View Document - OSTI

46
ppm are not presented with great confidence by him, but they
appear to be approximately correct. The ratio of these values
is perhaps 25 as an average. The ratio of potassium in the
earth's crust, i.e, 2,6j6, to its amount in the chondrites, 0.09Ji,
is about 29. Also, uranium and thorium are concentrated in the
earth's surface relative to the chondrites by the same factor
roughly. The evidence indicates that lead is concentrated along
with potassium, uranium and thorium in melting processes, and is
apparently lithophile in character and not chalcophile BO far
as these processes arc concerned. Rankama and Sahama (1950, P, 97
ff) discuss this character of lead.
Xn view of the above argtmient we calculate the lead
abundances as follows. We take Urey^s (1955) estimate for the
uranium abundance in solar matter at the present time as 0.0332
ppm of the nonvolatile fraction, which is 1/3,19 of chackett's et al
(195O)
value for uranium in the Beddegelert meteorite. It is nearly all
u238. Since the half life of u258ig 4,51 x lo9 years, the amount
of U^^^