Sixty-six million years ago, an asteroid roughly the size of a small city smashed into Earth at around 45,000 miles per hour. The explosion was more powerful than a billion nuclear bombs. Within hours, a wall of fire spread across continents. Then a massive cloud of dust and debris rose into the upper atmosphere and blocked the sun — for years. Plants died. Animals that ate plants starved. Animals that ate those animals had nothing left. About 75% of all species on Earth were gone in what scientists now call the K-Pg extinction event.
That is why the dinosaurs disappeared. But here’s something surprising: not all of them did.
The kind you’re imagining — T. rex, Triceratops, Brachiosaurus — yes, those are gone. But one branch of dinosaurs survived the disaster. Their descendants are outside your window right now.
Key Takeaways
– A massive asteroid struck Earth 66 million years ago near present-day Mexico, triggering fires, darkness, and a collapse of the food chain.
– The impact created an “impact winter” — years of reduced sunlight that killed plants and starved large animals.
– About 75% of all species went extinct, including nearly all dinosaurs.
– Volcanic eruptions in India were already stressing the planet before the asteroid arrived, making survival even harder.
– Birds are living dinosaurs — one group of feathered dinosaurs survived and eventually became every bird species alive today.
What Exactly Hit the Earth?
The object was an asteroid (some scientists think it may have been a comet — the debate continues) measuring roughly 6 to 9 miles across. That might not sound like much. But size is less important than speed and force.
When it hit the shallow sea near what is now Mexico’s Yucatan Peninsula, it vaporized rock, ocean water, and everything for hundreds of miles in an instant. The force launched debris high enough to re-enter the atmosphere all around the planet, not just near the crash site.
Think of dropping a rock into a puddle. The splash goes in every direction. Now imagine the puddle is an ocean, and the splash reaches into space.
The impact site is called the Chicxulub crater (pronounced “cheek-shoo-loob”), named after a nearby town. It is about 110 miles wide, mostly buried beneath the Gulf of Mexico and the Yucatan Peninsula. You can’t see it from the ground, but scientists have drilled into it and pulled up melted rock, shocked quartz crystals (which only form under extreme pressure), and other unmistakable evidence of a world-changing impact.
The Three Stages of Disaster
The asteroid did not just explode and kill everything nearby. It set off a chain of events that played out over hours, years, and thousands of years.
Stage 1: The First Hours
Within minutes of impact, massive tsunamis spread across oceans. Superheated debris rained back down from the atmosphere like a planet-wide shower of fire, setting forests ablaze across continents. Animals thousands of miles from Mexico were in serious trouble almost immediately.
Ten-year-old Sofia asked her science teacher once why the dinosaurs near Mexico did not just “warn the others.” Her teacher explained: this was not like a local fire or a flood. The debris that the impact launched went so high it circled the entire Earth before falling back down. It was less like one disaster and more like the whole sky becoming a problem at once.
Stage 2: Impact Winter (The Following Years)
This is the part that truly finished most of the dinosaurs.
Dust, ash from wildfires, and sulfur particles from vaporized rock all rose into the upper atmosphere. Once material gets that high, it does not fall back quickly. It spreads around the planet and stays.
Scientists estimate that sunlight may have been significantly reduced for one to two years, possibly longer. Without sunlight, plants cannot grow. Without plants, plant-eating dinosaurs — the giant sauropods, Triceratops, Edmontosaurus, and hundreds of others — had nothing to eat.
Without plant-eaters, the meat-eaters had nothing to hunt either. T. rex, one of the most powerful predators that ever lived, could not hunt what no longer existed.
The food chain collapsed from the bottom up.
Stage 3: Long-Term Climate Swings (Decades and Beyond)
After the initial darkness came dramatic temperature swings. The planet cooled sharply while sunlight was blocked, then warmed as gases stayed trapped in the atmosphere. This kind of rapid climate instability was deadly for large animals that needed stable food sources and temperatures to survive.
Smaller animals — early mammals, some reptiles, insects, birds — could eat seeds, insects, and scraps that survived in the soil. They could hide in burrows. The large ones had no such options.
Were Volcanoes Part of It Too?
Yes, and this part of the story is often left out.
At roughly the same time as the asteroid impact, enormous volcanic eruptions were happening in what is now India. Scientists call the region the Deccan Traps — an ancient lava field covering about 200,000 square miles. These eruptions poured carbon dioxide and sulfur dioxide into the atmosphere for hundreds of thousands of years before the asteroid arrived.
Many researchers now believe that dinosaurs were already struggling before the asteroid hit. The volcanic activity had been shifting the climate and stressing ecosystems for a long time. The asteroid, then, was the final blow against a world already weakened.
Picture it this way: if you have not slept well for a week and already feel sick, even a regular cold hits harder. The dinosaurs were dealing with a long illness. The asteroid was the knockout punch.
How Do Scientists Know Any of This?
None of it was witnessed. Humans and non-avian dinosaurs were separated by about 65.9 million years. So how do scientists know what happened?
