End-cretaceous

Definition

The end-cretaceous refers to the boundary between the Cretaceous and Paleogene periods, approximately 66 million years ago, marked by a significant mass extinction event that led to the disappearance of about 75% of Earth's species, including the dinosaurs. This event reshaped ecological communities and altered evolutionary pathways, highlighting how drastic environmental changes can impact biodiversity and community structure over geological time scales.

5 Must Know Facts For Your Next Test

1. The end-cretaceous mass extinction is one of the five major extinction events in Earth's history, significantly altering the course of evolution.
2. The K-Pg boundary is identified by a layer of sediment rich in iridium, suggesting extraterrestrial impact, likely from an asteroid or comet.
3. The extinction led to the decline of dominant groups like dinosaurs and marine reptiles, paving the way for mammals to become more diverse and dominant in subsequent periods.
4. Volcanic activity during this time also contributed to environmental changes, including climate shifts due to increased atmospheric carbon dioxide.
5. Ecological recovery after the end-cretaceous event took millions of years, demonstrating how ecosystems can be resilient yet slow to rebound from such large-scale disruptions.

Review Questions

• How did the end-cretaceous mass extinction influence the structure and diversity of ecological communities during the subsequent Paleogene period?
  • The end-cretaceous mass extinction drastically reshaped ecological communities by removing dominant species such as dinosaurs and many marine reptiles. This allowed for new groups like mammals and birds to diversify and fill ecological niches left vacant by extinct species. The extinction opened up opportunities for evolutionary experimentation, leading to an increase in biodiversity and new community structures during the Paleogene period.
• Discuss the evidence supporting the asteroid impact hypothesis related to the end-cretaceous event and its implications for ecological stability.
  • The asteroid impact hypothesis is supported by geological evidence found at the K-Pg boundary, which includes a layer rich in iridium, a metal more common in asteroids than on Earth. This event likely triggered catastrophic environmental changes such as wildfires, tsunamis, and a 'nuclear winter' effect that blocked sunlight, disrupting photosynthesis. These dramatic shifts in conditions led to widespread habitat loss and species extinction, emphasizing how external forces can destabilize established ecological communities.
• Evaluate the long-term ecological consequences of the end-cretaceous extinction event on biodiversity trends throughout Earth's history.
  • The long-term ecological consequences of the end-cretaceous extinction event have had profound impacts on biodiversity trends throughout Earth's history. The removal of dominant species allowed for mammalian diversification and the eventual rise of humans. The patterns observed after this extinction highlight resilience in ecosystems but also underline vulnerabilities when facing rapid environmental changes. This event serves as a reminder of how significant shifts can alter evolutionary trajectories and influence future biodiversity dynamics.

Related terms

Mass Extinction: A rapid and widespread decrease in biodiversity on Earth, characterized by the loss of many species in a relatively short geological time frame.

K-Pg Boundary:

The geological signature that marks the end of the Cretaceous period and the beginning of the Paleogene period, recognized by a distinct layer of clay enriched with iridium.

Asteroid Impact: A hypothesis suggesting that a massive asteroid collision with Earth contributed significantly to the environmental changes causing the end-cretaceous extinction event.