What caused the end-Cretaceous mass extinction of the non-avian dinosaurs: the Chicxulub asteroid impact, Deccan Traps volcanism, or both?
About 66 million years ago roughly three-quarters of Earth's species, including all non-avian dinosaurs, died out at the Cretaceous-Paleogene boundary. Two very large events sit at that boundary: a giant asteroid impact at Chicxulub in Mexico and a prolonged episode of flood-basalt volcanism in India called the Deccan Traps. This ledger tracks the primary peer-reviewed evidence for what is established, what is disputed, and what remains open.
9 established, 1 disputed, 1 debunked, 1 unresolved. We do not pick an answer; the evidence places each claim. How we decide
29 citations from 11 independent sources - 18 echo the same voices and count once. Graded A1-D1.
Added 3 Jul 2026 - updated 29 Sept 2026
What the four states mean
- Establishedsupported, uncontested
- Disputedcredible sources disagree
- Debunkedrefuted by the evidence
- Unresolvedno settled answer
Established 9supported, uncontested
The relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms have been the subject of intense debate.▰▰▰▱▱ likely2 points
Supports- Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event.Chiarenza et al. 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction (PNAS 117) authoritative
- The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary.Hull et al. 2020, On impact and volcanism across the Cretaceous-Paleogene boundary (Science 367) authoritative
Deep-sea limestones in Italy, Denmark and New Zealand show iridium increases at the time of the Cretaceous-Tertiary extinctions. Because platinum metals are depleted in Earth's crust, the iridium was argued to be extraterrestrial, and the impact of a large earth-crossing asteroid was proposed to account for the extinctions.▰▰▱▱▱ likely3 points
Supports- Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material.Alvarez, Alvarez, Asaro & Michel 1980, Extraterrestrial Cause for the Cretaceous-Tertiary Extinction (Science 208) authoritative
- Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago.Alvarez, Alvarez, Asaro & Michel 1980, Extraterrestrial Cause for the Cretaceous-Tertiary Extinction (Science 208) authoritative
- Reasons are given to indicate that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is suggested which accounts for the extinctions and the iridium observations. Impact of a large earth-crossing asteroid would inject about 60 times the object's mass into the atmosphere as pulverized rockAlvarez, Alvarez, Asaro & Michel 1980, Extraterrestrial Cause for the Cretaceous-Tertiary Extinction (Science 208) authoritative
Four independent estimates of the asteroid's diameter in the original impact hypothesis gave values in the range of 10 plus or minus 4 kilometers.▰▰▱▱▱ likely1 source
Supports- Four different independent estimates of the diameter of the asteroid give values that lie in the range 10 +/- 4 kilometers.Alvarez, Alvarez, Asaro & Michel 1980, Extraterrestrial Cause for the Cretaceous-Tertiary Extinction (Science 208) authoritative
A buried 180-km-diameter circular structure on Mexico's Yucatan Peninsula was proposed as an impact crater. Its andesitic rocks have chemical and isotopic compositions similar to tektites found in Cretaceous/Tertiary ejecta, and a K/T boundary age is indicated.▰▰▱▱▱ likely3 points
Supports- We suggest that a buried 180-km-diameter circular structure on the Yucatán Peninsula, Mexico, is an impact crater.Hildebrand et al. 1991, Chicxulub Crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico (Geology 19) authoritative
- The andesitic rocks have chemical and isotopic compositions similar to those of tektites found in Cretaceous/Tertiary (K/T) ejecta.Hildebrand et al. 1991, Chicxulub Crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico (Geology 19) authoritative
- The age of the crater is not precisely known, but a K/T boundary age is indicated.Hildebrand et al. 1991, Chicxulub Crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico (Geology 19) authoritative
High-precision argon dating indicates that more than 90% of the Deccan Traps volume erupted in less than 1 million years, with about 75% emplaced after the Cretaceous-Paleogene boundary.▰▰▱▱▱ likely2 points
Supports- We constrain the location of the KPB with high-precision argon-40/argon-39 data to be coincident with changes in the magmatic plumbing system.Sprain et al. 2019, The eruptive tempo of Deccan volcanism in relation to the Cretaceous-Paleogene boundary (Science 363) authoritative
- We also found that the DT did not erupt in three discrete large pulses and that >90% of DT volume erupted in <1 million years, with ~75% emplaced post-KPB.Sprain et al. 2019, The eruptive tempo of Deccan volcanism in relation to the Cretaceous-Paleogene boundary (Science 363) authoritative
A synthesis of the global stratigraphy across the boundary concluded that the Chicxulub impact triggered the mass extinction.▰▰▱▱▱ likely2 points
Supports- Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary.Schulte et al. 2010, The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary (Science 327, 41-author review) analysis
