonics, anthropogenic influence, glossary, references, quiz