Cretaceous-Paleogene boundary

Definition

The Cretaceous-Paleogene boundary marks a significant geological and biological transition approximately 66 million years ago, characterized by a mass extinction event that led to the demise of around 75% of Earth's species, including the non-avian dinosaurs. This boundary is crucial for understanding the fossil record and transitional forms, as it highlights shifts in biodiversity and the emergence of new life forms following a major ecological upheaval.

5 Must Know Facts For Your Next Test

1. The Cretaceous-Paleogene boundary is often associated with the impact of a large asteroid or comet near present-day Yucatán Peninsula, which is believed to have caused widespread fires, tsunamis, and a 'nuclear winter' effect.
2. This boundary not only signifies the end of the dinosaurs but also marks the beginning of the Cenozoic Era, known as the 'Age of Mammals', where mammals began to diversify and dominate terrestrial ecosystems.
3. Fossils found in sediment layers above the Cretaceous-Paleogene boundary show a dramatic shift in species composition, indicating a rapid recovery and radiation of new life forms after the extinction event.
4. The iridium layer found at the Cretaceous-Paleogene boundary is a key piece of evidence supporting the asteroid impact hypothesis, as iridium is rare on Earth but common in asteroids.
5. Study of this boundary has provided paleontologists with essential insights into patterns of evolution, adaptation, and extinction, illustrating how life on Earth can rebound following catastrophic events.

Review Questions

• How did the Cretaceous-Paleogene boundary influence our understanding of mass extinctions in Earth's history?
  • The Cretaceous-Paleogene boundary serves as a pivotal case study for mass extinctions, illustrating how rapid environmental changes can lead to widespread species loss. By analyzing this event, scientists have gained insight into the causes and consequences of mass extinctions, including how they can reshape ecosystems. This understanding helps us recognize patterns in biodiversity loss and recovery in both past and present contexts.
• Discuss the role of transitional forms found in the fossil record around the Cretaceous-Paleogene boundary in understanding evolutionary processes.
  • Transitional forms found near the Cretaceous-Paleogene boundary are essential for illustrating evolutionary changes that occurred after the mass extinction. These fossils showcase characteristics that bridge gaps between extinct species and their living relatives, helping scientists trace lineage and understand how new groups emerged. Such findings highlight evolutionary adaptability and the mechanisms driving speciation following significant environmental shifts.
• Evaluate the long-term impacts of the Cretaceous-Paleogene boundary on mammalian evolution and global biodiversity.
  • The Cretaceous-Paleogene boundary had profound long-term impacts on mammalian evolution by clearing ecological niches that allowed mammals to diversify extensively in the absence of dinosaurs. Following this event, mammals underwent adaptive radiations, leading to the emergence of various forms that would dominate later epochs. This shift not only reshaped terrestrial ecosystems but also influenced global biodiversity patterns, underscoring how catastrophic events can act as catalysts for significant evolutionary developments.

Related terms

Mass extinction: A rapid and widespread decrease in biodiversity on Earth, where a significant number of species go extinct in a relatively short period, often linked to environmental changes or catastrophic events.

Fossil record: The collection of all known fossils and their placement in chronological order, providing evidence for the history of life on Earth and the evolution of species over time.

Transitional forms: Fossils that exhibit traits common to both an ancestral group and its derived descendant group, providing insight into the evolutionary process and demonstrating how species have changed over time.