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Re: iridium

James R. Cunningham wrote:

> > At 08:28 PM 5/6/98 -0700, Earl Wood wrote:
> > >     I would like to know if anyone has calculated the amount of Iridium
> > >needed to
> > >cover the entire earths surface , at the depth associated with the K C
> > >boundary ? and if so does anyone have these figures , or a reference
> > >that would be available to Joe citizen ?
> This is from memory, so is untrustworthy.  I believe I read some years
> ago that assuming iridium concentrations typical of other meteors, it
> would have taken an asteroid about 5-8 miles in diameter to contain the
> iridium needed to match measured amounts at the K-T boundary.
>                         Best wishes,
>                                 Jim

     In my efforts to find the answer to this question , I looked at the
Alvarez work on this question and their figures state.......common meteorites
have iridium of about 500 parts per billion, they calculated that the world
wide iridium anomaly at about ( 0.5 million tons)to introduce that much iridium
would require a meteorite 10 kilometers in diameter ,
slightly larger than the nucleus of Halley's comet . This was taken from their
paper in
Science magazine.  Just a refresher in case you are interested. Thanks for your
I really appreciate any help I can Get..
     Earl Wood