If life is normal... (Crossposted)

[Note Followup-To:.]

"JL" == John Leonard writes:

JL It occurred to me the other evening, that the universe is supposed
JL to be ~14 billion years old. Life on Earth is supposed to be ~3.5
JL billion years old. Human life is 1 million years.
[...]
JL It seems that one of the results of Scientific progress is to
JL disabuse us of an infantile concept of ourselves as being the
JL center of everything and replace it with another conception in
JL which we are merely average.

JL If this interpretation is correct then given the age of the
JL Universe and the variation about an average (say, our Earth's age)
JL that would be expected (...), what possibilities might exist
JL regarding life in our Universe? In other words if we were to
JL assume that we are not unique what might be the actual age of
JL life? Is it reasonable to guess, merely on the basis of our
JL (...) averageness that it could be much greater than our own?

Yes. There has been a fair amount of speculation about this point.
The difficulty is that, with only one sample to study (us), it's
difficult to reach any definitive conclusions.

There seems to be widespread agreement among at least astronomers that
life originates easily and is widespread. (The ubiquity of
*intelligent* life is far less agreed-upon.)

Livio (1999, URL:
http://adsabs.harvard.edu/cgi-bin/np...pJ...511..429L
argues that it actually takes some time for the amount of "metals"
(i.e., elements heavier than helium) to build up to a point at which
life can arise. Lineweaver & Davis (2002,
URL:http://xxx.lanl.gov/abs/astro-ph/0209385) try to do a
statistical analysis, but, again, they are hampered by the fact that
they have a sample of one.

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