Lecture 6 Flashcards
The atmosphere of venus composition
Earths nearest neighbour
96.5% CO2, 3.5% N2 & trace gases
Venus pressure
92atm
Venus surface temperature and why
470 degrees celsius
Temp is high due to runaway greenhouse effect. Highly efficient infared trapping by the 97% CO2 atmosphere.
Two important reactions on venus
Photocleavage of CO2
CO2 –> CO + O
SO2 + O –> SO3
SO3 + H2O –> H2SO4
Sulfur oxidation cycle
SO2 –> SO + O
SO2 + O –> SO3
SO3 + H2O –> H2SO4
The atmosphere of Mars composition
96% CO2, 2% N2, 2% Ar, 0.15% O2 & tarce gases
Pressure on Mars
0.006atm, no strong magnetic field so many gases stripped away
Temperature on Mars
-125 degrees in winter +20 degrees in summer
What is unique about Mars
Permanent polar ice caps are covered in winter by CO2. CO2 falls like snow
Disequilibrium in Earths atmosphere
Fuel gases are constantly being replenished. Biological processes cause this such as interactions with biosphere and atmosphere.
O2 reacts with almost everything (H2, N2, CH4, S)
What is the evolution of earths atmosphere?
1) Original atmosphere: earth just formed (high temperatures). Hadean eon.
Composition–> H2, He, Trace CH4, NH3, H20
Source–> mainly H2 and He
Change –> H2 & He are light and fast moving, get driven off by solar wind and heat
2) Early atmosphere: cooling earth. Hadean and archean eon
Composition–> H2O, CO2, CH4, NH3, H2, He, CO
Source–> Earths formation from asteroids, volcanic activity, collisions w comets, photolysis
Change–> H2, He & heat leave to space. Ammonia & methane turned into N2, CO2 & C. Water is condensed to form oceans
3) Current atmosphere–> phanerozoic eon
Composition–> Permanent (78%N2, 21% O2, 0.93% Ar, 0.038% Co2 & traces)
Variable (0.4% H2O, Ch4, O3, SO2)
Source–> earth & human activities
Change–> Variable componentes vary with time and location but permanent do not
Miller and Urey Experiment 1953
simulated primitive earth conditions with abiotic synthesis of biochemicals. Used H2), NH3, H2, CH4 & an electric spark to model lightning. Several complex compounds were formed
Photosynthesis
Cyanobacteria produce O2
6CO2 + 6H20 + hv –> C6H12O6 + 6O2
How did O2 build up in earths atmosphere?
(3.85-2.45 Ga) Practically no O2
(2.45-1.85 Ga) O2 produced but absorbed into oceans & seabed rock
(1.85-0.85) O2 gases out of oceans but absorbed by land & formation of ozone layer
(0.85-now) O2 sinks are filled and gas can accumulate
Where is most O2 stored
only 10% of net oxygen is stored in atmosphere, and most is found in solid phase oxides & biogenically precipitated carbonates
