Your turn
Each lab is one step from the video. Change things and see what happens.
Each lab isolates one part of the story. The models are simplified to show the idea.
Tap the buttons and slide the sliders.
Drag through the year. When do dinosaurs appear, vanish, and when do people show up?
Map the USGS calendar analogy: how much of the story came after the extinction?
Slide along the year. When are the dinosaurs here?
Tap each layer. What does each one tell us?
Which evidence in the boundary clay points to an impact?
Tap a stripe of rock. What is inside?
Drop the asteroid in both places. Which throws up more rock?
Compare a shallow-shelf strike with a deep-water strike.
A simplified side view, not to scale. Based on the Natural History Museum’s explanation.
Drag the timeline. What falls first, and what comes back first?
Follow sunlight, producers and consumers through the impact winter.
Slide the time. Watch the sky get dark, then bright again.
A sketch of the pattern, not measured data. How long the darkness lasted is still debated.
Slide the body size. Which animals had a chance?
Where does the land-animal survival ceiling fall, and who sits on each side?
Slide from tiny to giant. Who made it?
Being under 25 kg was a ceiling, not a guarantee: some small animals died too.
Drag through time. When did birds appear? When did big mammals come?
Place the extinction, the first bird-like fossils and big mammals on one timeline.
Slide along. Where are the birds?
Long, long ago, big dinosaurs lived all over the Earth. They lived here for a very long time. Then the big dinosaurs were gone. What happened?
Scientists found a thin stripe of clay in very old rocks. Under the stripe there are dinosaur bones. Over it, there are no dinosaurs at all, except birds. The clay has a special metal that comes from space rocks!
A huge space rock hit the Earth, far away in Mexico. It left a giant hole in the ground. Lots of dust went up into the sky.
The dust spread all around the world. The sky got dark and chilly. Plants need sunshine to grow, so they got weak. The big dinosaurs could not find enough food.
Small animals had a better chance. Turtles, crocodiles, frogs, lizards and tiny furry mammals made it. Plant seeds waited in the ground until the sky cleared up.
About 66 million years ago, an asteroid more than 10 kilometers wide slammed into Earth where Mexico's Yucatán Peninsula is today.17 The blast itself destroyed everything nearby, but the thing that killed dinosaurs worldwide was what it threw into the sky: soot, dust and hundreds of billions of tons of sulfur.9 That haze dimmed the Sun and cooled the planet. Plants struggled to grow, so plant-eating dinosaurs starved, and then the meat-eaters that hunted them starved too.18
About three out of every four species on Earth disappeared, including every dinosaur that wasn't a bird. Some bird lines survived, and their descendants are the birds we see today.16 Scientists call it the Cretaceous–Paleogene (K–Pg) mass extinction, and you'll also see it called the K–T extinction.13
The non-bird dinosaurs died out 66.0 million years ago, at the end of the Cretaceous Period. Older books say 65 million years, but newer dating of the rock layers has pinned it down more precisely.16 Before that, dinosaurs had ruled the land for about 165 million years.4
Deep time is hard to picture, so the U.S. Geological Survey suggests a trick. Squeeze all the time from the first dinosaurs to today into one calendar year. Dinosaurs appear on January 1, vanish in the third week of September, and people only turn up on December 31.4 That's why people and non-bird dinosaurs never met: nearly 65 million years separate them.5
The case was cracked like a detective story, and the first clue was a stripe of clay.
The Alvarez idea was controversial at first. Today it's the most widely accepted explanation.1
| Measurement | Best estimate |
|---|---|
| Asteroid width | More than 10 km (estimates run from about 10 to 15 km)17 |
| Speed | More than 25 km every second7 |
| Crater width | About 150 to 200 km1137 |
| Energy | Roughly 10 billion World War II atomic bombs9 |
| Sulfur blasted into the air | At least 325 billion metric tons9 |
The asteroid hit a shallow sea. The impact set off a blast wave and a heat wave, started wildfires thousands of miles away, and sent a giant tsunami that reached as far inland as today's Illinois.19 One study suggests that if it had arrived a few minutes later and landed in deeper water, it would have thrown up much less rock, and the extinction might not have happened.1
Fires and falling hot debris reached thousands of miles from the crater, but the blast alone can't explain a dinosaur dying in Mongolia, on the other side of the world. As one of the scientists who drilled into the crater put it, "the only way you get a global mass extinction like this is an atmospheric effect."9 Here's the chain of events:
How long did the darkness last? Scientists still debate that. Dust falls out of the air within weeks to a few years, while the sulfur haze may have lingered from a few years to several decades; that is still debated.814 Either way, it was long enough to break food chains on land and at sea.
Not on their own, but they probably didn't help. In what is now India, enormous eruptions called the Deccan Traps poured out lava on and off for about two million years. Their gases were already changing the climate before the asteroid arrived.113 The Natural History Museum's dinosaur expert sums it up like this: dinosaurs were living through a time of environmental change, and "the asteroid was the final, killer blow."1
The survivors were mostly small. On land, no animal heavier than about 25 kilograms (55 pounds) made it through.1 Turtles, crocodiles, lizards and snakes were hardly affected, and amphibians and mammals got off fairly lightly too.13 Plants fared better than animals because their seeds and pollen can wait out hard times. Afterwards, flowering plants took over.1
The losers included all the non-bird dinosaurs, the pterosaurs, big marine reptiles and the coiled-shell ammonites.12 With the giants gone, mammals got their chance. Still, it took about 15 million years before really big, rhino-sized mammals appeared.1
Birds evolved from theropods, the same group of meat-eating dinosaurs that Tyrannosaurus rex belonged to. The oldest bird-like fossils are more than 150 million years old and looked a lot like small feathered dinosaurs with teeth.3 When the asteroid hit, some bird lines survived, probably thanks to their small size, their ability to eat many kinds of food, and flight.3 Today there are at least 11,000 bird species.3 So all the non-bird dinosaurs are extinct, but every pigeon, penguin and chicken is a living dinosaur.1
About 66 million years ago, an asteroid more than 10 km wide hit what is now Mexico. It threw soot, dust and sulfur high into the sky, which dimmed the Sun and cooled the planet. Plants struggled, plant-eaters starved, then meat-eaters starved too. The Deccan Traps volcanoes in India were already stressing the climate.
An asteroid (a big space rock) at least 10 km wide. It left the Chicxulub crater, 150 to 200 km across, now buried under the Yucatán Peninsula and the seafloor off Mexico. The crater is exactly the same age as the extinction.
About 66 million years ago, at the end of the Cretaceous Period. Older books say 65 million years; newer dating has refined it to 66.0 million years ago.
There were no humans yet. People appeared nearly 65 million years after the non-bird dinosaurs died out. Small mammals did live alongside dinosaurs, and some of them survived the extinction.
Most scientists say the asteroid was the main cause and 'the final, killer blow'. Huge volcanic eruptions in India, the Deccan Traps, had been changing the climate for about two million years, which may have made things harder. Exactly which effects of the impact did the most damage is still debated.
No. Birds evolved from the same meat-eating dinosaur group as Tyrannosaurus rex, and their ancestors survived the extinction. So birds are living dinosaurs. There are at least 11,000 species of birds today.
Mostly small animals: early mammals, birds, turtles, crocodiles, lizards, snakes and frogs. No land animal heavier than about 25 kg survived. Many plants made it through too, because their seeds can wait out hard times.