How many generations

Here is a question that has puzzled me for a while.

We know the Earth is approx 6b years old and the Universe 15-16b years.
(Feel free to correct my figures I am too lazy to look them up!).

We know the elements that occur naturally on it and we also have theories suggesting the conditions that manufacture them from primorial (in a stellar sense) Hydrogen- eg Iron from nuclear fusion of a mainstream star. Heavier elements require Novae etc.

Can anyone hazzard a guess based on standard theory of stellar evolution on how many generations of stellar lives have gone into providing our current home?

I think I remember hearing that our sun is a third / fourth generation star, but couldn't be sure

I'm also under the impression that it's a fairly low number (certainly in terms of cosmology) -- but I don't have a specific figure.

-- Jeff.

Our Sun is definitely a second generation. As to it being any more is up for speculation based on the apparent known age of the Cosmos (13.7 billion years old). We know it is a second generation because of the make up of the other bodies around it. We have abundant elements such as heavy metals like iron, aluminium, titanium, and more in the planets and asteroids. These elements, in fact almost the periodic table above iron in weight (8 is it?) can really only be produced out of an atomic explosion like that of a supernova. So, the theory goes that the predecessor in our part of the galaxy became a supergiant, exploded when its fuel was exhausted (producing those heavy elements in the process), and from the nebula left over, our Sun formed. The rest, as they say, is history.

Seanie.

Parts of the presolar material have been preserved.
Their isotopic make up is very different from the solar value indicating that they were born in a range of presolar stars.
See:
en.wikipedia.org/wiki/Presolar_grains

As for how many "generations".
As Jeff said it's a very low number but it would depend on the masses of the precursor stars.
A lot of generations of supergiants have exploded.
On the other hand the first generation of brown dwarfs is still here and will be for tens of billions of years into the future.

Thanks to all who replied, especially Seanie and Petermark.

The reference you supplied to the Wiki entry on Pre Solar Grains was very interesting and lead me to the Nucleosynthesis entry which in summary goes something like:

300seconds after the Big Bang elements up to At No 3- Lithium form.

Stellar Fusion elements to At No 20 Calcium and At No 26 Iron

Supernovae and Fast Fusion Nickel At No 28.

Yes the suggestion that we may be on at least a second generation planet seems reasonable.