UC Davis reports on Kr-78 (radioactive, but a slow burn) and -80 in our "deep mantle". Kr-86 too where they could get it. Kr-84 is most common here at 57%.
Deep mantle is Earth before 44254460 Mya. It sends its hot rocks to research-accessible depths at Iceland, cross-checked with Galapagos. This magma looks like carbonaceous(?) chondrites: although, less Kr-86 than the 17.28% we find up there. Our mantle in turn differs from this its crust. Tho' carbon tends to signify outer belt...
UPDATE 12/23: ... ah. They're non-carbonaceous. Like chondrites that would have formed in the inner system, but no longer exist free of inner planets.
So they think that the Kr-86 in our crust and air would have been delivered by, exactly, meteorites; after the Big Splat.
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