A Greenland ice-core study by Michail Petaev, Shichun Huang, Stein Jacobsen, and Alan Zindler found almost no iridium but detected a pronounced platinum spike beginning exactly 12,900 years ago.
Notes on verification
Confirmed by the original 2013 PNAS paper (Petaev et al.) and corroborated by independent secondary sources. Minor nuance: a later review notes a very weak extended iridium signal was detected, consistent with 'almost no iridium' rather than absolute zero. [cascade flags: aggregator_dropped_primary_exists | tier=silver indep_score=1.0 clusters=3 claim_tier=exceptional]
Sources
- Did a Comet Really Kill the Mammoths 12,900 Years Ago? (seed:history_and_archaeology)
- https://www.pnas.org/doi/10.1073/pnas.1303924110 (corroboration)
- https://pubmed.ncbi.nlm.nih.gov/23878232/ (corroboration)
- https://www.nature.com/articles/srep44031 (corroboration)