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 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.