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Habitability (conditions for life's beginnings might be narrower than…
Habitability
conditions for life's beginnings might be narrower than conditions that allow it to continue
extremophiles
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extinction events
glaciation
impacts
large number of species extinct
Circumstellar habitable zone
Surface water
273 K - 373 K
Temp very important factor
balance of energy received and emitted
albedo
reflect star's energy away
habitable zone moves inward toward star
star's luminosity
main sequence stars increase during lifetime
~4 Ga ago Sun was 70% of current luminosity
habitable zone migrates away from star
greenhouse effect
carbon cycle
geochemical processes
modern modelling
Supposes Earthlike atmospheres
inner edge where photolysis of \(\text {H}_2\text {O}\) causes loss of H to space
outer edge
Greenhouse gases no longer able to compensate for decrease in stellar luminosity
Point where \(\text{CO}_2\) will condense in atmosphere
carbon thermostat
Adequate pressure
too low, sublimation
water phase diagram
changes in star's luminosity
continuous habitable zone
complex life (Earth-like)
Only past 500 Ma on Earth
stricter prerequisites
more stability
long term planetary heat source
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astrological conditions
impact rate
satellite is helpful
stellar conditions
stellar mass
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surface ocean
water cycle
plate tectonics
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erosion and chemical weathering of rocks
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temp regulation
moderately low \(\text{CO}_2\) and moderately high \(\text{O}_2\)
ozone layer production
UV radiation protection
physiology
dry land
microbial life
on Earth over 3 Ga
tolerates extremes better than more complex life
