End-cretaceous

Definition

The end-Cretaceous refers to the boundary marking the end of the Cretaceous period around 66 million years ago, known for one of the most significant mass extinctions in Earth's history. This event led to the extinction of approximately 75% of all species, including the non-avian dinosaurs, drastically altering the planet's biodiversity and ecological landscape. The end-Cretaceous is often linked to catastrophic events like asteroid impacts and volcanic activity that severely affected global climate conditions.

5 Must Know Facts For Your Next Test

1. The end-Cretaceous mass extinction is marked by significant geological evidence, including a distinct layer rich in iridium found globally, which supports the asteroid impact theory.
2. This extinction event led to the demise of numerous species, including all non-avian dinosaurs, paving the way for mammals to become the dominant terrestrial animals in subsequent periods.
3. Volcanic activity from the Deccan Traps in present-day India is also thought to have contributed to environmental changes during this time, further stressing ecosystems.
4. The end-Cretaceous event is one of five major mass extinctions in Earth's history and has been pivotal in shaping current biodiversity and ecological dynamics.
5. Fossil records indicate that after the end-Cretaceous extinction, there was a rapid diversification of mammals and birds as they adapted to new ecological niches.

Review Questions

• How did the end-Cretaceous event impact the evolutionary trajectory of mammals?
  • The end-Cretaceous event led to the extinction of many dominant species, particularly non-avian dinosaurs, which opened up ecological niches. With fewer competitors, mammals began to diversify and adapt to various environments. This allowed for the evolution of many new mammalian species that would eventually fill roles previously held by dinosaurs, thus changing the course of mammalian evolution significantly.
• Discuss the primary hypotheses regarding the causes of the end-Cretaceous mass extinction and their implications for biodiversity.
  • The primary hypotheses for the causes of the end-Cretaceous mass extinction include asteroid impact and extensive volcanic activity. The asteroid impact hypothesis is supported by evidence from the K-Pg boundary, with high iridium levels indicating an extraterrestrial source. The volcanic activity from the Deccan Traps likely caused climate change through massive eruptions leading to acid rain and global cooling. Both scenarios underscore how sudden environmental changes can dramatically reduce biodiversity, causing a shift in dominant species.
• Evaluate how understanding the end-Cretaceous extinction can inform current conservation efforts regarding biodiversity loss today.
  • Understanding the end-Cretaceous extinction provides crucial insights into how rapid environmental changes can lead to widespread biodiversity loss. By analyzing past events where ecosystems dramatically shifted, conservation efforts today can identify vulnerable species and habitats under threat from climate change or human activities. The lessons learned from this mass extinction highlight the importance of maintaining ecological balance and resilience in modern ecosystems to prevent similar large-scale losses in biodiversity.

Related terms

K-Pg boundary: The geological signature marking the transition between the Cretaceous and Paleogene periods, characterized by a layer of sediment that contains high levels of iridium, supporting the asteroid impact hypothesis.

mass extinction: A widespread and rapid decrease in biodiversity on Earth, where a significant number of species become extinct in a relatively short geological timeframe.

Chicxulub Crater: A large impact crater located on the Yucatán Peninsula in Mexico, believed to be the result of the asteroid impact that contributed to the end-Cretaceous mass extinction.