Asteroid impact and volcanic activity that caused the extinction of non-avian dinosaurs
End of an epoch
For more than 150 million years, dinosaurs dominated terrestrial ecosystems, while marine reptiles like mosasaurs, plesiosaurs, and flying reptiles – pterosaurs – thrived in the seas and skies. This long Mesozoic success abruptly ended 66 million years ago, at the Cretaceous–Paleogene (K–Pg) boundary (formerly called “K–T”). Within a relatively short geological interval, non-avian dinosaurs, large marine reptiles, ammonites, and many other species went extinct. The surviving groups – birds (avian dinosaurs), mammals, some reptiles, and selected parts of marine fauna – inherited a drastically changed world.
At the center of this K–Pg extinction is the Chicxulub impact – a catastrophic collision of an asteroid or comet about 10–15 km in diameter in the region of the present-day Yucatán Peninsula. Geological evidence strongly confirms this cosmic event as the primary cause, although volcanic eruptions (the so-called Deccan Traps in India) added additional pressure due to greenhouse gases and climate change. This combination of forces brought an end to many Mesozoic lineages, marking the fifth major mass extinction. Understanding this event allows us to see how sudden, widespread shocks can disrupt even seemingly invincible ecological dominance.
2. The world of Credo before the impact
2.1 Climate and biota
During the Late Cretaceous (~100–66 million years ago), the Earth was relatively warm, with high sea levels flooding the interiors of continents, forming shallow epicontinental seas. Angiosperms (flowering plants) flourished, creating diverse terrestrial habitats. Dinosaur faunas included:
- Theropods: Tyrannosaurs, dromaeosaurs, abelisaurs.
- Ornithischians: Hadrosaurs (“duck-billed”), ceratopsians (Triceratops), ankylosaurs, pachycephalosaurs.
- Sauropods: Titanosaurs, especially in southern continents.
In the seas, mosasaurs dominated as apex predators, along with plesiosaurs, and ammonites (cephalopods) were abundant. Birds had already diversified, mammals occupied relatively small niches. Ecosystems appeared stable and vibrant until the K–Pg boundary.
2.2 Deccan Traps volcanism and other stressors
In the Late Cretaceous, massive Deccan Traps eruptions began on the Indian subcontinent. These basaltic flows released CO2, sulfur dioxide, aerosols, possibly warming or acidifying the environment. Although this alone was probably insufficient to cause extinction, it could have weakened ecosystems or caused gradual climate effects, preparing for something even more drastic [1], [2].
3. Chicxulub impact: evidence and mechanism
3.1 Discovery of the iridium anomaly
In 1980, Luis Alvarez and co-authors discovered a layer rich in iridium at the K–Pg boundary in Gubbio (Italy) and other sites. Since iridium is scarce in the Earth's crust but more abundant in meteorites, they proposed that a large impact was the cause of this extinction. This layer was also characterized by other impact indicators:
- Shock quartz (English: shocked quartz).
- Microtektites (small glass spherules formed during rock vaporization).
- High concentration of platinum group elements (e.g., osmium, iridium).
3.2 Crater location: Chicxulub, Yucatán
Later geophysical studies discovered a crater about 180 km in diameter (Chicxulub crater) beneath the Yucatán Peninsula in Mexico. It precisely matches an asteroid/comet impact of about 10–15 km in diameter: there are signs of shock metamorphism, gravitational anomalies, and drill cores reveal disturbed rock layers. Radiometric dating of these rocks coincides with the K–Pg boundary (~66 million years ago), thus finally proving the link between the crater and the extinction [3], [4].
3.3 Impact dynamics
During the impact, kinetic energy equivalent to billions of atomic bombs was released:
- Shock wave and ejecta: Rock vapors and molten debris rose to the upper atmospheric layers, possibly falling out globally.
- Fires and heat wave: Global fires could have been ignited again by returning ejecta fragments or overheated air.
- Abundance of dust and aerosols: Fine particles blocked sunlight, drastically reducing photosynthesis during several months or years of "impact winter."
- Acid rain: Sulfur and CO2 were released by evaporation of anhydrite or carbonate rocks, causing acid precipitation effects and climate perturbations.
This combination of short-term darkness/cold and long-term greenhouse effects caused widespread damage to terrestrial and marine ecosystems.
4. Biological impact and selective extinctions
4.1 Terrestrial losses: non-avian dinosaurs and others
Non-avian dinosaurs, from top predators like Tyrannosaurus rex to huge herbivores like Triceratops, went completely extinct. Pterosaurs also died out. Many smaller terrestrial animals dependent on large plants or stable ecosystems suffered heavy losses. Yet certain lineages survived:
- Birds (avian dinosaurs) – possibly survived due to smaller size, seed-based diet, and more flexible feeding.
- Mammals: Also affected, but recovered faster and quickly evolved into larger forms in the Paleogene.
- Crocodiles, turtles, amphibians: Aquatic/semi-aquatic groups also managed to survive.
4.2 Marine extinctions
In the oceans, mosasaurs and plesiosaurs went extinct, along with many invertebrates:
- Ammonites (long-lived cephalopods) went extinct, though nautiloids survived.
- Planktonic foraminifera and other microfossil groups suffered heavily, important in marine food webs.
- Corals and bivalves experienced partial or local extinctions, but certain genera recovered.
During the "impact winter," the decline in primary production likely starved marine food webs. Species less dependent on steady production or able to feed on detritus survived better.
