End-cretaceous extinction

Definition

The end-cretaceous extinction refers to a mass extinction event that occurred approximately 66 million years ago, marking the boundary between the Cretaceous and Paleogene periods. This event is most famous for the dramatic decline of the dinosaurs, alongside a significant loss of marine and terrestrial species, believed to have been triggered by a combination of volcanic activity, climate change, and a massive asteroid impact in present-day Mexico.

5 Must Know Facts For Your Next Test

1. The end-cretaceous extinction is one of the five major mass extinctions in Earth's history, resulting in the extinction of about 75% of all species.
2. The asteroid impact at Chicxulub is widely considered the primary driver of this extinction event due to the immediate and catastrophic environmental changes it caused.
3. In addition to the asteroid impact, extensive volcanic activity from the Deccan Traps released vast amounts of gases that altered the climate and contributed to the extinction.
4. This event led to the rise of mammals, as many ecological niches previously occupied by dinosaurs became available for other species to thrive.
5. Evidence of this extinction includes a distinct layer of iridium-rich clay found in the geological record, marking the boundary between the Cretaceous and Paleogene periods.

Review Questions

• What evidence supports the theory that an asteroid impact was a significant cause of the end-cretaceous extinction?
  • The most compelling evidence for the asteroid impact theory comes from the discovery of the Chicxulub Crater, which is linked to a layer of iridium-rich clay found globally at the Cretaceous-Paleogene boundary. This iridium anomaly suggests a cosmic impact since iridium is rare on Earth's surface but common in asteroids. The timing of this layer coincides with a dramatic decrease in biodiversity, further supporting that this event played a crucial role in triggering the mass extinction.
• Discuss how volcanic activity may have influenced environmental conditions during the end-cretaceous extinction.
  • Volcanic activity from the Deccan Traps is believed to have significantly influenced environmental conditions during the end-cretaceous extinction by releasing vast amounts of sulfur dioxide and carbon dioxide into the atmosphere. These gases would have led to acid rain and contributed to global cooling initially, followed by long-term warming due to greenhouse gas emissions. Such drastic changes in climate would have disrupted ecosystems and contributed to species extinctions alongside the effects of the asteroid impact.
• Evaluate how the end-cretaceous extinction reshaped Earth's biodiversity and ecological landscape following this event.
  • The end-cretaceous extinction fundamentally reshaped Earth's biodiversity by eliminating dominant groups like dinosaurs, allowing mammals and other organisms to fill ecological niches left vacant. In the aftermath, mammalian diversity increased rapidly, leading to the eventual rise of large mammals and birds. The extinction paved the way for new evolutionary pathways and adaptations among surviving species, ultimately resulting in an ecological landscape that was markedly different from that of the late Cretaceous period.

Related terms

Chicxulub Crater: A large impact crater located on the Yucatán Peninsula in Mexico, formed by the asteroid impact associated with the end-cretaceous extinction.

Deccan Traps: A large volcanic province in India, characterized by extensive basalt lava flows, which contributed to environmental changes during the end-cretaceous period.

Mass extinction: A significant and rapid reduction in biodiversity on Earth, characterized by the widespread loss of species across multiple taxonomic groups.