Evolution of the Atmosphere

Question 1

Faint Young Sun

Answer 1

The sun was 30% dimmer (Teff was smaller) when
Earth formed
• In the absence of atmospheric evolution, the early
earth would have been frozen over
• It wasn’t
• Implying… the atmosphere must have evolved
with time, containing more greenhouse gases (eg.,
CO2, CH4, NH3) in the past

Question 2

Gas concentration equation

Answer 2

d/dt[gas] (gas change in gas concentration at any given time)
=FSOURCE−FSINK
IF source> sink [gas] rises

Question 3

Why do atmospheres stick to planets?

Answer 3

GRAVITY (smaller planets have larger atm loss)

Question 4

Escape velocity calculation

Answer 4

set kinetic energy= potential energy

Question 5

Hydrogen escape to space

Answer 5

Earth has a hydrogen geocorona
Hydrogen escaping at 3kg/s
half from H2O photolysis, half from microbial CH4

Question 6

atmosphere sinks?

Answer 6

-Escape Process (Gravity, temperature..)
– Planetary surface (rain, particulates)
– Photochemistry (kinetic transformations)

Question 7

Sources of Gas in ATM?

Answer 7

Volcanic Activity:
Has been the same for most of Earth History
Heat generated through the radioactive decay of U, The and K
Fully predictable

Question 8

Atmosphere before life

Answer 8

• <10^-13 bar O2e very small trace! (from photolysis and escape of H) )
• ~0.8 bar inert N2
• ~10^-3 bar H2
• ~ 10^-2 CO2
  (Earth interior was slightly more radioactive, so a little more outgassing than present