age of the earth

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

One of our subscribers is having some difficulty, so I'm posting this
on her behalf:

"Bonnie Blackwell, Dept of Geology, (718) 997-3332"
<bonn@qcvaxa.acc.qc.edu> says (in relation to previous conversations
about whether or not the earth is 4550 MY old):

> the age of the earth is assumed from the age of the meteorites found
> on earth and the oldest moon rocks.  the age of the accretion of the
> planet is assumed to begin at about the same time as the white
> nodules get locked into the canyon diablo meteorite.  those nodules
> contain odd 16O/17O ratios suggesting that they come from a nearby
> supernova in the galaxy that started the solar system's
> condensation.  from 129Xe and other isotopes found in the
> meteorites, they can figure fairly precisely how long the solar
> nebula takes to collapse and condense.  these isotopes all have
> fairly short half lives and occur in some meteorites but not on
> earth, etc.  for a good relatively elementary discussion of this
> see, Faure, Principles of Inorganic Geochemistry; Stacy, Physics of
> the Earth (an oldy but goody); or any good geochemistry or
> geophysics text.  hope this helps...  
> b