Lecture 3: Chapter 25 - Mass Extinctions and Adaptive Radiation

Introduction

• Continuation from past lectures on the origin of life and eukaryotic formation
• Focus on mass extinctions and their impact on life
• Future class discussion will cover changes in body plans

Fossil Record and Mass Extinctions

• Fossil records show significant events leading to mass extinctions
• Rapid Environmental Changes: Disruptive changes causing extinction of many species
• Extinction Rate: Represented by a blue line with peaks indicating mass extinction events
• Taxonomic Families: Red line shows growth over time despite extinctions
• Mass extinctions reset life allowing for evolutionary processes

Significant Mass Extinctions

Permian Mass Extinction ("Great Dying")

• Claimed 96% of marine species and significant insect orders
• Caused by volcanic eruptions in Siberia
• Resulted in drastic atmospheric and water chemistry changes

Cretaceous Mass Extinction

• Led to the extinction of large dinosaurs
• Caused by an asteroid impact in the Yucatan Peninsula (Chicxulub crater)
• Cleared the path for the rise of mammals

Adaptive Radiation Post Mass Extinction

• Definition: Evolution of organisms surviving mass extinction to occupy available niches
• Speciation processes lead to diversification and filling ecological roles
• Example: Birds spreading seeds leading to plant radiation

Case Study: Hawaii as an Example of Adaptive Radiation

• Hawaiian islands showcase adaptive radiation due to their recent formation
• Islands allow for unique evolution due to isolation
• Founding populations (like seeds dropped by birds) rapidly evolve

Conclusion

• Mass extinctions are common in Earth's history
• Adaptive radiation follows, enabling new species to thrive
• Upcoming class will resume in-person lectures
• Encouragement to explore adaptive radiation further, such as visiting Maui volcano