Asteroid impact and volcanic activity caused the extinction of non-avian dinosaurs
End of an era
More than 150 million years dinosaurs dominated terrestrial ecosystems, while reptiles such as mosasaurs, plesiosaurs, and in the sky – pterosaursThis long streak of Mesozoic success suddenly ended 66 million years ago, at Cretaceous–Paleogene (K–Pg) boundary (formerly known as the "K–T" boundary). In a relatively short geological interval, non-avian dinosaurs, large marine reptiles, ammonites, and many other species became extinct. The surviving groups—birds (avian dinosaurs), mammals, some reptiles, and selected parts of the marine fauna—inherited a dramatically changed world.
At the center of this K–Pg extinction is Chicxulub impact – catastrophic ~10–15 The impact of a 1000-km-diameter asteroid or comet in the region of what is now the Yucatán Peninsula. Geological evidence strongly supports this cosmic event as the primary cause, although volcanic eruptions (so-called Dean's Stairs In India, additional stresses from greenhouse gases and climate change contributed. This combination of events brought about the end of many Mesozoic lineages, making it the fifth major mass extinction. Understanding this event allows us to see how sudden, widespread shocks can disrupt even seemingly invincible ecological dominance.
2. Chalk World Before Impact
2.1 Climate and biota
Late Cretaceous (~100–66) During the period (100 million years ago) when the Earth was relatively warm, high sea levels flooded the interior of the continents, forming shallow epicontinental seas. Angiosperms (flowering plants) flourished, creating a variety of terrestrial habitats. Dinosaur faunas included:
- Theropods: Tyrannosaurs, dromaeosaurs, abelisaurs.
- Ornithischians: Hadrosaurs ("anterosaurs"), ceratopsians (Triceratops), ankylosaurs, pachycephalosaurs.
- Sauropods: Titanosaurs, especially in the 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 seemed stable and viable, right up to the K–Pg boundary.
2.2 Deccan Traps volcanism and other stressors
In the Late Cretaceous, giant fossils began to appear on the Indian subcontinent. Dean's Stairs eruptions. These basaltic eruptions released CO2, sulfur dioxide, aerosols, possibly warming or acidifying the environment. While this alone may not have been enough to cause the extinction, it could have weakened ecosystems or had a gradual climate impact, preparing for something even more drastic [1], [2].
3. Chicxulub Impact: Evidence and Mechanism
3.1 Discovery of the iridium anomaly
1980 Luiz Alvarez with co-authors discovered iridium-rich clay layer at the K–Pg boundary in Gubbio, Italy, and other points. Since iridium is rare in the Earth's crust but more abundant in meteorites, they suggested that a large impact was the cause of this extinction. This layer has also been described by others impact indicators:
- Impact quartz (shocked quartz).
- Microtektites (small glass spherules formed during the evaporation of rocks).
- High concentration of platinum group elements (e.g. osmium, iridium).
3.2 Crater location: Chicxulub, Yucatan
Subsequent geophysical surveys have detected ~180 km diameter crater (Chicxulub Crater) under the Yucatan Peninsula in Mexico.It corresponds exactly to ~10–15 km diameter asteroid/comet impact: there are signs of impact metamorphism, gravitational anomalies, boreholes reveal layers of weathered rock. Radiometric dating of these rocks coincides with the K–Pg boundary (~66 million years ago), thus definitively proving the connection between the crater and the extinction [3], [4].
3.3 Impact dynamics
During the collision, kinetic energy equivalent to billions of atomic bombs was released:
- Shock wave and discharge: Rock vapor and soluble fragments rose to the upper atmosphere, possibly falling on a global scale.
- Fires and heat wave: Global fires could have been ignited by returning ejecta fragments or superheated air.
- Abundance of dust and aerosols: Fine particles blocked sunlight, drastically reducing photosynthesis during a "shock winter" of several months or years.
- Acid rain: Sulfur and CO were released during the evaporation of anhydrite or carbonate rocks2, causing acid rain effects and climate perturbations.
The combination of these short-term darkness/cold and long-term greenhouse effects caused widespread damage to terrestrial and marine ecosystems.
4. Biological shock and selective extinctions
4.1 Terrestrial losses: non-avian dinosaurs, etc.
Non-avian dinosaurs, from apex predators, e.g. Tyrannosaurus rex, to giant herbivores, such as Triceratops, disappeared completely. Pterosaurs also died out. Many smaller land animals that depended on large plants or stable ecosystems suffered great losses. However, certain lineages survived:
- Birds (avian dinosaurs) – perhaps survived due to smaller size, seed-based diet, and more flexible diet.
- Mammals: Also suffered, but recovered more quickly and quickly evolved into larger forms in the Paleogene.
- Crocodiles, turtles, amphibians: Aquatic/semi-aquatic groups also managed to survive.
4.2 Marine extinctions
Extinct in the oceans mosasaurs and plesiosaurs, and along with them many invertebrates:
- Ammonites (long-lived cephalopods) became extinct, although nautiluses survived.
