Did a single asteroid strike 66 million years ago end the age of dinosaurs?

Nature · Published 3 October 2026 Swipe more like this →

In short: For decades, scientists debated whether volcanoes or an extraterrestrial impact caused the mass extinction of the dinosaurs. A breakthrough discovery of a rare metal in Italian limestone led to a revolutionary theory, eventually confirmed by a massive crater buried beneath the seafloor, forever changing our understanding of Earth's history.

The story began in 1977, when geologist Walter Alvarez was studying limestone near Gubbio, Italy. He noticed a mysterious thin layer of red clay separating the Cretaceous and Tertiary periods. This boundary marked a biological desert where nearly 75 percent of all species, including dinosaurs, vanished. Curious about the timeline of this extinction, Walter enlisted his father, Nobel laureate physicist Luis Alvarez, and chemists Frank Asaro and Helen Michel. Using neutron activation analysis, they discovered the clay contained iridium concentrations 600 times higher than normal. Since iridium is rare on Earth but common in asteroids, they proposed that a massive space rock had collided with our planet.

The 1980 hypothesis faced intense skepticism, with many critics arguing that volcanic activity, specifically the Deccan Traps in India, was the true culprit. However, the discovery of shocked quartz and microtektites globally provided evidence of a violent impact. The debate was effectively settled in 1991 with the identification of the Chicxulub crater off the Yucatan Peninsula. Measuring 180 kilometers wide and 20 kilometers deep, the site confirmed the scale of the cataclysm. In 2010, an international panel of 41 experts formally endorsed the asteroid theory, concluding that the impact released energy thousands of times greater than the world's nuclear arsenal.

Recent research has refined the details of this event. While early estimates placed the impact at 65 million years ago, modern dating suggests it occurred 66 million years ago. A 2016 drilling project into the crater's peak ring revealed that the impact vaporized local gypsum, likely injecting climate-altering aerosols into the atmosphere. Further evidence, such as fossilized fish in North Dakota containing impact debris, suggests the event triggered massive water displacement and rapid burial. This singular, violent collision not only ended the reign of the dinosaurs but fundamentally reshaped the trajectory of life on Earth, clearing the path for the rise of mammals.

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