Again, how often does Science magazine have an article that’s not biochem, molecular bio, or field bio? Well, in vol. 385 # 6710, for 15 Aug, here’s one:
Fischer-Gödde, M. Tusch, J. Goderis, S. et al. Ruthenium isotopes show the Chicxulub impactor was a carbonaceous… p. 752 10.1126/science.adk4868
We know elemental assays (including isotope measurements) for Earth, meteorites, Earth’s satellite, etc. to many decimal places. This now includes Vesta (through our HED meteorites), Ryugu, Bennu (final data TBC), Mars (through our Martian meteorites …for now), the solar wind/photosphere (via Genesis) and to an extent a comet (Wild 2, via the samples from Stardust). It will soon include Phobos (which will likely have minor bits of Mars), and other sample return missions to non-earth bodies are in formulation (Kamo’oalewa, we’re working our way to you).
Using these element/isotope inventories, it’s a straightforward matter to extend forward/backward (via the history of the Solar System, and limited mixing of pools) and left/right (to similar bodies, of a given population of bodies). One such fore/back is impact sites, ‘contaminated’ with meteor material. And since the impact that wiped out the dinosaurs was one serious impact, we’ve got the contaminants. All around the impact site (the Chicxulub structure, in Mexico), we find a layer of impactor materials that don’t quite match Earth material- hence, an impact. They do, however, match (depending on your comparison) the chemical inventories of extraterrestrial bodies.
Fischer-Gödde et al. do the inventory. According to their paper, we’re one step closer to the ‘mugshot’ of this dino-killer. Based on rubidium isotopes (a good tracer), we can profile the layer deposited around Mexico and the surrounding Gulf, and it matches carbonaceous-chondrite asteroids. And carbonaceous chondrite bodies, as we’ve seen previously, came from the outer Solar System. The debate between ‘was it a comet’ and ‘was it an asteroid’ is, assuming they’re onto something here, not much of a debate at all. Carbonaceous asteroids are, one or two steps at least, from a similar origin to comets in the early, outer, cold Solar System. And the Chicxulub disaster was one more example of deposition via carbonaceous strikes to the Earth- this one happened to be later than the others.