- Planktonic foraminifera and other microfossil groups, important in marine food webs, were severely affected.
- Corals and bivalves suffered partial or local extinctions, but certain lineages recovered.
The decline in primary production during the “shock winter” probably starved marine food webs. Species less dependent on constant production or able to feed on detritus survived better.
4.3 Survival models
Smaller, more generalist species that could feed flexibly or adapt more often survived, while larger or highly specialized creatures went extinct. This "selectivity" of size/ecological specialization may indicate that a combination of extreme environmental changes (darkness, fires, greenhouse) disrupted the entire established chain.
5. The role of Deccan Trap volcanism
5.1 Time coincidence
Dean's Stairs In India, eruptions leave extensive basaltic layers dating to the K–Pg boundary, releasing huge amounts of CO2 and sulfur levels. Some scientists believe that this alone could have been enough to trigger major environmental crises, perhaps in the form of warming or acidification. Others believe that this volcanism became a major stressor, but the main "death blow" was dealt by the Chicxulub cosmic body.
5.2 Joint effects hypothesis
It is often argued that the Earth was already "stressed" by the Deccan eruptions - with possible warming or partial disruption of ecosystems - when the Chicxulub impact finally destroyed everything. This model of interaction explains why the extinction was so total: several factors combined to overwhelm the resilience of ecosystems [5], [6].
6. Consequences: A New Age of Mammals and Birds
6.1 Paleogene world
After the K–Pg boundary, the surviving groups expanded rapidly during the Paleocene epoch (~66–56 million (year):
- Mammals expanded into vacant niches previously occupied by dinosaurs, transitioning from small, perhaps nocturnal forms to a variety of sizes.
- Birds branched out, occupying niches ranging from flightless land birds to aquatic specialized forms.
- Reptiles – crocodiles, turtles, amphibians and lizards – survived or diversified in the new, vacant habitats.
Thus, the K–Pg event acted as an evolutionary "reboot" similar to other mass extinctions. The foundations of today's terrestrial biota developed through newly constructed ecosystems.
6.2 Long-term climate and diversity trends
During the Paleogene, the Earth's climate gradually cooled (after a brief Paleocene–Eocene thermal maximum), which led to the further development of mammals, eventually leading to the emergence of primates, ungulates, and predators. At the same time, marine ecosystems underwent reorganization, with the emergence of modern coral reef systems, the radiation of teleost fish, and the emergence of whales in the Eocene. There are 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 Validation of impact hypotheses
For decades, the iridium anomaly discovered by Alvarez was controversial, but the discovery of the Chicxulub crater largely cleared up the confusion: large asteroid impact can cause sudden global crises. The K–Pg event is an example of how an external cosmic force can abruptly change the Earth's "status quo", rewriting the ecological order.
7.2 Understanding the dynamics of mass extinctions
The K–Pg boundary data help us understand the selectivity of extinction: smaller, more generalized species or lifestyles survived, while large and highly specialized ones went extinct. This is still relevant today, when considering how biodiversity responds to rapid increases in climatic or environmental stressors.
7.3 Cultural and scientific heritage
"Dinosaurs The “extinction” has become deeply embedded in the public imagination, becoming the 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 likelihood is remote in the near future).
8. Future research directions and unanswered questions
- More precise chronology: High-precision dating to determine whether the Deccan eruptions coincided exactly with the extinction horizon.
- A detailed study of taphonomy: How local fossil deposits reflect the duration of the process – whether it was sudden or made up of several phases.
- Total eclipse and fires: Studies of soot and carbon deposits will help to clarify the period of the "impact winter".
- Paths to recovery: Paleocene communities show how survivors restored ecosystems.
- Biogeographic models: Were there "refugees" in certain regions? Did survival depend on latitude?
9.Conclusion
Cretaceous–Paleogene extinction event highlights how external impact (asteroid impact) and earlier geological stress (Deccan volcanism) combined to wipe out a large part of biodiversity and even kill off the dominant groups – non-avian dinosaurs, pterosaurs, marine reptiles and many marine invertebrates. The suddenness highlights the fragility of nature in the face of intense cataclysms. After this extinction, mammals and birds that survived took over a greatly changed Earth, opening the evolutionary lines that led to modern ecosystems.
Beyond its paleontological significance, the K–Pg event resonates in broader discussions of planetary threats, climate change, and mass extinctions. As we unravel the evidence from the boundary clay and the Chicxulub crater, we increasingly understand how life on Earth can be both resilient and highly vulnerable, affected by cosmic accidents and internal planetary processes. The demise of the dinosaurs, while biologically tragic, paved the evolutionary path for the Age of Mammals—and ultimately for us.
References and further reading
- Alvarez, LW, Alvarez, W., Asaro, F., & Michel, HV (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, AR, 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." Geoscience Reports, 335, 113–140.
- Hull, P.M., et al. (2020). "On impact and volcanism across the Cretaceous-Paleogene boundary." Science, 367, 266–272.