Cretaceous

Cretaceous is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, following the Jurassic and preceding the Paleogene. The Cretaceous was a time of significant geological, climatic, and biological change, including the extinction of the dinosaurs.

Geology

The Cretaceous is defined by the deposition of chalk (a type of limestone), which is abundant in the sedimentary rock record of the period. The name "Cretaceous" is derived from the Latin "creta", meaning chalk. The period is divided into two epochs: the Early Cretaceous (145 to 100.5 Mya) and the Late Cretaceous (100.5 to 66 Mya).

Climate

The climate during the Cretaceous was warmer than today, with high eustatic sea levels and a lack of polar ice caps. This resulted in extensive shallow seas and marine transgressions in many parts of the world. The warm climate was likely due to high levels of carbon dioxide in the atmosphere.

Biology

The Cretaceous saw the evolution and diversification of many new groups of organisms. Dinosaurs continued to be the dominant terrestrial vertebrates, but the period also saw the first appearance of many modern groups of organisms, including birds, mammals, and flowering plants.

Extinction

The end of the Cretaceous is marked by one of the most significant mass extinctions in Earth's history, known as the Cretaceous-Paleogene extinction event. This event, which occurred approximately 66 Mya, resulted in the extinction of all dinosaur groups except for the birds.

See also

• Geologic time scale
• Mesozoic
• Jurassic
• Paleogene

References

Cretaceous Resources
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