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A comet impact or airbursts triggered the Younger Dryas about 12,800 years ago

Status: Contested Verdict: Open question; several key papers retracted 2025–26

The claim: Earth passed through the debris of a fragmenting comet about 12,800 years ago. Airbursts and impacts caused widespread fires, an 'impact winter', megafaunal extinctions and the Younger Dryas cooling.

Why this label: Proposed in PNAS in 2007 and supported by dozens of papers reporting platinum spikes, microspherules, nanodiamonds and soot at the onset layer. A large 2023 review argues the evidence is not unique to impacts and is poorly dated. In 2025–26 three high-profile supporting papers were retracted (authors disagreed). The published record has evidence on both sides, so the hypothesis is Contested.

Background

This is the scientific core of the '12,000-year catastrophe' idea. Supporters, many in the Comet Research Group, point to a platinum anomaly in Greenland ice lasting about 21 years, a biomass-burning signal in several ice cores, and melt-glass at sites such as Abu Hureyra in Syria. Critics note that no crater of the right age has been found and that the proxies also form by ordinary processes. Greenland's Hiawatha crater, once floated as a candidate, was dated in 2022 to about 58 million years. Weighting the newest observations cuts both ways here: new supporting data keep appearing, and so do retractions of supporting papers.

What has been measured

Dates, measurements and documented findings, kept separate from interpretation.

Evidence and arguments for

  • Original multi-proxy case from sites across North America and Europe. [1]
  • Biomass-burning and platinum anomalies in ice cores at the Younger Dryas onset. [2]
  • High-temperature melt-glass at Abu Hureyra, Syria, at the onset layer. [3]
  • A matching proxy layer reported in Patagonia, Chile, suggesting a hemispheric event. [4]
  • A 2021 review assembles the impact evidence and argues it is consistent across sites. [5]

Evidence and arguments against, or limits

  • The 2023 review argues the proxies are not unique to impacts, are often poorly dated, and that no crater of the right age exists. [6]
  • Recent retractions cite problems with age models, sampling and particle identification in supporting studies. [10][11][9]

Open questions & what would change the label

Blind, multi-lab analysis of the same samples across the onset layer and sections above and below it; high-resolution dating showing the proxies are synchronous within decades; and a confirmed impact structure or a unique impact signature such as shocked minerals with diagnostic features.

Sites

Göbekli Tepe

Related claims

Sources

  1. Firestone, R. B. et al. (2007). Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. PNAS 104. doi:10.1073/pnas.0706977104 proponent
  2. Wolbach, W. S. et al. (2018). Extraordinary biomass-burning episode and impact winter triggered by the Younger Dryas cosmic impact ~12,800 years ago. 1. Ice cores and glaciers. Journal of Geology 126. doi:10.1086/695703 proponent
  3. Moore, A. M. T. et al. (2020). Evidence of cosmic impact at Abu Hureyra, Syria at the Younger Dryas onset (~12.8 ka). Scientific Reports 10 (later corrected). doi:10.1038/s41598-020-60867-w proponent
  4. Pino, M. et al. (2019). Sedimentary record from Patagonia, southern Chile supports cosmic-impact triggering of biomass burning, climate change, and megafaunal extinctions at 12.8 ka. Scientific Reports 9. doi:10.1038/s41598-018-38089-y proponent
  5. Sweatman, M. B. (2021). The Younger Dryas impact hypothesis: review of the impact evidence. Earth-Science Reviews 218. doi:10.1016/j.earscirev.2021.103677 proponent
  6. Holliday, V. T. et al. (2023). Comprehensive refutation of the Younger Dryas Impact Hypothesis (YDIH). Earth-Science Reviews 247. doi:10.1016/j.earscirev.2023.104502 critique
  7. Kjær, K. H. et al. (2018). A large impact crater beneath Hiawatha Glacier in northwest Greenland. Science Advances 4. doi:10.1126/sciadv.aar8173 data
  8. Kenny, G. G. et al. (2022). A Late Paleocene age for Greenland's Hiawatha impact structure. Science Advances 8. doi:10.1126/sciadv.abm2434 data
  9. Scientific Reports (24 Apr 2025). Retraction note: 'A Tunguska sized airburst destroyed Tall el-Hammam...' (Bunch et al. 2021); several authors disagree. doi:10.1038/s41598-025-99265-5 notice
  10. PLOS ONE editors (11 Feb 2026). Retraction: 'Shocked quartz at the Younger Dryas onset (12.8 ka) supports cosmic airbursts/impacts...' (Kennett et al. 2025): age-model and sampling concerns; eight authors disagree. doi:10.1371/journal.pone.0342620 notice
  11. PLOS ONE editors (11 Feb 2026). Retraction: 'A 12,800-year-old layer with cometary dust, microspherules, and platinum anomaly ... Baffin Bay' (Moore et al. 2025): calibration and particle-identification concerns; several authors disagree. doi:10.1371/journal.pone.0342613 notice

More in this section: Younger Dryas & the 12,000-year cycle.

Sources checked against Crossref and publisher pages on 2026-10-22. Labels describe the claim, not the people who hold it. Methodology.