There are two possible -- and possibly
contradictory -- implications of the faint early
Sun paradox and the relevant geologic evidence.
Jim Kasting (Penn State) has proposed that the early
Earth (and also the early Mars) had thick atmospheres
of CO2 (several hundred times as much atmospheric CO2
as we have now). This allows greenhouse warming of the
planet -- we will talk about the greenhouse effect shortly.
What effect does having a thick atmosphere
of CO2 have on the origin of life? And how does this
play into the carbon cycle on the early Earth compared
to today?
Note that Chyba et al. also found that a thick (CO2)
atmosphere is needed to deliver organic molecules to
the early Earth.
We also know from geological evidence that atmospheric
oxygen suddenly became very important around
2 billion years ago (we'll talk about that shortly).
So two questions
are these: What happened to the atmospheric
CO2, and where did all this atmospheric oxygen (O2)
come from?