Historical Geology 102
Life in the Mesozoic III


K-T Extinction

Required Reading - Dinosaur Extinction: The Volcano-Greenhouse Theory - Dewey M. McLean
Required Reading - Cretaceous Period: Life - University of California Museum of Paleontology
Required Reading - What Killed The Dinosaurs? The Great Mystery - University of California Museum of Paleontology
Required Reading - What Killed The Dinosaurs? Current Arguments - University of California Museum of Paleontology
Required Reading - What Killed The Dinosaurs? The Invalid Hypotheses - University of California Museum of Paleontology

Mesozoic Mass Extinction

Occurred at the end of the Mesozoic 66 m.y. ago
Stereotypically characterized as the extinction of the dinosaurs
Also included many other land and marine organisms
Dinosaurs were only one group of organisms affected by this mass extinction

Groups Affected by Mass Extinction

Ammonites, mosasaurs, plesiosaurs, pterosaurs and dinosaurs went completely extinct
Corals, clams, snails - experienced some extinctions of Families
Mammals, crocodiles, lizards, turtles, snakes, birds were some of the organisms that were unaffected or only slightly affected by this mass extinction

Mass Extinction

What caused the mass extinction of the dinosaurs?
What caused the mass extinction at the end of the Cretaceous?
Recent questions in extinction studies have asked, why do some organisms survive mass extinctions?

Patterns of Extinction

Gradual Extinction - a gradual decrease in the diversity of a group until it goes extinct
Sudden Extinction - a rapid or immediate termination of a group - "mass killing"
Which model applies best to the mass extinction at the end of the Mesozoic?

Impact Theory (Sudden Extinction)

Large asteroid or comet impacts 66 m.y. ago
Results in a cloud of dust thrown into atmosphere which reduced sunlight
Plants die first, then animals that eat plants starve, then carnivores starve
Evidence for this theory
- large impact basin in Yucatan Peninsula
- shocked quartz
- iridium-rich clay layer
Problems with this theory
Is an impact event sufficient to kill off both land and marine organism?
Why weren't all organisms affected equally?
Impact structure?
Enriched concentrations of iridium are found as the result of volcanic eruptions
Shocked quartz can also form as the result of volcanic eruptions or tectonic activity

Gradual Extinction

Fossil evidence argues that dinosaur populations were in decline
No impact is necessary to explain dinosaur extinction
Problems - only focuses on dinosaurs; what killed the other organisms?
Fossil record of dinosaurs is poor at best for studying population dynamics.

Eruption of Deccan Traps Flood Basalts

Huge volumes of lava erupted 70 to 65 m.y. ago in central India
Outgassing is believed to have caused changes in the chemistry of the ocean and atmosphere
This results in climate changes
Can climate changes occur faster than organisms can adapt?

Gamma-Ray Burst Theory

Extinction Survivors

Additional Readings in This Topic