The temperature range for life is very
very very narrow. Here are 2 goldilocks
zones:
1."Chemical reactions could have bound a greenhouse gas from
the atmosphere in minerals (carbon dioxide to carbonate
for instance). This could have led to a drop in the
average temp by just a few degrees, which could have
increased the size of the polar ice caps and thus the
fraction of sunlight reflected into space unused (termed
the albedo, i.e., whiteness of a planet) Postivive
feedback among a reduced energy intake, further drop in
temps, and further growth of the ice caps could have led
to a planet in the deep freeze, like our neighbor Mars.
Conversely, we could have ended up in a planetary oven,
considering that the luminosity of the Sun has increased by
some 40 % over the past 3 billion years. This would have
been more than enough to send us on an overheating feedback
loop, ending in a state comparable to that of our other
neighbor, Venus? (Life on the Edge, Gross)
2.But it just isn't the temperature that matters. Lovelock
has pointed out that it is also the type of sunlight.
"If the Sun were just dull red hot instead of blazing white,
and if the Earth were in a closer orbit and just as warm as
now, no life would be possible. the energy of light coming
from a dull red Sun is insufficient to break the chemical
bond between carbon and oxygen."
I'm beginning to think that life is so rare that ... the
odds are strongly against us being here now.
Comment?