What was the primordial composition of U isotopes in solar system? Solar system contained isotopes less than a million year halflife, because meteors have clear traces of having crystallized with abundant aluminium 26. So, what was the actinide composition? We know the exact amount of uranium 238 because her longest lived mother is Pu-242, half-life 373 000 years. All uranium 238 was in Solar System primordially - she has only decayed since, at a predictable rate and known final amount. Not so with uranium 235. For though the halflife of U-235 and remaining amount is known, U-235 unlike U-238 has a long lived mother - Cm-247 with half-life of 15,6 million years. Since Cm-247 is now completely extinct, is it known what fraction of U-235 was primordial and what fraction is daughter of Cm-247? Now, concerning uranium... Uranium 236 is also an isotope of uranium. She is herself long lived - 23,5 million years half-life - and daughter of even longer lived - 80 million years - plutonium 244. Considering uranium 236 and plutonium 244 are both long lived, did primordial solar system contain excess uranium 236 (primordial amounts) or was the solar system short of uranium 236 till she formed by decay of plutonium 244? Finally, neptunium 237 has a half-life 2,2 million years. Her daughters include uranium 233. Therefore, the primordial U composition would have been: U-238 (all there, known amount) U-234 (already in equilibrium as daughter of U-238, so known amount) U-235 (how much had formed?) U-236 (how much was there?) U-233 (same question) Can anyone provide the numbers for that isotopic composition?