End-cretaceous mass extinction

Definition

The end-cretaceous mass extinction was a significant event that occurred approximately 66 million years ago, leading to the extinction of about 75% of all species on Earth, including the non-avian dinosaurs. This event marks the boundary between the Cretaceous and Paleogene periods in the geologic time scale, highlighting a pivotal moment in Earth's history that dramatically reshaped the planet's biodiversity and ecosystems.

5 Must Know Facts For Your Next Test

1. The end-cretaceous mass extinction is primarily attributed to a combination of catastrophic events, including an asteroid impact and volcanic activity, which led to drastic climate changes.
2. Evidence for the asteroid impact is found in the iridium-rich layer at the K-T boundary, supporting the hypothesis that an extraterrestrial object caused widespread destruction.
3. This extinction event resulted in the disappearance of many species, including all non-avian dinosaurs, paving the way for mammals to become the dominant terrestrial vertebrates.
4. The global climate was severely affected by this event, leading to 'nuclear winter' conditions that drastically reduced sunlight and disrupted photosynthesis.
5. The aftermath of the end-cretaceous mass extinction allowed for a rapid evolutionary radiation of surviving species, contributing to the formation of modern ecosystems.

Review Questions

• What evidence supports the hypothesis that an asteroid impact was responsible for the end-cretaceous mass extinction?
  • The primary evidence supporting the asteroid impact hypothesis is found in the K-T boundary layer, which contains high levels of iridium, a metal rare on Earth but common in asteroids. The Chicxulub Crater in Mexico aligns with this timing and provides geological evidence of a massive impact. Additionally, studies of sedimentary rock layers show significant disturbances consistent with global upheaval, indicating that this event led to drastic environmental changes that contributed to widespread extinctions.
• Discuss how volcanic activity during this period may have contributed to environmental changes that facilitated the end-cretaceous mass extinction.
  • Volcanic activity, particularly from the Deccan Traps in present-day India, released vast amounts of ash and gases into the atmosphere. This led to significant climate alterations, such as global cooling and acid rain, which adversely affected plant life and disrupted ecosystems. The combined effects of volcanic eruptions and the asteroid impact created extreme conditions that were unsustainable for many species, accelerating their decline and eventual extinction.
• Evaluate the long-term ecological impacts of the end-cretaceous mass extinction on subsequent evolutionary patterns in mammals and birds.
  • The end-cretaceous mass extinction set off a cascade of ecological transformations that paved the way for mammals and birds to flourish. With non-avian dinosaurs gone, mammals diversified rapidly into various niches previously occupied by dinosaurs. This led to an explosion of mammalian forms during the Paleogene Period, including the ancestors of modern mammals. Similarly, birds adapted and evolved into new forms as they filled ecological gaps left by extinct species, demonstrating how this mass extinction fundamentally reshaped life's evolutionary trajectory on Earth.

Related terms

Chicxulub Crater: A large impact crater located in the Yucatán Peninsula, believed to be the site of the asteroid impact that triggered the end-cretaceous mass extinction.

Paleogene Period: The geological period that followed the Cretaceous, beginning about 66 million years ago, marked by the diversification of mammals and birds after the mass extinction.

K-T Boundary: The geological signature of the end-cretaceous mass extinction, characterized by a layer of iridium-rich clay that signifies the impact event and biological turnover.