The Iridium Layer
In the late 1970s, geologist Walter Alvarez was studying rock layers in Gubbio, Italy, when he noticed something odd. Right at the boundary between the Cretaceous period (age of dinosaurs) and the Paleogene period (age of mammals), there was a thin layer with unusually high levels of a metal called iridium.
Iridium is rare near Earth’s surface. But it is common in asteroids.
Alvarez and his father, physicist Luis Alvarez, tested the same boundary layer at sites around the world — Italy, Denmark, New Zealand, Spain, North America. Every single location had the same iridium spike. There was only one explanation that made sense: an asteroid had hit Earth and spread iridium across the entire planet.
Their paper, published in 1980, changed everything. NASA and researchers worldwide have since confirmed and expanded this finding.
The Chicxulub Crater
The actual crater was not confirmed until 1991, when scientists pieced together geological data from the Yucatan Peninsula and the Gulf of Mexico. Drilling expeditions since then have recovered evidence that places the impact precisely at the K-Pg boundary — the exact moment in Earth’s rock record when the dinosaurs vanish.
For a deep look at how scientists read Earth’s rock layers and atmospheric history, Smithsonian’s Ocean portal on mass extinctions is one of the best explainers available.
Did ALL Dinosaurs Actually Disappear?
No. This is the part that changes how you see birds.
Dinosaurs split into two main groups: non-avian dinosaurs (T. rex, Velociraptor, Stegosaurus — the classic ones) and avian dinosaurs, which had feathers and eventually became birds. The asteroid killed the non-avian dinosaurs completely. But some avian dinosaurs survived.
Why did they make it? Scientists think several things helped:
- They were small enough to survive on limited food
- They could fly to search large areas for seeds and insects
- Seeds buried in soil could survive the impact winter and sprout again when light returned
- Their hollow bones and feathers may have made them more adaptable
Over millions of years, those survivors diversified into every bird species alive today. There are roughly 10,500 bird species on Earth right now. Every single one of them is a living dinosaur.
So when someone says “dinosaurs are extinct,” you can tell them: there are more species of dinosaurs alive today than there are species of mammals.
Why Does Any of This Matter to Us?
Because you exist because of it.
When the non-avian dinosaurs disappeared, the small mammals that had been hiding in the shadows for millions of years finally had space to grow, spread, and evolve. Without giant predators competing for every resource, mammals diversified rapidly. Over tens of millions of years, that led to primates, then apes, then humans.
If the asteroid had missed, or arrived a few million years earlier or later, dinosaurs might still dominate the planet. Mammals would likely have stayed small and hidden. There would be no humans standing in museums, looking up at T. rex skeletons, asking why they are gone.
The question carries its own answer. We are here to ask it because the asteroid happened.
Questions Kids Actually Ask
Why didn’t the dinosaurs just move to a safer place?
There was no safe place. The disaster was not local. Fires, darkness, and the collapse of the food chain happened across the whole planet within hours and years. No dinosaur could outrun climate change spreading worldwide.
Could an asteroid like this hit Earth again?
Technically, yes. But NASA and other space agencies now track large near-Earth asteroids. No object that size is currently on a collision course with Earth. And unlike the dinosaurs, humans could potentially see one coming far enough in advance to do something about it.
How do we know what dinosaurs looked like if they are all gone?
Fossils. When animals die in the right conditions, their bones slowly turn to rock over millions of years. Scientists dig these up and study them. Some fossils even preserve impressions of skin or feathers, which is how we know many dinosaurs were feathered.
What else went extinct with the dinosaurs?
Quite a lot. About 75% of all species disappeared, including mosasaurs, plesiosaurs, pterosaurs, ammonites, and many types of plants and marine life. Animals that survived tended to be small, able to eat a variety of foods, or capable of going dormant (like seeds or eggs).
How big was the asteroid compared to something I know?
At 6 to 9 miles wide, the Chicxulub asteroid was roughly the length of Manhattan Island. Moving at 45,000 miles per hour, the energy it released was estimated at over a billion times more powerful than the atomic bomb dropped in 1945.
Watch: The Impact, Explained
Search YouTube for “Chicxulub asteroid impact animated” and you will find several excellent videos that show the scale of the explosion, the debris field, and the impact winter in ways that words struggle to capture. The Natural History Museum and PBS Eons both have strong, accurate versions.
So Why Did the Dinosaurs Disappear?
A rock from space hit at the worst possible angle, in the worst possible location, on a planet already under stress from volcanic activity. It set off fires, then darkness, then starvation. The largest animals on Earth had no way to adapt fast enough. Most of them died within years.
But the story did not end there. Small survivors rebuilt. Mammals spread. Birds — the dinosaurs that made it — diversified across every continent. Eventually, curious creatures called humans arrived, found bones in the ground, and started asking questions.
The ones who made it through were not the biggest or the strongest. They were the smallest, the most adaptable, and sometimes just the luckiest. That is a lesson that goes well beyond dinosaurs.
If you want to keep exploring Earth’s big moments, our history for kids section covers everything from ancient civilizations to scientific discoveries. And since the impact winter was really a story about Earth’s atmosphere, what the atmosphere actually is is worth reading next — it makes the whole disaster make more sense.
