The impact of an asteroid approximately 66 million years ago marked the beginning of the Cretaceous-Paleogene (K-Pg) extinction event. This event led to the demise of non-avian dinosaurs through immediate devastation and prolonged environmental disruption.
The Initial Catastrophe
The asteroid, estimated to be about 10 to 15 kilometers in diameter, struck the Yucatán Peninsula. This collision released energy equivalent to billions of atomic bombs, vaporizing rock and excavating a massive crater over 180 kilometers wide. The blast generated a superheated air pulse that incinerated everything within hundreds of kilometers of the impact site.
A shockwave propagated outwards, causing widespread earthquakes and volcanic activity across the globe. Incandescent debris, ejected into the atmosphere, rained down, igniting widespread wildfires across continents. These fires consumed forests and grasslands, releasing massive amounts of smoke and soot into the atmosphere. The impact also triggered colossal tsunamis that devastated coastal regions thousands of kilometers away. Physical destruction and extreme heat rendered many areas uninhabitable within hours to days.
The Global Environmental Collapse
Beyond the immediate devastation, the asteroid impact triggered a prolonged environmental collapse. Billions of tons of dust, ash, and aerosols were ejected high into the atmosphere, forming a dense, global shroud. This atmospheric veil blocked sunlight, plunging Earth into prolonged darkness. This atmospheric blockage led to “impact winter,” causing global temperatures to plummet dramatically.
Photosynthesis, the foundation of most food webs, largely ceased as plants were deprived of sunlight. The collapse of primary producers quickly led to the starvation of herbivores, and subsequently, the carnivores that preyed upon them. Chemical reactions in the atmosphere, spurred by the impact, likely produced large amounts of sulfuric acid. This led to widespread acid rain, further damaging terrestrial and marine ecosystems. The combination of darkness, extreme cold, and acid precipitation created an environment profoundly hostile to most complex life forms, disrupting the delicate balance of ecosystems worldwide for months to years.
Pinpointing the Extinction Timeline
The scientific consensus indicates that the extinction of non-avian dinosaurs unfolded rapidly following the asteroid impact, rather than over millions of years. While the initial devastation was instantaneous, the full extinction process occurred over a period ranging from months to a few years. Geological evidence provides strong support for this swift timeline.
A distinct geological layer, known as the K-Pg boundary, marks this catastrophic event globally. This thin layer is rich in iridium, an element rare on Earth’s surface but abundant in asteroids, confirming the extraterrestrial origin of the impactor. Above this iridium-rich layer, non-avian dinosaur fossils abruptly disappear from the fossil record, indicating a near-simultaneous extinction.
Evidence of widespread wildfires, including charcoal layers found globally at the K-Pg boundary, further supports the rapid environmental disruption. Additionally, the “fern spike” observed in the fossil record immediately after the event suggests a period of ecological devastation followed by the rapid colonization of hardy fern species. These lines of evidence collectively point to a relatively swift and catastrophic extinction event that decimated complex ecosystems across the planet.
Survivors and the Dawn of a New Era
Despite the widespread destruction, some groups of life managed to survive the K-Pg extinction event. Avian dinosaurs, or birds, were among the survivors, alongside various small mammals, crocodiles, turtles, amphibians, and fish. Their ability to survive is often attributed to characteristics such as smaller body sizes, which required fewer resources, and the capacity to burrow or seek shelter from the immediate cataclysm. Many surviving species also had more generalized diets or were less reliant on specific plant types that perished during the impact winter. The decimation of the dominant non-avian dinosaurs created vast ecological niches that were previously unavailable. This major biological reset paved the way for the dramatic diversification and evolutionary success of mammals.