|
The atmosphere (gaseous)
Description of the atmosphere
Composed of about 78% Nitrogen, 21% Oxygen, 1% Argon and traces of
carbon dioxide, water and other gases, the atmosphere is the least
dense and outermost of the earth's layers. Various thicknesses are given
for the atmosphere. In reality there is no clear upward boundary and the
atmosphere becomes less dense as we go outward. Somewhere near 100 miles
in height it is so thin that its atoms and molecules do not significantly
affect the orbit of satellites, so we can consider that a very approximate
but reasonable outer limit for the atmosphere. Relative to the hydrosphere
and lithosphere, the mass of the atmosphere is trivial and amounts to some
0.01% of the total mass of the planet.
Comparison of some planetary atmospheres
| Gas |
Earth |
Venus |
Mars |
Jupiter |
|
| Nitrogen N2 |
% 78.1 |
3.5 |
3.4 |
|
|
| Oxygen O2 |
21.0 |
|
|
|
|
| Argon Ar |
0.93 |
0.1 |
0.1 |
|
|
| Carbon dioxide CO2 |
0.036 |
96 |
96 |
|
|
| Neon Ne |
0.0018 |
|
|
|
|
| Helium He |
0.00052 |
|
|
18 |
|
| Hydrogen H2 |
0.000053 |
|
|
82 |
|
| Methane CH4 |
0.00017 |
|
|
|
|
| Krypton Kr |
0.00011 |
|
|
|
|
| Water (as vapor) H2O |
Variable 0.01 to 5 |
|
|
|
|
Origin of the atmosphere
The most likely origin of the atmosphere is from the outgassing
process, where countless volcanos have emitted volatiles (gases), including
water, over geological time. Nitrogen and carbon dioxide were the direct
product of outgassing. The most unique component of our atmosphere is oxygen,
created by billions of years of biological (photosynthetic) activity. Argon
is likely the decayed product of radioactive potassium. |
