The K-Pg extinction event
Describe the Cretaceous–Palaeogene (K-Pg) extinction event approximately 66 million years ago, including the asteroid impact theory and its evidence (iridium layer, Chicxulub crater), and understand that this ended the reign of non-avian dinosaurs
What a learner can do afterwards
- State that the K-Pg extinction happened about 66 million years ago and wiped out non-avian dinosaurs
- Describe the asteroid impact hypothesis and name the Chicxulub crater in Mexico
- Explain one piece of evidence: the iridium-rich layer found worldwide in rocks from that time
1 · Read
About 66 million years ago, at the end of the Cretaceous period, all non-avian dinosaurs died out. Non-avian means not birds. Some birds survived, and birds are dinosaurs alive today. This was part of the K-Pg mass extinction, when many kinds of plants and animals died out. K-Pg names the boundary between the Cretaceous and the following Palaeogene period.
A huge asteroid, a rock from space, struck Earth near what is now Mexico's Yucatan Peninsula. The impact formed Chicxulub crater, which is mostly buried beneath land and sea. The crater and rocks from that time provide evidence that the impact was a major cause of the K-Pg extinction.
A thin layer in rocks from the time of the extinction is rich in iridium. Scientists have found this layer in many parts of the world. Iridium is rare in Earth's crust, but many asteroids contain much more of it. The layer's age and wide spread, together with Chicxulub crater, support an asteroid impact.
The asteroid impact formed a crater and sent dust and soot into the air. Less sunlight meant less plant growth. Plant eaters then had less food, and animals that ate them were affected too. These changes affected places far from the crater over time. Some birds survived, even though all non-avian dinosaurs died out.
A giant asteroid struck Earth about 66 million years ago, and the worldwide iridium layer in rocks is key evidence for that impact.
Lesson, questions and flashcards written for this dataset.
Readings written for this dataset. The linked videos 'Did an asteroid kill the dinosaurs?' and 'How did all dinosaurs except birds go extinct?' are by the American Museum of Natural History and were cataloged through Khan Academy. The AMNH rights notice for 'Did an asteroid kill the dinosaurs?' specifies personal educational use. The third linked video is by TED-Ed with Sean P. S. Gulick. Usage terms for the second and third videos remain unverified.
More to read
Testing an extinction explanation
Scientists compare an explanation with evidence from the past. Chicxulub crater records a large impact. A widespread iridium-rich rock layer dates to the time of the K-Pg extinction. Together, these finds support an impact as a major cause.
Scientists also investigate whether volcanic activity and other environmental changes added stress. Studying those contributions does not remove the impact evidence. An explanation must also account for survivors, including some birds.
How the impact affected food
The impact changed conditions far beyond the crater. Dust and soot in the air reduced sunlight. Many plants then grew less or died. Animals that ate plants had less food. Animals that ate those plant eaters were affected too.
This chain helps explain why an impact could harm animals far from where it landed. It does not mean every animal was hit by the asteroid or every plant died. Some birds survived the changes.
Extinction does not mean all life ends
A species is a kind of living thing. During a mass extinction, many species die out around the world. The K-Pg extinction affected many groups of plants and animals about 66 million years ago.
All non-avian dinosaurs died out. Non-avian means not birds. It does not mean unable to fly. Some birds survived, and birds are dinosaurs. The extinction ended some groups while leaving survivors from others.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.