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(meteorobs) Re: Murchison...10 Billion years?

Someone wrote (kindly forwarded by George Z.):

>The age of the grains is determined by the fact
>that a star with 1.2 times the mass of the Sun, "lives" for about 6 billion
>years. This indicates the grains were formed at the end of a star's cycle.
>Now, to get the age of the Milky Way, take into account the 4.6 billion
>year history of our Solar system, and add it to the fact that the grains
>formed in the death of a star with a 6 billion year life. You will come up
>with a value of 10.6 billion years.

You say the grains were formed in the death of a star with a 6 billion
year life. If that's the case, you can't simply add 4.6 and 6 to get
10.6!(?) Heavy elements like C and Si are formed towards the end of
a star's life, not the beginning.

If we assume that our solar system began to form 5 billion years ago
(I believe the Earth was "finished" 4.6 b.yr. ago) then a likely age
of the grains will rather be something like 5 b.yr. + some million years.

Or have I lost something here? Are the grains assumed to have been made
in yet an earlier generation of star? Something like:
--> Big star --> make grains --> go BOOM -->
1.2 Sunmass star --> big red thing --> planetary nebula -->
pre-Solar nebula --> Sun++ ???

All the best,
Trond