Cretaceous-Paleogene boundary

Definition

The Cretaceous-Paleogene boundary marks a significant geological event that occurred approximately 66 million years ago, signifying the transition from the Cretaceous period to the Paleogene period. This boundary is best known for the mass extinction event that led to the demise of around 75% of Earth's species, including non-avian dinosaurs, and it fundamentally altered terrestrial ecosystems and evolutionary trajectories of vertebrates and invertebrates.

5 Must Know Facts For Your Next Test

1. The Cretaceous-Paleogene boundary is characterized by a distinct layer of clay rich in iridium, which supports the hypothesis of an asteroid impact as a primary cause of the mass extinction.
2. Fossil evidence shows a dramatic decline in diversity and abundance of both vertebrates and invertebrates at this boundary, highlighting its role as a critical point in Earth's history.
3. This extinction event paved the way for mammals to become the dominant terrestrial vertebrates, leading to significant evolutionary changes during the Paleogene period.
4. The event is also associated with extensive volcanic activity in the Deccan Traps region of India, which may have contributed to environmental changes affecting global climate.
5. After the Cretaceous-Paleogene boundary, many new species emerged, filling ecological niches left vacant by extinct groups, demonstrating how life can rebound after catastrophic events.

Review Questions

• How did the Cretaceous-Paleogene boundary affect the diversity of terrestrial vertebrate and invertebrate populations?
  • The Cretaceous-Paleogene boundary led to a dramatic reduction in diversity among both terrestrial vertebrates and invertebrates. This mass extinction resulted in the loss of approximately 75% of species, including all non-avian dinosaurs. The ecological niches that became vacant after this event allowed for new groups of organisms to evolve and diversify, setting the stage for mammalian dominance in subsequent periods.
• Discuss the implications of the Chicxulub Crater in relation to the events surrounding the Cretaceous-Paleogene boundary.
  • The Chicxulub Crater serves as a crucial piece of evidence linking an asteroid impact to the mass extinction at the Cretaceous-Paleogene boundary. This impact is believed to have caused widespread environmental disruption, including fires, tsunamis, and a 'nuclear winter' effect from debris blocking sunlight. The rapid changes in climate and habitat conditions contributed significantly to the extinction of many species and altered ecological dynamics across terrestrial systems.
• Evaluate the long-term effects of the Cretaceous-Paleogene boundary on evolutionary trajectories within terrestrial ecosystems.
  • The Cretaceous-Paleogene boundary had profound long-term effects on evolution within terrestrial ecosystems. The mass extinction opened up ecological opportunities for mammals and other surviving groups to diversify and adapt into various niches previously occupied by dominant species. This event catalyzed significant evolutionary change, leading to the emergence of mammals as dominant land animals and influencing patterns of biodiversity that shaped future ecosystems throughout the Paleogene and beyond.

Related terms

Mass Extinction: A rapid and widespread decrease in biodiversity on Earth, characterized by the extinction of a large number of species in a relatively short geological timeframe.

Chicxulub Crater: A large impact crater located on the Yucatán Peninsula in Mexico, believed to be the site of the asteroid impact that triggered the mass extinction at the Cretaceous-Paleogene boundary.

Paleontology: The scientific study of the history of life on Earth through the examination of plant and animal fossils.