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22
220 ppm relative to silicon equal to I8.5 percent by weight in
primitive nonvolatile solar material. Ihis is one fourth of its
reported abundance. We use this somewhat larger factor because
Urey's (1955) calculations indicate that his choice of radioactive
elements is somewhat too high for reasons which he
discusses. Also, the somewhat lower abundance gives a somewhat
smoother abundance curve. This gives 854 for its atomic abundance.
The use of this abundance leads to the similarity in shape of the
even and odd mass curves in the minimum region between oxygen
and iron.
As explained above, the choice of this lov;er value for
potassium requires that other abundances by adjusted if we are to
be consistent. It seems likely that the melting processes which
produced the silicate minerals produced the fractionation of
potassium, uranium and thorium, and in this case the abundances of
all elements which are markedly concentrated by such processes
must be appropriately adjusted as well. In order to Judge the
direction and amount of such adjustments we have studied the
relative abundances of the elements in the earth*s crust and in
the meteorites. Potassium makes up 2.6 percent of the earth's
surface rocks and only O.O9 percent of the meteorites. Also,
analyses of ultramafic rocks show that potassium is very low in
these rocks. Ross, Poster and Myers (1954) analysed olivine bombs
from basaltic lava flows and found low values for sodium and
potassium and Edwards (1955h) using an improved method of analysis