At the end of the Cretaceous Period about 66 million years ago, nonavian dinosaurs and many other species disappeared in a mass extinction. Luis Alvarez, a Nobel Prize winning physicist, and his son Walter Alvarez, a geologist, helped show that this event was linked to a giant asteroid impact. Their work connected physics, chemistry, geology, and paleontology into one evidence based explanation.
It also showed how a single event can rapidly change Earth’s climate and life systems.
Key Facts
- The K-Pg extinction occurred about 66 million years ago and eliminated nonavian dinosaurs.
- The Alvarez team found unusually high iridium levels in a thin clay layer at the K-Pg boundary.
- Iridium is rare in Earth’s crust but more common in many asteroids and meteorites.
- Impact energy can be estimated with KE = 1/2 mv^2.
- The Chicxulub crater near the Yucatán Peninsula is about 180 km in diameter.
- Dust, aerosols, and soot from the impact likely reduced sunlight, cooled the surface, and disrupted food chains.
Vocabulary
- K-Pg boundary
- The rock layer marking the transition between the Cretaceous Period and the Paleogene Period about 66 million years ago.
- Iridium anomaly
- An unusually high concentration of iridium in a rock layer, used as evidence for material from an asteroid impact.
- Chicxulub crater
- The buried impact crater near the Yucatán Peninsula that is linked to the asteroid impact at the K-Pg boundary.
- Ejecta
- Rock, dust, and molten material thrown outward from an impact or volcanic eruption.
- Mass extinction
- A relatively short interval in Earth history when a large fraction of species die out worldwide.
Common Mistakes to Avoid
- Assuming the asteroid killed every dinosaur instantly is wrong because the impact caused both immediate destruction and longer term climate effects that disrupted ecosystems.
- Treating iridium as proof by itself is wrong because scientists also rely on shocked minerals, glassy spherules, crater evidence, and fossil patterns.
- Confusing the K-Pg boundary with the end of all dinosaurs is wrong because birds are living descendants of theropod dinosaurs.
- Thinking paleontology only studies fossils is wrong because extinction research also uses geochemistry, geophysics, sedimentology, and climate evidence.
Practice Questions
- 1 An asteroid has a mass of 1.0 x 10^15 kg and strikes Earth at 2.0 x 10^4 m/s. Use KE = 1/2 mv^2 to calculate its kinetic energy.
- 2 A clay sample from the K-Pg boundary contains 6.0 parts per billion of iridium, while nearby ordinary sediment contains 0.3 parts per billion. How many times higher is the iridium concentration in the boundary layer?
- 3 Explain why a thin global layer rich in iridium, combined with a large impact crater of the same age, is stronger evidence than either observation alone.