[ RadSafe ] 4.4 billion year old crystal

[JPreisig at aol.com]

Hmmmm,
 
      See the geophysics book by Stacey.  or  Brownlow's Geochemistry.
 
 
      Joe Preisig
 
 
 
In a message dated 2/24/2014 5:58:41 P.M. Eastern Standard Time,  
Jeffrey.Kulp at DOH.WA.GOV writes:

Hello  Radsafers,



I have a question about a news story I just read; it  said that
scientists in Australia had discovered a 4.4 billion year old  zircon
crystal. 



The article went on to say that they had  dated it using uranium decay to
lead. 



My question is how do  they know what concentration of uranium the
crystal started with? At  present the concentration of uranium in the
earth's         crust varies
quite a bit (two orders of magnitude or more?). Was the U  concentration
more uniform back when the crust just  formed?



Given that the half-life of U-238 is roughly 4.4  billion years, how can
they be so sure of its age?



Thanks in  advance for the information




Jeffrey Kulp,  RRPT

Radiation Health Physicist

Washington State Department of  Health - ORP

16201 E. Indiana Ave. Suite 1500

Spokane Valley, WA  99216

(509) 329-2138 (Office)

(509) 329-2154  (Fax)

"Public Health - Always Working for a Safer and Healthier  Washington"





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