https://world-nuclear.org/information-library/nuclear-fuel-c...
We can calculate the abundances of U-235 and U-238 at the time the Earth was formed. Knowing further that the production ratio of U-235 to U-238 in a supernova is about 1.65, we can calculate that if all of the uranium now in the solar system were made in a single supernova, this event must have occurred some 6.5 billion years ago.
This 'single stage' is, however, an oversimplification...
The really interesting thing is that phrase "the production ratio of U-235 to U-238 in a supernova is about 1.65"; the now-rare U-235 is actually more abundant than U-238 in the fresh debris of a supernova. Prolonged aging has preserved more U-238 (half life 4.47 billion years) than U-235 (half life 0.704 billion years) to the point that U-238 is now much more terrestrially abundant. If Earth had been formed with uranium that rich in U-235, there would have been Oklo events all over the place. Uranium wouldn't need isotopic enrichment to be used as fuel in light water reactors. Nuclear fission would probably have been discovered early in the 19th century, soon after the element itself was recognized, because any substantial quantity dissolved in aqueous solution would have reached criticality.
If the Uranium came from multiple supernovae, then why is it shocking that earth has different concentrations of U235? Moreover, how is it proof of a past fission reaction?
What if that "part" of U235 came from a separate supernova which is a little older and some more of its U235 had already decayed?
> Your taste develops faster than your skill
> "the quality group could tell you why a photograph was excellent"
They are critics now. People with a huge taste-skill gap are basically critics — first towards themselves and gradually towards others. I don't want to generalize by saying "critics are just failed creators", but I've certainly found it true for myself. Trying to undo this change in me and this article kind of said all the words I wanted to hear. :)
It's both dense and beautifully written. Feels like every paragraph has something profound to say. This kind of "optimizing-for-screenshot-shares" writing usually gets overdone, but since this actually had substance, it was amazing to read.
(See how I turned into a critic?)