The sudden silence of a 230-million-year reign
In short: For over two centuries, dinosaurs dominated the Earth's landscapes. Then, in a geological blink of an eye, they vanished. While some species were already in decline, a catastrophic event triggered a mass extinction that wiped out three-quarters of all life on the planet.
The end of the Cretaceous Period, approximately 66 million years ago, marks one of the most dramatic biological shifts in Earth's history. For at least 230 million years, dinosaurs thrived in diverse forms, evolving to meet changing environments. However, the fossil record shows a sudden cessation of nonavian dinosaur remains in rocks younger than 66 million years. This transition to the Paleogene period saw the collapse of entire ecosystems, including the disappearance of pterosaurs, ammonites, and massive marine reptiles like mosasaurs and plesiosaurs.
The prevailing scientific debate centers on whether this was a result of 'interplanetary violence' or 'Earthly woes.' The Alvarez hypothesis, proposed in 1980 by Luis and Walter Alvarez, suggests a mountain-sized meteor struck the Earth. Their evidence lies in the K-Pg boundary—a geologic layer containing unusually high levels of iridium, a metal rare in Earth's crust but common in meteorites.
This theory was bolstered by the discovery of the Chicxulub crater in Mexico's Yucatán Peninsula. Measuring about 93 miles wide, the crater's impact would have vaporized rock and sent gases into the atmosphere, creating environmental effects that persisted for years. However, the extinction may not have been a single-bullet event. Some evidence suggests that large-scale volcanic eruptions caused significant climate change, potentially working in tandem with more gradual environmental shifts occurring over millions of years. While the number of dinosaur species was already declining, these catastrophic factors likely moved faster than the creatures could adapt. This cleared the ecological stage, allowing the only surviving dinosaurs—birds—and various mammals to undergo rapid evolution and fill the resulting gaps in the global ecosystem.
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Sources
- Summary by Intellect · source: Why Did Dinosaurs Go Extinct? | Dinosaur Extinction Explained
- Also: Why did the dinosaurs go extinct?
- Also: What killed the dinosaurs? | Natural History Museum
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