- The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.Schulte et al. 2010, The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary (Science 327, 41-author review) analysis
Carbon cycle modeling with paleotemperature records found major volcanogenic outgassing beginning and ending distinctly before the impact, with only the impact coinciding with the mass extinction.▰▰▱▱▱ likely2 points
Supports- We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing.Hull et al. 2020, On impact and volcanism across the Cretaceous-Paleogene boundary (Science 367) authoritative
- We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change.Hull et al. 2020, On impact and volcanism across the Cretaceous-Paleogene boundary (Science 367) authoritative
In climate and habitat models, an asteroid impact winter suppresses potential global dinosaur habitats, while long-term Deccan volcanism leads to increased habitat suitability.▰▰▱▱▱ likely2 points
Supports- Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats.Chiarenza et al. 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction (PNAS 117) authoritative
- Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO2]-induced warming) leads to increased habitat suitability.Chiarenza et al. 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction (PNAS 117) authoritative
Global plant fossil and pollen data show that the Chicxulub impact triggered widespread destruction of forests.▰▰▱▱▱ likely1 source
Supports- Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9].Field et al. 2018, Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction (Current Biology 28) authoritative
Disputed 1credible sources disagree
Deccan Traps volcanism contributed to the end-Cretaceous ecosystem crisis.▰▰▰▱▱ likely1 against3 points
Supports- Late Cretaceous records of environmental change suggest that Deccan Traps (DT) volcanism contributed to the Cretaceous-Paleogene boundary (KPB) ecosystem crisis.Sprain et al. 2019, The eruptive tempo of Deccan volcanism in relation to the Cretaceous-Paleogene boundary (Science 363) authoritative
- Our results closely match observed and proxy data and suggest decoupled CO 2 and SO 2 emissions, a two-step decline in export productivity with a protracted recovery, and no clear volatile impulse at the boundary.Cox & Keller 2023, A Bayesian inversion for emissions and export productivity across the end-Cretaceous boundary (Science 381) authoritative
Against- These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.Chiarenza et al. 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction (PNAS 117) authoritative
Debunked 1refuted by the evidence
The end-Cretaceous extinction killed every dinosaur.Refuted by
In fact, some dinosaurs survived the asteroid apocalypse.
refuted3 against4 pointsThe claim rested on- It is the myth that dinosaurs are gone, felled one and all during the end-Cretaceous extinction.How birds survived the dinosaurs' doomsday (Steve Brusatte, Scientific American) summary
Refuted by- In fact, some dinosaurs survived the asteroid apocalypse.How birds survived the dinosaurs' doomsday (Steve Brusatte, Scientific American) summary
- Although canonical species such as T. rex and Triceratops perished, members of one dinosaur group managed to endure: birds.How birds survived the dinosaurs' doomsday (Steve Brusatte, Scientific American) summary
- The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1-3].Field et al. 2018, Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction (Current Biology 28) authoritative
Unresolved 1no settled answer
Whether dinosaurs were in long-term decline before the end-Cretaceous extinction, or thriving until it, has not been settled.▰▰▰▱▱ likely1 against4 points
Supports- Whether dinosaurs were in a long-term decline or whether they were reigning strong right up to their final disappearance at the Cretaceous-Paleogene (K-Pg) mass extinction event 66 Mya has been debated for decades with no clear resolution.Sakamoto, Benton & Venditti 2016, Dinosaurs in decline tens of millions of years before their final extinction (PNAS 113) authoritative
- In the lead-up to the Cretaceous/Paleogene mass extinction, dinosaur diversity is argued to have been either in long-term decline, or thriving until their sudden demise.Chiarenza et al. 2019, Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction (Nature Communications 10) authoritative
- We find overwhelming support for a long-term decline across all dinosaurs and within all three dinosaurian subclades (Ornithischia, Sauropodomorpha, and Theropoda)Sakamoto, Benton & Venditti 2016, Dinosaurs in decline tens of millions of years before their final extinction (PNAS 113) authoritative
Against- We suggest that Maastrichtian North American dinosaur diversity is therefore likely to be underestimated, with the apparent decline a product of sampling bias, and not due to a climatically-driven decrease in habitability as previously hypothesised.Chiarenza et al. 2019, Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction (Nature Communications 10) authoritative
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