SUBJECT GUIDE

Cretaceous Period

Tyler Rosen

Duration

Classification

Climate

Atmosphere

Organisms

References

Interesting Facts

Event And explanation

• Event: The Cretaceous–Paleogene (K–Pg) extinction event marks the end of the Cretaceous Period, which led to the extinction of the dinosaurs.
• Explanation: This mass extinction event, which occurred around 66 million years ago, is believed to have been caused by a combination of volcanic activity, climate change, and a massive asteroid impact in the Yucatan Peninsula (Chicxulub Crater). The impact caused global wildfires, a "nuclear winter" effect that blocked sunlight, and subsequent disruptions to the food chain.

Events and explanation

References

Cope, E. D. (Edward Drinker) et al. Review of the Vertebrata of the Cretaceous Period Found West of the Mississippi River. Washington, D.C: U.S. Geological Survey, 1874. Print.

Mudge, B. F. (Benjamin Franklin). Notes on the Tertiary and Cretaceous Periods of Kansas. Washington: s.n., 1876. Print.

Atmosphere

The atmosphere had higher levels of carbon dioxide, contributing to the warm climate.

The Cretaceous Period lasted for approximately 79 million years, from about 145 million years ago to 66 million years ago.

Duration

Climate

The world during the Cretaceous Period was generally warmer than today, with no polar ice caps. Sea levels were much higher due to warmer global temperatures, which caused extensive inland seas.

• Birds: Many scientists believe that birds are the descendants of small theropod dinosaurs, which means birds survived the extinction event that killed their dinosaur relatives.
• Flowering Plants: The Cretaceous Period saw the first appearance of flowering plants, which led to changes in ecosystems and the types of herbivores that thrived.
• Sea Levels: The sea level during the Cretaceous Period was at its highest in Earth’s history, covering much of what is now North America with shallow seas.
• Continents: During this period, the supercontinent Pangaea continued to break apart, and the Atlantic Ocean widened as the Americas drifted farther from Europe and Africa.
• Marine Life: Large marine reptiles like Mosasaurus and Plesiosaurs ruled the oceans, while ammonites (related to modern squid) were widespread.
• Insects: Some of the first pollinating insects appeared, helping flowering plants spread.

Interesting facts

Organisms

This period was famous for its diverse range of dinosaurs, such as the Tyrannosaurus rex and Triceratops. Flowering plants (angiosperms) also started to evolve during this time, and marine life included large reptiles like Mosasaurus.

Classification

It is part of the Mesozoic Era and follows the Jurassic Period, marking the final period of the Mesozoic.