Lecture Notes: Cretaceous-Paleogene (K-Pg) Extinction

Introduction

• Key Focus: Explore hypotheses for the cause of the K-Pg extinction.
• Two Main Hypotheses:
  • Bolide impact
  • Major volcanic event

Impact of the Extinction

• Affected both marine and terrestrial life.
• Non-avian dinosaurs and marine organisms like shelled cephalopods were major groups that went extinct.
• Not the largest extinction event historically; the end-Permian extinction was more devastating.

The Bolide Impact Hypothesis

• Location: Yucatan Peninsula
• Evidence:
  • High iridium concentration in a global clay layer.
  • Shocked quartz and impact spherules.
  • Discovery of the Chicxulub crater in the 1990s supports the impact hypothesis.
• Impact Details:
  • Bolide approximately 10 km in diameter.
  • Impact debris pattern consistent with a central impact site.

The Volcanic Hypothesis

• Location: Deccan Traps
• Evidence:
  • Extensive basalt deposits dating from 65.5 to 66.5 million years ago.
  • Potential for prolonged environmental disruption.
• Challenges:
  • Timing overlaps with bolide impact, complicating the extinction story.

Mechanisms of Extinction

• Bolide Impact:
  • Immediate fires and heat stress.
  • Impact winter due to solar radiation blockage.
  • Collapse of primary productivity leading to starvation.
• Volcanism:
  • Long-term ocean acidification.
  • Global warming due to carbon dioxide release.
  • Oxygen stress in oceans.

Selectivity of Extinction

• Winners:
  • Omnivores and detritus feeders.
  • Birds with seed-adapted beaks.
  • Fungi and spore-producing plants.
• Losers:
  • Large-bodied animals.
  • Specialized diet animals and oceanic plankton.
• Implications:
  • Selectivity points to a collapse in food availability and productivity.

Post-Impact Consequences

• Starvation and Cooling:
  • Decreased sunlight led to reduced photosynthesis and abrupt cooling.
• Geochemical Evidence:
  • Carbon isotope analysis indicated a collapse in marine productivity.

Other Considerations

• Location of Impact:
  • Unique because of hydrocarbon and sulfate-rich site, enhancing the extinction impact.
• Further Studies:
  • Continuous examination of evidence and alternative hypotheses necessary.

Conclusion

• Current Consensus:
  • Strong evidence supports the bolide impact as the extinction trigger.
  • Recovery from the extinction was rapid, leading to new ecological roles and ecosystems.

Next Steps

• Future Focus:
  • Exploring the recovery and evolution of ecosystems post-extinction.