SciencePleistocene-Holocene (~16,800-11,000 years ago)global (notably California Channel Islands)high confidence

Carbon spherules were found in soil layers dating from before, during, and after the Younger Dryas event, not just at its onset.

Notes on verification

Confirmed by independent peer-reviewed studies (Scott et al. 2010 in GRL, with AGU press release, and a 2011 review) showing carbon spherules occur across a wide time range, not just at the Younger Dryas onset. This directly counters the impact hypothesis proponents' claims, making it a contested but well-corroborated scientific finding. [tier=gold indep_score=0.983 clusters=3 claim_tier=notable]

Sources