Making Chicxulub

Everyone agrees Chicxulub wasn't from here. Since February 2021 a consensus has formed is that it was a carbonaceous chondrite. These are rare down here but they do get here; 142 Polana, for instance, is in the B class of these and has spawned many a pile of dangerous rubble. But I don't think many believe that Polana dropped the bomb on me (baby).

Instead, Makhatadze's team say: the Ornans class, CO or maybe CT. They did this by measuring the nickel isotopes. A CO / CT might be, or have been, carboniferous but the harder stuff is in there, even prevalent now (see below).

As hinted, carbonaceous chondrites are diverse. Which one was it? Hence the check for nickel. This comes in five isotopes as might have halflives beyond the 4.567Gy after coalescing into CCs. Each type of CC formed in different environments with their own recipes for nickel. They say CI is special here, and that CY (which is new) groups with them. Which led them to exonerate this whole subgroup from our crater.

Previous estimates had clustered around CM. The nickel rules closer to CO. They formed around the same place, 3.7 AU; they are differentiated, as it were, in time, CO forming earlier. CT is also possible but they aren't as well-constrained as yet, and as North Americans say when they hear hoofbeats, horses be more likely than zebras.

CO Chondrites are also, they say, dry - until this one splashed into shallow water that is. Previous estimates on the sulfur sent into the atmosphere had been estimated from the assumption of a sulfur-rich CM so those estimates are going to have to change. Unless the monster struck an oil field admittedly, and this is the future Gulf of America we are discussing here.

They point to Bottke 2007 as one line of evidence, on this rock coming from a 160Mya breakup. That would be the 298 Baptistina hypothesis. I know Bottke's been around awhile but I personally would not do this, except as a nod to those discredited pre-CC theories. Because it's the wrong rock (it's S) at the wrong time (80 Mya). CO rocks instead formed past the present (and CM era?) snowline although perhaps not the 2.7My-after-solar-system snowline. We are here not discussing the Grand Tack.

I have to wonder about 495 Eulalia ...