Three-quarters of all species on Earth were eliminated in a single moment
Sixty-six million years ago, a mountain-sized asteroid ended an era — striking the Yucatan Peninsula with a force that darkened skies, collapsed food chains, and erased three-quarters of all life on Earth. The Chicxulub crater it left behind is not merely a geological scar but a reminder that planetary life is fragile, contingent, and subject to forces far beyond any species' control. The extinction of the non-avian dinosaurs, dominant for 165 million years, cleared the way for the mammals whose descendants would eventually ask why it happened.
- A 10–15 km asteroid struck shallow Mexican waters with the energy of billions of nuclear weapons, carving a 180 km crater in an instant.
- Dust and debris blanketed the atmosphere, blocking sunlight for months, collapsing photosynthesis, and unraveling every food chain on the planet.
- Triceratops, Tyrannosaurus, pterosaurs — species that had ruled land and sky for over 165 million years — vanished in the cascading darkness and cold.
- Three-quarters of all Earth's species were eliminated, yet small mammals and avian dinosaurs survived, inheriting a world suddenly emptied of its giants.
- Scientists now probe whether the dinosaurs were already weakened by volcanism and climate stress before impact — raising the unsettling question of whether the asteroid finished what the Earth had already begun.
Sixty-six million years ago, an asteroid between ten and fifteen kilometers wide descended through Earth's atmosphere and struck the shallow waters off Mexico's Yucatan Peninsula. The force of the collision carved a crater nearly two hundred kilometers across and released energy equivalent to billions of nuclear weapons detonating at once. Rock vaporized, tsunamis swept across oceans, and a vast cloud of dust and debris rose into the atmosphere, blocking sunlight for months. Temperatures plummeted, photosynthesis ceased, and the food chains sustaining life from the smallest organisms to the largest predators collapsed in sequence.
The dinosaurs, which had thrived for roughly 165 million years, could not survive what followed. The sudden darkness, the cold, the absence of vegetation proved incompatible with the physiology of the great reptiles. Triceratops, Tyrannosaurus rex, and the pterosaurs all disappeared. Only birds — themselves a lineage of dinosaurs — endured and continued evolving into the avian diversity we know today. The extinction was indiscriminate: marine reptiles, most mammals, amphibians, plants, and insects all suffered catastrophic losses. Three-quarters of all species on Earth were eliminated in what geologists call the Cretaceous-Paleogene extinction event.
Yet the story may be more complicated than a single moment of cosmic violence. Scientists continue to investigate whether volcanic activity, climate shifts, and rising sea levels had already weakened dinosaur dominance in the millions of years before impact. Some evidence suggests the asteroid may have delivered a final blow to a lineage already under strain. The question remains open — were the dinosaurs undone by the cosmos alone, or were they already falling when the sky fell on them?
Sixty-six million years ago, a space rock the size of a mountain descended through Earth's atmosphere and struck the shallow waters off Mexico's Yucatan Peninsula. The asteroid, between ten and fifteen kilometers wide, hit with such force that it carved a crater nearly two hundred kilometers across into the bedrock below. The impact was not merely a local catastrophe. What followed was a cascade of destruction that reshaped the entire planet—a mass extinction event so severe that it erased three-quarters of all living species from existence, including every non-avian dinosaur that had dominated terrestrial ecosystems for over a hundred million years.
The crater left behind, now called Chicxulub, stands as one of the most consequential scars in Earth's geological record. When the asteroid struck, it released energy equivalent to billions of nuclear weapons detonating simultaneously. The collision vaporized rock, sent tsunamis racing across oceans, and ejected so much dust and debris into the atmosphere that sunlight was blocked from reaching the surface for months or longer. Temperatures plummeted. Photosynthesis ceased. The food chains that sustained life—from the smallest organisms to the largest predators—collapsed in sequence.
The dinosaurs, which had thrived for roughly 165 million years, could not survive what came next. The sudden darkness, the cold, the absence of vegetation—these conditions were incompatible with the physiology and ecology of the great reptiles. Species after species went extinct. Triceratops vanished. Tyrannosaurus rex disappeared. The pterosaurs, which had ruled the skies, were gone. Only the birds, themselves a lineage of dinosaurs, survived the extinction and continued evolving into the diverse avian species we see today.
But the asteroid impact did not stop at dinosaurs. The extinction was indiscriminate in its scope. Marine reptiles perished. Most mammals died, though some small populations survived to eventually diversify and fill the ecological niches left empty. Amphibians, fish, insects, and plants all suffered catastrophic losses. Three-quarters of all species on Earth—a staggering proportion—were eliminated in what geologists call the Cretaceous-Paleogene extinction event, marking the boundary between two geological epochs.
Yet the story of the dinosaurs' demise may be more complicated than a single moment of cosmic violence. Scientists continue to investigate whether the dinosaurs were already in decline before the asteroid arrived, whether environmental pressures and ecological stress had weakened their dominance. Some evidence suggests that volcanic activity, climate change, and shifting sea levels in the millions of years before impact may have already pushed many species toward extinction. If true, the asteroid did not so much cause the extinction as deliver the final blow to a lineage already struggling to adapt. The question remains open: were the dinosaurs doomed by the cosmos, or were they already falling when the sky fell on them?
Citas Notables
Scientists continue investigating whether dinosaurs faced environmental pressures before impact, suggesting complex extinction mechanisms— Scientific research on pre-impact conditions
La Conversación del Hearth Otra perspectiva de la historia
When you say the asteroid was ten to fifteen kilometers wide, what does that actually mean for someone trying to picture it?
It's roughly the distance across a major city. Imagine something the size of a metropolitan area hurtling through space at tens of kilometers per second. When it hit, the energy released was so enormous that it didn't just create a crater—it fundamentally altered the chemistry of the atmosphere.
And the crater itself, the Chicxulub—is that still visible today?
Yes, though not as a dramatic hole. It's buried under sediment and water, but geologists can map it through gravity measurements and drilling. The rim is still detectable. It's become one of the most studied impact sites on Earth precisely because it marks such a turning point.
You mentioned that three-quarters of species died. Does that mean one-quarter survived?
Exactly. Some organisms made it through—certain fish, some amphibians, small mammals, insects. The survivors were often those that could shelter underground, in water, or in other protected spaces. And they inherited a world with almost no competition, which allowed them to diversify rapidly over millions of years.
But you also said dinosaurs might have been struggling before the impact. How do scientists know that?
Fossil records show declining diversity in some dinosaur lineages in the millions of years before impact. There's also evidence of volcanic activity and climate shifts during that period. So the question becomes: did the asteroid finish off a group already in trouble, or would they have survived without it?
Which explanation do most scientists lean toward now?
There's genuine debate. The impact was certainly catastrophic enough to cause extinction on its own. But the evidence for pre-existing stress is real too. The most honest answer is that it was probably both—a species or group weakened by environmental change, then struck by an extinction-level event.