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 |
Bobburban's Blog 