Moved
The galaxy runs on explosions
The isotope record is the part of this that bears on the argument, and it is now stated beside the argument it bears on.
Where it went
The isotopes, and the two dates.
Iron-60 cannot be made here and cannot have been here since the planet formed, because half of any amount decays away every two and a half million years. It has been found in Pacific, Atlantic and Indian Ocean seabed, in lunar samples, and as of 2026 in Antarctic ice.
Nearby supernovae dusted the Earth at least twice inside the last ten million years and nothing was sterilised, which is the step the old isotope argument needed and does not have. Heliospheric modelling puts cloud crossings at about the same two dates from a completely separate method. Both halves are argued on the claim.