The disappearance of dinosaurs around 66 million years ago has long captivated scientific inquiry. Scientific consensus points to a single, catastrophic event as the primary driver of this mass extinction. This event reshaped Earth’s ecosystems, leading to the demise of numerous life forms and paving the way for the rise of new species.
The Impact Event
Approximately 66 million years ago, an asteroid about 10 kilometers (6.2 miles) in diameter struck Earth. It collided at about 20 kilometers per second, impacting the Yucatán Peninsula in what is now Mexico. The collision released explosive energy equivalent to approximately 100 teratons of TNT, billions of times more powerful than the Hiroshima atomic bomb.
The impact created a cavity about 100 kilometers (62 miles) wide and 30 kilometers (19 miles) deep, blasting an estimated 25 trillion metric tons of molten material into the atmosphere. Superheated winds exceeding 1,000 kilometers per hour (620 mph) radiated outwards, incinerating vegetation and killing animals. This initial shockwave also generated massive tsunamis that swept across coastal regions, particularly in the Gulf of Mexico and Caribbean, and triggered widespread wildfires globally.
Worldwide Catastrophe and Extinction
The impact’s immediate destruction led to global, long-term environmental devastation. Volume of dust, soot, and sulfurous materials ejected into the atmosphere created a “nuclear winter-like effect”. This dense atmospheric veil blocked sunlight for months or years, drastically reducing global temperatures and halting photosynthesis.
The impact also unleashed widespread acid rain, as ejected sulfates and water vapor combined to form sulfuric acid. The oceans experienced a significant drop in pH, leading to ocean acidification. This change in acidity severely impacted marine calcifiers, organisms that build shells and skeletons from calcium carbonate, which are foundational to marine food webs. The disruption of photosynthesis, both on land and in the oceans, caused food chains to collapse, leading to the extinction of approximately 75% of all plant and animal species on Earth, including all non-avian dinosaurs, pterosaurs, and marine reptiles like mosasaurs and plesiosaurs. While many large animals perished, some species, such as sea turtles, crocodilians, and certain mammals and birds, managed to survive by burrowing or adapting to the harsh conditions.
Unearthing the Evidence
Geological evidence supports this catastrophic event. A thin layer of clay, known as the Cretaceous-Paleogene (K-Pg) boundary, is found globally in rock formations. This boundary layer contains an abnormally high concentration of iridium, an element rare in Earth’s crust but common in asteroids. The Alvarezes, a father and son team, first popularized this discovery in 1980, finding iridium levels up to 160 times above background in a clay layer in Italy.
Additional evidence includes shocked quartz and tektites within this boundary layer. Shocked quartz grains form under extreme pressure, characteristic of an impact event, while tektites are small glass beads created from melted rock ejected during the collision. The Chicxulub crater was identified in the late 1970s by geophysicists Antonio Camargo and Glen Penfield during petroleum exploration in the Yucatán Peninsula. Geophysical surveys and drilling projects later confirmed the buried, circular structure, estimated to be 180-200 kilometers (110-120 miles) in diameter and 20-30 kilometers (12-19 miles) deep, directly linking it to the K-Pg boundary event.
Debate and Scientific Consensus
While the Chicxulub asteroid impact is widely accepted as the primary cause of the K-Pg extinction, alternative theories have been considered. An alternative is the Deccan Traps volcanism in India, a period of immense volcanic activity. These eruptions released large quantities of carbon dioxide and sulfur into the atmosphere, which could have contributed to climate change.
The main phase of Deccan Traps volcanism began hundreds of thousands of years before the Chicxulub impact and continued afterward, suggesting it was a contributing factor rather than the sole cause. Scientific consensus holds that the timing and scale of the Chicxulub impact’s effects align precisely with the extinction event, indicating it was the main catalyst. The asteroid impact likely delivered a sudden, overwhelming blow that pushed Earth’s ecosystems beyond their breaking point, while ongoing volcanism may have further stressed the environment.