How many generations

Makes you humble to think that not only do we live in a very big place...(the universe)...but that we are recycled carbon...second hand star dust.

When I done the OU course the literature said there was three generations of stars, I, II & III. All are classified on the amount of higher atomic elements. When the course was written they had still not discovered any first generation stars which would be primarily hydrogen and helium with trace amounts of lower atomic elements. Its been 4 years since I done the course so I may not 100% correct on this and I am open to correction.

Thanks Phoenix,
The classification you mention makes a lot of sense.

Yes I think that recently (in the last year) the Hubble telescope had a picture of some of the earliest stars. I think now I remember it was said at the time they were sure they were among the earliest stars known- obviously that was based on their spectral composition.

This pushes us out to possibly third generation material allright.

The reason I was so interested in the issue was because of the Drake equation and a post in the SETI thread which lowered the probability of SETI's success because the communications window between civilizations would be small. Developing civilizations would rely on RF communications for only a relatively short duration (on a cosmic scale) and hence the probability of two being the RF window simultaneouly was smaller (effectively the product of P1 by P2 where both P1 and P2 are considerably less than 1).

Now given that we may be 3rd generation material and the first generation phase didn't manufacture anything heavier than Lithium then at the very least the probability of civilizations elsewhere is possibly double that given by the Drake proposition.