End-Cretaceous extinction

Definition

The End-Cretaceous extinction, also known as the Cretaceous-Paleogene (K-Pg) extinction event, refers to a major mass extinction that occurred approximately 66 million years ago, resulting in the disappearance of about 75% of Earth's species, including the non-avian dinosaurs. This event marked the boundary between the Cretaceous and Paleogene periods and is often linked to catastrophic events such as asteroid impacts and volcanic activity that drastically altered Earth's environment.

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 and led to the loss of approximately 75% of all species, including most dinosaurs.
2. The leading theories for its cause include a combination of an asteroid impact and extensive volcanic eruptions that caused drastic climate changes.
3. The impact hypothesis is supported by evidence of iridium-rich clay layers found globally, indicating an extraterrestrial object struck Earth.
4. The extinction paved the way for mammals to become the dominant terrestrial vertebrates, leading to the eventual rise of mammals into diverse forms, including humans.
5. Paleontological evidence shows a gradual decline in dinosaur diversity prior to the extinction event, suggesting multiple stress factors at play even before the mass extinction occurred.

Review Questions

• What were the main hypotheses proposed to explain the causes of the End-Cretaceous extinction, and how do they interrelate?
  • The two main hypotheses for the End-Cretaceous extinction are the asteroid impact theory and volcanic activity associated with the Deccan Traps. The asteroid impact is believed to have caused immediate and drastic changes in climate and ecosystems due to dust and debris blocking sunlight. Concurrently, volcanic eruptions released large amounts of greenhouse gases and toxins into the atmosphere, contributing to long-term climate change. Together, these factors created an inhospitable environment for many species, leading to widespread extinctions.
• Discuss how the End-Cretaceous extinction influenced the evolutionary trajectory of life on Earth after its occurrence.
  • Following the End-Cretaceous extinction, there was a significant shift in Earth's ecosystems. With dinosaurs gone, mammals began to diversify and occupy ecological niches previously dominated by dinosaurs. This adaptive radiation led to the emergence of new mammalian forms and eventually paved the way for primates and human ancestors. The extinction event fundamentally reshaped biodiversity on Earth, setting a new evolutionary course that would result in modern ecosystems.
• Evaluate the long-term ecological impacts of the End-Cretaceous extinction event on terrestrial and marine life during subsequent geological periods.
  • The End-Cretaceous extinction had profound long-term ecological impacts that shaped both terrestrial and marine environments. In terrestrial ecosystems, it facilitated mammalian diversification and dominance while altering plant communities as seed ferns and certain gymnosperms declined. In marine environments, coral reefs struggled initially but eventually rebounded with new species. The extinction also opened up niches for new types of organisms like birds from theropod ancestors. These shifts significantly influenced community structures and evolutionary pathways in both realms for millions of years following this pivotal event.

Related terms

Chicxulub Crater: A massive impact crater located on the Yucatán Peninsula in Mexico, believed to be the site of an asteroid impact that contributed to the End-Cretaceous extinction.

Deccan Traps: A large volcanic province in India, consisting of extensive basaltic lava flows, which played a significant role in climate changes during the late Cretaceous period, contributing to the extinction event.

Mass Extinction: A rapid and widespread decrease in the biodiversity on Earth, typically characterized by the loss of a large number of species across various taxa within a relatively short geological time frame.