4.3 Survival patterns
Smaller, more generalist species, able to feed flexibly or adapt, survived more often, while large or highly specialized creatures went extinct. This size/ecological specialization "selectivity" may indicate that a combination of severe environmental changes (darkness, fires, greenhouse) disrupted the entire established chain.
5. The role of Deccan Traps volcanism
5.1 Timing coincidence
Deccan Traps eruptions in India left extensive basalt layers dated to the K–Pg boundary, releasing massive amounts of CO2 and sulfur. Some scientists believe this alone could have caused major environmental crises, possibly in the form of warming or acidification. Others think this volcanism was a major stressor, but the main "fatal blow" was dealt by the Chicxulub cosmic body.
"5.2 The hypothesis of combined effects"
"It is often stated that Earth was already \"stressed\" due to the Deccan eruptions – with possible warming or partial ecosystem disruptions – when the Chicxulub impact finally destroyed everything. This interaction model explains why the extinction was so total: multiple factors together overwhelmed ecosystem resilience." [5], [6].
"6. Consequences: A new age of mammals and birds"
"6.1 The Paleogene world"
"Groups surviving past the K–Pg boundary rapidly spread during the Paleocene epoch (~66–56 million years ago):"
- "Mammals expanded into free niches previously occupied by dinosaurs, transitioning from small, possibly nocturnal forms to various sizes."
- "Birds branched out, occupying niches from flightless land birds to water-specialized forms."
- "Reptiles – crocodiles, turtles, amphibians, and lizards – survived or diversified in new free habitats."
"Thus, the K–Pg event acted like an evolutionary \"reboot\", similar to other mass extinction cases. The foundations of today's terrestrial biotas developed through newly constructed ecosystems."
"6.2 Long-term climate and diversity trends"
"During the Paleogene, Earth's climate gradually cooled (after the short Paleocene–Eocene thermal maximum), which led to further mammal expansion, eventually giving rise to primates, ruminants, and predators. At the same time, marine ecosystems reorganized – modern coral reef systems, teleost fish radiation, and the emergence of whales in the Eocene. There were no mosasaurs or other marine reptiles, so some niches were occupied by marine mammals (e.g., whales)."
"7. The significance of the K–Pg extinction"
"7.1 Confirmation of impact hypotheses"
"For decades, the iridium anomaly discovered by Alvarez sparked debate, but the discovery of the Chicxulub crater largely cleared uncertainties: a large asteroid impact can cause sudden global crises. The K–Pg event is an example of how an external cosmic force can abruptly change Earth's \"status quo\", rewriting ecological order."
"7.2 Understanding the dynamics of mass extinction"
"K–Pg boundary data help understand extinction selectivity: smaller, more generalized species or lifestyles survived, while large and highly specialized ones went extinct. This is relevant today when considering how biodiversity responds to rapid increases in climatic or environmental stressors."
"7.3 Cultural and scientific heritage"
"\u201cDinosaur extinction" has become deeply ingrained in the public imagination, becoming an archetypal image of a large meteorite ending the Mesozoic. This story shapes our understanding of the planet's fragility – and that a future large impact could pose a similar threat to modern life (although the near-term probability is low).
8. Future research directions and unanswered questions
- More precise chronology: High-precision dating to determine whether Deccan eruptions fully coincided with the extinction horizon.
- Detailed taphonomic study: How local fossil deposits reflect the duration of the process—sudden or multi-phase.
- Global darkness and fires: Studies of soot and carbon deposits will help refine the “impact winter” period.
- Recovery pathways: Paleocene communities show how survivors rebuilt ecosystems.
- Biogeographic models: Were there “refuges” in certain regions? Did survival depend on latitude?
9. Conclusion
The Cretaceous–Paleogene extinction highlights how an external shock (asteroid impact) combined with prior geological stress (Deccan volcanism) can together destroy a vast portion of biodiversity and wipe out even dominant groups—non-avian dinosaurs, pterosaurs, marine reptiles, and many marine invertebrates. The suddenness emphasizes nature's fragility in the face of intense catastrophes. After this extinction, surviving mammals and birds took over a drastically changed Earth, opening evolutionary lines that led to modern ecosystems.
Alongside its paleontological significance, the K–Pg event also resonates on a broader scale—in discussions of planetary threats, climate shifts, and mass extinctions. By unraveling the boundary clay and Chicxulub crater evidence, we increasingly understand how Earth's life can be both resilient and highly vulnerable at once, influenced by cosmic chance events and internal planetary processes. The extinction of the dinosaurs, though biologically tragic, opened evolutionary pathways for the Age of Mammals—and ultimately for us.
References and further reading
- Alvarez, L. W., Alvarez, W., Asaro, F., & Michel, H. V. (1980). “Extraterrestrial cause for the Cretaceous–Tertiary extinction.” Science, 208, 1095–1108.
- Schulte, P., et al. (2010). “The Chicxulub asteroid impact and mass extinction at the Cretaceous–Paleogene boundary.” Science, 327, 1214–1218.
- Hildebrand, A. R., et al. (1991). “Chicxulub Crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico.” Geology, 19, 867–871.
- Keller, G. (2005). “Impacts, volcanism and mass extinction: random coincidence or cause and effect?” Australian Journal of Earth Sciences, 52, 725–757.
- Courtillot, V., & Renne, P. (2003). “On the ages of flood basalt events.” Comptes Rendus Geoscience, 335, 113–140.
- Hull, P. M., et al. (2020). “On impact and volcanism across the Cretaceous-Paleogene boundary.” Science, 367, 266–272.