From: CurtAdams@aol.com
Date: Sat Sep 11 1999 - 13:04:18 MDT
In a message dated 9/11/99 9:41:07 AM Pacific Daylight Time,
bradbury@www.aeiveos.com writes:
> On Sat, 11 Sep 1999 hal@finney.org wrote:
>
> > But actually assembling some kind of self-replicating
> > system or cycle is still not well understood.
>
> Given that we get a stable crust ~4 billion years ago and life seems
> to appear at 3.86 billion years ago, that says that (a) it either
> came from space (panspermia); or (b) it is easy.
You're assuming that the development of life is progressive over a
multi-million year timeline. That's rather unlikely. In the absence
of life-like metabolic processes accumulated unformation would
decay over any substantial period.
Life may require a rare, fortuitous combination of circumstances.
In this case, intelligent civilizations would expect to see a delay
time randomnly and evenly distributed over [0,(possible duration of life)
-(time to develop to intelligent civilization)]. I've seen several estimates
that the world will become uninhabitable in about 1 billion years, based
on a) increases in insolation driving a greenhouse and b) recession of
the moon reducing the gyroscopic stabilization of the earth's axis of
rotation. If earth's life-sustaining span is 5 billion years, and it takes
4 billion to get from initial life to us, the we would expect to see the
origin of life as a random event in the first billion years. Seeing the event
at ~100 million is quite compatible with this.
I believe Robin Hanson has already addressed these issues of the timing
of the orgin of life vs. the probability of origin in more detail.
I could muster some arguments based on the speed with which metabolic
cycles must turn which indicate life might have to arise within *hours*
of appropriate circumstances developing, or you'll never see it at all.
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