Cretaceous

Definition

The Cretaceous is a geologic period that lasted from approximately 145 to 66 million years ago, marking the final segment of the Mesozoic Era. This period is characterized by significant evolutionary developments, particularly in terrestrial plants and marine life, as well as notable geological changes such as continental drift and climate variations that influenced ecosystems and species diversity.

5 Must Know Facts For Your Next Test

1. During the Cretaceous, angiosperms (flowering plants) began to dominate terrestrial ecosystems, leading to increased biodiversity and changes in pollination strategies.
2. The period saw major marine transgressions that created vast shallow seas, providing ideal conditions for the proliferation of marine life, including ammonites and marine reptiles.
3. The climate during the Cretaceous was generally warmer than today, with higher levels of CO2 leading to lush vegetation and diverse ecosystems both on land and in the oceans.
4. The Cretaceous ended with one of the most significant mass extinction events in Earth’s history, believed to be caused by an asteroid impact, leading to the extinction of approximately 75% of species including most dinosaurs.
5. Fossilized microfossils from the Cretaceous are crucial for understanding ancient marine environments and can indicate past climatic conditions and ecological shifts.

Review Questions

• How did the evolution of angiosperms during the Cretaceous impact terrestrial ecosystems?
  • The evolution of angiosperms during the Cretaceous had a profound impact on terrestrial ecosystems by introducing flowering plants that attracted a range of pollinators, which facilitated more complex interactions within food webs. This led to an increase in biodiversity as these plants adapted to various environments, allowing for new niches and habitats. Consequently, angiosperms became a dominant force in shaping plant communities and influencing animal life through food sources and habitat structures.
• Discuss the significance of marine transgressions during the Cretaceous and their effects on marine biodiversity.
  • Marine transgressions during the Cretaceous significantly altered coastlines and created expansive shallow seas, which provided rich habitats for marine organisms. These transgressions allowed for greater diversity of life forms, including an abundance of bivalves, ammonites, and marine reptiles that thrived in these environments. The increase in shallow marine areas enhanced nutrient availability and promoted complex ecosystems that supported diverse food webs, making this period crucial for understanding marine evolution.
• Evaluate the factors contributing to the mass extinction event at the end of the Cretaceous and its implications for life on Earth.
  • The mass extinction event at the end of the Cretaceous was primarily triggered by an asteroid impact that caused dramatic environmental changes, including wildfires, tsunamis, and a 'nuclear winter' effect from debris blocking sunlight. This led to a collapse of food chains both on land and in oceans, resulting in the extinction of about 75% of species, including most dinosaurs. The aftermath of this event allowed for new evolutionary pathways as mammals diversified in the absence of dinosaur dominance, reshaping life on Earth and paving the way for future ecosystems.

Related terms

Angiosperms:

A group of flowering plants that first appeared during the Cretaceous, marking a major evolutionary advancement in plant diversity.

Marine Transgression: The phenomenon during the Cretaceous when sea levels rose, leading to extensive shallow inland seas and significant impacts on marine ecosystems.

Dinosaurs: The dominant terrestrial vertebrates during the Cretaceous, which included a wide variety of species that thrived until their extinction at the end of this period.