Archean Atmosphere Flashcards
(26 cards)
what temp range do most organisms tolerate?
change of 10-20 Celsius
mesophile
organisms that like moderate temperatures
25 Celsius, give or take 10-20 degrees
psychrophiles
organisms that like cold temperatures
15 Celsius or lower
thermophile
organisms that like warm to hot temperatures
50 - 80 Celsius
hyperthermophile
organisms that like extremely hot temperatures
80-122 Celsius
Faint Young Sun paradox
stars get brighter over time
solar brightness in Archean
20-30% less bright than today
surface temperature in Archean, based on solar brightness
(assuming atmosphere composition equal to that of today)
265 K = below freezing
how do we know that the atmosphere in the Archean was not the same as today?
the surface was not frozen (known through geologic evidence - zircon oxygen isotopes, mica in gneiss)
solution to Faint Young Sun paradox
Greenhouse effect
Greenhouse Effect
heating of earth’s surface due to presence of an atmosphere that contains gases that absorb and emit infrared radiation
Greenhouse effect route
1 Sun shining on earth surface
2 some of suns’ infrared radiation is reflected off earth’s surface and atmospheric gases
3 some of sun’s infrared radiation is absorbed by earth’s surface, warming it
4 reflected radiation is absorbed and re-emitted by atmospheric gases in all directions, including back to the surface
albedo
diffuse reflection of light (heat) from light (energy) sources such as the Sun
- a specific form of reflectivity
low albedo
low reflected radiation
high albedo
high reflected radiation
Powerful greenhouse gases
water vapor
methane (CH4)
ammonia
nitrous oxide (N2O) (laughing gas)
water vapor in Archean atmosphere? How do we know?
not likely. water forms clouds which have high albedo, so most of the weak radiation from the young sun
Bad greenhouse gases
CO2
What does a high CO2 atmosphere cause and why
enhanced weathering
when disolved in water, it produces carbonic acid (H2CO3) which chemically weathers silicates, which produces clays and siderite (in paleosol over basalt)
Was Archean atmosphere high in CO2? How do we know?
probably not, but can’t be sure. No known evidence of Archean clays or siderite, but it may have still played a role by helping produce methane
Was methane in Archean atmosphere? How do we know?
Probably. It is a very powerful greenhouse gas, so it would not take much.
What abiotic sources would produce methane in the Archean?
Serpentinization producing H2 (at hydrothermal vents)
Fischer-Tropsch reactions H2 + CO2 -> CO
CO + H2 -> CH4 and water
might be enough CH4 to warm earth
What biotic sources would produce methane in the Archean?
~2.8 Ga - first evidence of methanogenesis,
not early enough to combat Faint Young Sun Paradox in early Archean, but present by late Archean
Was ammonia present in Archean atmosphere? How do we know?
Probably not.
UV radiation degrades ammonia
would need haze of organic aerosols to protect ammonia, which would create increased albedo because of how thick the haze would need to be and create anti-greenhouse effects
