About 66 million years ago, a large asteroid struck Earth near what is now the Yucatán Peninsula in Mexico. The impact formed the Chicxulub crater and helped trigger one of the most famous mass extinctions in Earth history. Non-avian dinosaurs disappeared, along with many marine reptiles, flying reptiles, and other species.
This event matters because it shows how a sudden planetary disaster can reshape the history of life.
Key Facts
- The Chicxulub impact occurred about 66 million years ago at the end of the Cretaceous Period.
- The asteroid was likely about 10 km in diameter, roughly the size of a large city.
- Impact energy can be estimated by KE = 1/2 mv^2, where m is mass and v is speed.
- The Chicxulub crater is about 180 km wide and is buried partly beneath the Yucatán Peninsula and Gulf of Mexico.
- A global clay layer rich in iridium is key evidence for an extraterrestrial impact.
- Dust, sulfate aerosols, soot, wildfires, tsunamis, and climate disruption contributed to the extinction crisis.
Vocabulary
- Chicxulub crater
- The large buried impact crater near the Yucatán Peninsula linked to the end-Cretaceous mass extinction.
- Cretaceous Period
- The geologic period from about 145 million to 66 million years ago, ending with the extinction of non-avian dinosaurs.
- Iridium layer
- A thin global rock layer unusually rich in iridium that provides evidence of asteroid material spread around Earth.
- Mass extinction
- A short interval in geologic time when a large fraction of Earth's species die out worldwide.
- Ejecta
- Material blasted out of an impact crater and thrown into the air or across the surface.
Common Mistakes to Avoid
- Thinking the asteroid only killed dinosaurs by the blast wave. The local explosion was devastating, but global darkness, cooling, acid rain, food web collapse, and climate stress caused much of the worldwide extinction.
- Saying all dinosaurs went extinct. Birds are living dinosaurs, so the accurate statement is that non-avian dinosaurs went extinct.
- Confusing the asteroid impact with a slow climate change event only. Long-term environmental stress may have existed, but the Chicxulub impact was a sudden catastrophic event supported by crater and iridium evidence.
- Assuming fossils are found in one continuous layer showing every species dying at once. The fossil record is incomplete, so scientists combine fossil patterns with geochemical and crater evidence to reconstruct the event.
Practice Questions
- 1 An asteroid has a mass of 1.0 x 10^15 kg and strikes Earth at 20,000 m/s. Use KE = 1/2 mv^2 to calculate its kinetic energy in joules.
- 2 The Chicxulub crater is about 180 km wide, and the asteroid was about 10 km wide. How many times wider is the crater than the asteroid?
- 3 Explain why a layer of iridium found around the world is stronger evidence for an asteroid impact than a single fossil site with many dead animals.