The Origin of Carbon Dioxide

Planet Earth started out as a blob of plasma and over time developed a rocky carapace enveloped by an atmosphere now composed (on a dry basis) of 78.1% nitrogen, 20.9% oxygen and 0.9% argon, In addition, water vapor (H2O) comprises ~0.25% of Earths’ atmospheric mass.

Earths’ closest planetary neighbor, Mars, has an atmosphere composed of 96% CO2, 2.1% argon and 1.9% nitrogen. Earths’ other close planetary neighbor, Venus, has an atmosphere made up of 96.5% CO2 and 3.5% nitrogen.

From this it can be deduced that carbon dioxide is a product of planetary formation since there is no obvious sign of organic life on either Mars or Venus. The carbon on Earth must likewise have originated from non-organic sources, and the same can be said for oxygen.

In the current discussion on variability of Earths’ climate, the atmospheric components most often cited are: carbon dioxide, methane and water, the principle elements of these three compounds being carbon, hydrogen and oxygen. Hydrogen is the most abundant element in the universe, making up around 75% of its’ mass and on Earth it is one of the principle components of water (H2O).

The stratosphere of Saturn’s moon, Titan, has a composition of 98.4% nitrogen, 1.6% methane and 0.1%-0.2% hydrogen. Because methane condenses out at high altitudes, its abundance increases downwards and levels off at 4.9% at Titan’s surface. There are traces of other gaseous hydrocarbons such as ethane (C2H6), acetylene (C2H2), diacetylene (C4H2), methylacetylene (C3H4), propane (C3H8), carbon dioxide (CO2), carbon monoxide (CO), cyanogens (C2N2). Tar-like organic precipitates such as tholins may also be present (Wikipedia).

This observation poses the question of what came first: ‘the chicken or the egg’? Bacteria must have developed from methane and only subsequently did it develop the ability to create methane.

 

 

Element

/ planet

H

%

O

%

N

%

CO2

%

CH4

%

Ar

%

He

%

Na

%

Ices
Mercury ~22 ~42 ~6 ~29
Venus 3.5 96.5
Earth 20.9 78.1 0.04 180 ppb 0.9 H2O
Mars 0.14 1.9 96.0 2.1 CO2
Jupiter 89.8 0.3 10.2 NH3, H20

NH4SH

Saturn ~96 ~0.4 ~3 NH3, H20, NH4SH
Uranus ~83 2.3 ~15 NH3, H20, NH4SH CH4.5.75H2O
Neptune ~80 ~1.5 ~19 NH3, H20, NH4SH

CH4.5.75H2O

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