Harvard researchers calculated that distributing approximately 30 parts per trillion of platinum worldwide would have required a meteorite about half a mile across, large enough to leave a substantial crater.
Notes on verification
Confirmed by the original 2013 PNAS study (Petaev et al.) and corroborated by National Geographic and Phys.org reporting, which accurately reflect the researchers' calculations about platinum distribution and meteorite size.
Sources
- Did a Comet Really Kill the Mammoths 12,900 Years Ago? (nationalgeographic.com)
- https://www.pnas.org/doi/10.1073/pnas.1303924110 (pnas.org)
- https://martinsweatman.blogspot.com/2021/05/the-following-article-has-been-accepted.html (martinsweatman.blogspot.com)