Re: Our rocky solar system may be rare

Robert J. Bradbury (
Sat, 11 Sep 1999 00:44:32 -0700 (PDT)

On Sat, 11 Sep 1999 wrote:

> I am betting that Technology -Building life is extremely rare. Not because
> they decide to polute or to huff nukes or to nano-crap on themselves. I am
> suspecting that the initial conditions that promote tool users are
> vanishingly rare.

But humans aren't the only tool users! Birds and apes and dolphins all naturally invent or can be taught to use tools. You can't say "technology building" life is rare when the foundations of it care found in multiple species. Developing tools has a survival advantage, so no matter how long it takes to accidentally develop, once it does, it will tend to survive and prosper.

> Items such as Yellow stable stars,

We have 10's of millions G-class stars. We have even more smaller, K/M stars, that live longer and can support life (with a somewhat reduced habitable zone).

> a local sizable moon,

Why, for tides? That argument is over-rated. An ocean is an energy poor environment, sooner or later things will move out of it onto land because there is more energy available and the niche is uncolonized.

> a huge gas giant to slurp up the comets and asteroids,

I mentioned to Jill Tarter at the bioastronomy conference that the lack of a gas giant could *speed up* evolution. More frequent extinctions could select for the species that can see the comets coming and do something about them! She indicated that she was aware of the argument and seemed to be withholding judgement due to a lack of information. We don't know enough to know whether our development was "slowed" by our over-protective system.

> convection and subduction between an early planets surface
> and its mantle,

If the planet is in the Mars/Earth/Venus size range or subject to tidal forces (like Io), you are likely to get this. The length of time it remans active will depend on the size of the planet or the duration of the tidal forces.

> the right climate, etc.

This seems to presume you need what "liquid water"? How about liquid ammonia? Or liquid "tar"? So long as you are in a "habitable zone" for the type of life that can be evolved in that zone, the climate doesn't affect things much other than to perhaps slow down or accelerate the rate of change.

> Also I contend, that 12-20 billion years is a subjective view
> on what it takes to bring forth intense self awareness.

Of course it is since we don't have any other examples.

But two factors weigh against you:
(1) the very large number of stars (10's of millions) that

have habitable zones and live 5-20 billion years. (2) the fact that the consensus estimate is for a universe at

least 7.5 billion years older than our system.

For intelligent technological civilizations not to have evolved, you would have to keep knocking intermediate states of life back into the dust again and again and again -- faster than it can possibly get back up. And you would have to do this in all those millions of systems for billions of years. Difficult, VERY difficult.

> We may be the first beings in the Local Group to attain this
> awareness.

Perhaps, but unlikely.

> We are set (I suspect) against the after-glow of creation.
> Flip a coin.

You can't just flip one, you have to flip millions over and over and pray that *none* of them come up heads.