(a) Use Fig. 29.21 to explain why there is essentially no naturally occurring 239Pu in or on the Earth at present.

(b) Use the information in the figure to explain why there is very little (but not zero) 235U naturally occurring in or on the Earth.
(c) For every 1000 kg of 239P that might have been present at the time the Earth was formed, how much is currently left? Does this corroborate the qualitative reasoning in part (a)?
(d) Estimate how much 235U would be left from each 1000 kg of 239P. Because the 239P half-life is so short compared to that of 235U, you can assume that the full 1000 kg of 239P decayed into 235U while no significant decay of that nucleus occurred. Does this corroborate the qualitative reasoning in part (b)?

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146 145 144 143 142 141 140 139 138 137 136 E 135 134 3,2 10 189 21 mn 11.2 d 5 133 3.92 s Z 132 131-H 830us 130 128216 min 127 126 125 124 sta 80 81 82 83 84 85 56 87 88 89 90 91 92 9 94 Proton number (Z)