Cretaceous-Paleogene Extinction Event

Definition

The Cretaceous-Paleogene extinction event was a major biological mass extinction that occurred approximately 66 million years ago, marking the end of the Cretaceous period and the transition to the Paleogene period. This event is most famous for causing the extinction of about 75% of all species on Earth, including all non-avian dinosaurs, fundamentally reshaping the planet's biodiversity and ecological systems.

5 Must Know Facts For Your Next Test

1. The Cretaceous-Paleogene extinction event is primarily attributed to a combination of an asteroid impact and extensive volcanic activity, particularly from the Deccan Traps in present-day India.
2. The event led to the complete extinction of all non-avian dinosaurs, which had been dominant terrestrial vertebrates for millions of years.
3. Birds are considered the only surviving lineage of dinosaurs, evolving from theropod ancestors during the late Cretaceous period before the extinction event.
4. The loss of biodiversity following this extinction opened up ecological niches, allowing mammals to diversify and eventually become the dominant terrestrial animals in the subsequent Paleogene period.
5. Evidence from fossil records indicates that while many species went extinct, some groups of reptiles, amphibians, and plants survived and adapted to the new environmental conditions.

Review Questions

• What were some of the primary causes identified for the Cretaceous-Paleogene extinction event, and how did they contribute to such widespread extinctions?
  • The primary causes identified for the Cretaceous-Paleogene extinction event include a massive asteroid impact and extensive volcanic eruptions. The asteroid impact created the Chicxulub Crater, leading to immediate environmental changes like wildfires, tsunamis, and a 'nuclear winter' effect due to debris blocking sunlight. Meanwhile, volcanic activity from the Deccan Traps released gases that altered climate patterns. Together, these factors disrupted ecosystems and food chains, contributing to the rapid extinction of about 75% of all species.
• Discuss the significance of the Iridium layer found in geological records related to the Cretaceous-Paleogene extinction event.
  • The Iridium layer found in geological records serves as crucial evidence supporting the asteroid impact hypothesis for the Cretaceous-Paleogene extinction event. Iridium is rare on Earth's surface but common in asteroids, suggesting a significant extraterrestrial impact. The global distribution of this layer corresponds with the timing of the mass extinction, further solidifying its role as a marker for this pivotal moment in Earth's history. This layer allows scientists to correlate geological and biological changes during this period.
• Evaluate how the Cretaceous-Paleogene extinction event reshaped Earth's biodiversity and set the stage for mammalian dominance in subsequent eras.
  • The Cretaceous-Paleogene extinction event drastically reshaped Earth's biodiversity by eliminating dominant groups such as non-avian dinosaurs and many marine reptiles. This mass extinction created vacant ecological niches that allowed surviving species to adapt and diversify rapidly. In particular, mammals, which had previously been small and relatively inconspicuous, began to evolve into various forms that occupied new roles within ecosystems. This shift not only paved the way for mammals to become dominant terrestrial vertebrates but also significantly influenced evolutionary trajectories in flora and fauna throughout the Paleogene period and beyond.

Related terms

Chicxulub Crater: A large crater located in Mexico's Yucatan Peninsula, believed to be the impact site of a giant asteroid that contributed to the Cretaceous-Paleogene extinction event.

Iridium Layer: A distinct layer of sediment found globally in the geological record, rich in iridium, which supports the asteroid impact hypothesis for the extinction event.

Mass Extinction: A widespread and rapid decrease in biodiversity on Earth, marked by the extinction of a significant number of species in a relatively short geological time frame.