SciencePrecambrian (~1.6 billion years ago)Australiahigh confidence

Chemical evidence from Australia's Barney Creek Formation indicates that eukaryotes—organisms with clearly defined cell nuclei—existed at least 1.6 billion years ago.

Notes on verification

Confirmed by peer-reviewed study (published in PNAS, indexed on PubMed) and corroborated by multiple reputable science news outlets (CNN, Science News, Phys.org, NHM, GFZ). [cascade flags: aggregator_dropped_primary_exists | tier=silver indep_score=0.87 clusters=5 claim_tier=notable]

Sources