A1 - structure

layers

image: NOAA

all weather occurs in the first 10 km above the earth's surface
the atmospheric layers are characterised by the temperature profile
the troposphere has an unstable temperature as the temperature drops with height but hot air rises
the stratosphere has temperature increasing with height due to the ozone layer
the mesosphere, or the middle atmosphere is where the temperature drops to the loest values
the thermosphere is where the temperature increases rapidly due to molecular dissociation
it has a very large KE per molecule, but few molecules, so feels cold

image: A Wright, lecture notes

$N_{2}$ , $O_{2}$ and $A r$ are the permanent gases, as the ratios stay the same throughout the well-mixed part of the atmosphere, ie. the turbsophere, which includes the troposphere, stratosphere and mesosphere
variables gases include $H_{2} O$ , $C O_{2}$ and other trace gases

image: A Wright, lecture notes

the earth formed with no atmosphere
outgassing from volcanoes produced many gases (not $O_{2}$ )
water condensed in oceans, $H_{2}$ escaped, $C O_{2}$ was at 100 times present concentration so a larger greenhouse effect kept the atmosphere warmer for the young sun
emergence of life in the oceans produced $O_{2}$ and reduced $C O_{2}$ from photosynthesis
death of organisms and sedimentation led to sequestering of $C O_{2}$ in rocks
presence of $O_{2}$ enabled $O_{3}$ formation, giving UV protection

image: A Wright, lecture notes