What's In A Breath? The Supply Problem

Earth’s Atmosphere is Unique


Worlds Without atmospheres

          We take it for granted that when we breathe in (inhale), air is going to enter our lungs.    Go ahead, do it now. Breathe in. How nice to feel the air entering our lungs! However, breathing is useless if there is no air out there for us to breathe in. The next time you are visiting the Moon or the planet Mercury go ahead and take off your helmet. Take a deep breath. Quick! Put it back on! Did you notice that no air entered your lungs? In fact the opposite happened! When you opened your mouth to breath, the higher pressure air in your lungs was sucked out. Why?  Both Mercury and the Moon have no atmosphere with air molecules.  On these bodies there is a vacuum, no air at all.  It’s difficult to say what we would die from first - our tissues rapidly expanding because there is no air pressure pushing in on them, or lack of oxygen to the brain.

          How about our two closest neighbors, Venus and Mars?   Venus does have an atmosphere, but it is hostile to life.  Its atmosphere is too thick, being almost 100 times thicker than Earth’s.    When you opened your mouth to breathe so much air would rush in that your lungs would be crushed due to this intense pressure. Watch this video of atmospheric pressure crushing a can to help you realize what would happen to an unprotected body on Venus. On Mars, the red planet, we would have the opposite problem.  Its thin atmosphere has a pressure 100 times less than that of Earth.  At those low pressures, we would be doomed to the same fate as Mercury or the Moon. If we didn’t have a pressurized suit our bodies would inflate like a balloon.   "Within minutes the skin and organs would rupture, outgas, and produce a quick, painful death." says Chris Webster from Nasa’s Jet Propulsion Laboratory. (1) Not a pretty picture! Earth’s atmosphere has just the right amount of air molecules in it to support breathing, unlike Venus and Mars, which either have way too much air, or not enough air.

Planets and atmosphere.png

    Will any air do? Does it matter what types of air molecules we are breathing in? Air is air, right? Not by a long shot! Not only are the atmospheric pressures deadly on Venus and Mars, but the composition of the atmospheres is deadly also.  Both planets boast an atmosphere of roughly 95% carbon dioxide (CO2).  Scientists have determined that concentrations of CO­2 over 6% would make it impossible to eliminate the CO2 that builds up in our bodies and we would die from CO2 poisoning. (2) It’s hard to say what we would die from first!  There are around 30 common gases which are either elemental (like helium, hydrogen, nitrogen, oxygen, etc) or compounds (like carbon dioxide, methane, butane, etc). (2)  Of these 30 only one is capable of sustaining life – oxygen, and only Earth has an abundant supply.  When I consider Earth and its two closest neighbors, Venus and Mars, the story of Goldilocks and the Three Bears comes to mind.  Earth’s atmosphere is “just right” for keeping us alive!

The Precious 21% That Keeps Us Alive

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          A typical breath at rest brings in around ½ liter of air (500 mL) into our lungs.  That’s almost 11,000 Liters of air in one day, which is the volume of a cement-mixing truck.   Of the 500 mL approximately 105 mL are composed of oxygen molecules.    Of that 105 mL of oxygen, roughly 25%, a little over 26 mL, actually makes it into our bloodstream during each breath.  The weight of those 26 mL of oxygen in every breath is  0.0357g.  

That’s around 28 times lighter than a piece of paper (8.5 x 11 in) (2)  Multiply that by 21,600 breaths  and you get almost 800 grams of oxygen you remove from the air every day.   That’s 1.7 pounds of pure oxygen every day that your body must have to keep you alive, and that’s not accounting for when your body demands more oxygen because you are playing soccer, or working in the yard, or swimming or playing tag.  Only 1.7 pounds? Remember, this is air we’re talking about, which appears as though it weighs nothing at all!   The amount of daily oxygen your body uses on average is the approximate weight of a loaf of bread.

“That’s not that much”, you say.  Yet, when you factor in earth’s population, a whopping 6.4 million TONS of oxygen are being removed from the air every day!  How heavy is 6.4 million tons?  It is the approximate weight of the Great Pyramid of Giza. (3) This is the daily requirement to keep the world population alive! Now, are you worried about the Earth running out of oxygen? 


The daily supply of oxygen used by the world’s population is equal to the weight of the great pyramid

          No matter where you go on Earth, the air contains 21% oxygen.  The higher you travel in elevation above the Earth’s surface the air becomes increasingly thinner, however the percentage of oxygen stays constant at 21%(roughly 1 out of every 5 molecules is oxygen)  It’s been that way for all of recorded history.  If we’re removing over 12 million tons of oxygen from the atmosphere every day (we’ll double it due to animals) how does our oxygen level in the atmosphere remain at 21%? If oxygen is so necessary for us, why didn’t God give us an atmosphere with at least 50% oxygen, instead of only 21%?  Have you ever heard of the expression, “too much of a good thing?” Check out this video to see why. In the glass is 100% oxygen. What would it be like to try to fight a forest fire with this much oxygen?

          So, why is the atmosphere of Earth not depleted of oxygen?  The short answer is that God gave us plants with green leaves.  During the process of photosynthesis these seemingly simple leaves manufacture glucose by combining carbon dioxide removed from the air with sunlight and water.  That’s right – plants take air and turn it into food to feed the whole world!  A by-product of this reaction is oxygen.  One tree can produce roughly 260 pounds of oxygen per year, so it would take 2-3 trees to support 1 person with oxygen. (6)  Scientists believe that microscopic plants that float in the ocean (phytoplankton and seaweed) are responsible for over 1/2 of the oxygen created by plants. (Morsink, 2017)


plants not only sustain life on earth with food, but also give us breathable air

They use the energy from the sun to change carbon dioxide and water into food (glucose) and oxygen.

          A visual that helps me appreciate our wonderful atmosphere is looking at the earth from space you see our atmosphere as a thin blue ribbon which separates us from the blackness and emptiness of space.  This thin blue ribbon of air is what separates Earth from outer space and serves not only as a source of oxygen, but as a blanket to trap heat from the sun. 

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Questions to Consider:

  How did it happen that the planet we call home has a continual supply of 21% oxygen which is perfectly suited for its critical role in cellular respiration, which exists in exactly the right concentration in our atmosphere, along with processes in place which maintain this perfect level?   

Take another breath and think about the precious oxygen you just breathed in on its way to your cells where it will perform its life-saving work and extend your life for another 5-6 minutes.  God, thank You for Your wisdom and care in providing us our wonderful atmosphere!

We take our atmosphere for granted.  We shouldn’t.   God designed it to sustain life on planet Earth.