A Brief Overview of the Cretaceous Period for Middle School Science Classes

Dec 15, 2024

3 min read

Earth history is a fascinating topic! It is also a massive topic! The reading passage below will teach you all about the Cretaceous Period. If you want to learn more (and why wouldn't you?!), you can check out my Earth History page. I also have all of my passages available at Teachers Pay Teachers. They come with so many extras to get your students thinking about the content! I also recommend scrolling to the bottom of the page to check out my digital picture book on the Cretaceous Period!

Cretaceous Period Reading Passage for Middle School Science

Triassic-Jurassic Extinction Event

The Jurassic period ended with a minor mass extinction, but most life was unaffected. Dinosaurs continued to roam the land, fish continued to swim in the sea, and pterosaurs continued to fly through the skies.

Continents

Throughout the Cretaceous, continents continued to separate. By the end of the period, the continents were in mostly the same positions as today except India hadn’t joined Asia and Australia and Antarctica were still connected.

Angiosperms

The warm climate allowed plants to thrive. Angiosperms, flowering plants, appeared for the first time during the Cretaceous period about 122 million years ago. During the Cretaceous period, bees and flowering plants evolved together. The flowers produced nectar and pollen. Bees and other insects collected the nectar and pollen as food.

Without bees, flowering plants self-pollinated when pollen from one flower reached the stigma of another flower from the same plant. While collecting nectar and pollen, bees carried pollen from one flower to many other flowers from other plants. This process is called cross-pollination. Cross-pollination created many new species of plants. The plants best designed to attract bees reproduced the most. Similarly, the bees with the best design for collecting nectar and pollen survived and reproduced the most. So, angiosperms and bees evolved together.

Birds

Birds were also evolving. By the end of the Cretaceous period, birds had replaced pterosaurs in the sky. Unlike pterosaurs, who were flying reptiles, birds evolved from dinosaurs. Feathers, common to both birds and some dinosaurs, are believed to originally have been used for thermoregulation in the warm climate of the Cretaceous period.

Dinosaurs

Many sauropods had gone extinct during the Jurassic-Cretaceous extinction event, but Apatosaurus and Diplodocus survived until the end of the Cretaceous period. Iguanodons, Ankylosaurus, and Tyrannosaurus rex appeared for the first time during the Cretaceous period. By the end of the period, all dinosaurs would go extinct during the Cretaceous-Tertiary mass extinction.

Mass Extinction

In 1979, a geologist found a layer of gray clay and shocked quartz separating the Cretaceous and Paleogene periods. This layer of clay was also found in other sites all over the world. The gray clay was full of iridium, a metal that is rare on Earth but common in asteroids. Shocked quartz is formed when rocks are suddenly vaporized and then cooled.

The Chicxulub crater in the Yucatan was created by a six-mile-wide asteroid that hit the Earth sixty million years ago, the same time period as the global layer of clay and quartz. Scientists believe the asteroid hit the Earth and wiped out everything around it. It also triggered tsunamis and volcanic eruptions all around the globe. Tons of rocks and ash were thrown into the sky. When the hot rocks fell back to Earth, they started forest fires.

Scientists believe the debris from the asteroid impact blocked all sunlight for two years. The temperature on Earth plummeted. Plants and the animals that depended on them died. The massive dinosaurs couldn’t find enough to eat, so they died. Only smaller organisms, such as the rodent-like mammals living among the trees, could survive this disaster.

Survivors

All plants and animals alive today have an ancestor that survived the mass extinction. Birds, lizards, snakes, frogs, crocodiles, turtles, plants, and mammals all managed to endure through the harsh conditions during and after the asteroid impact. The environmental niches left behind by the dinosaurs created new opportunities for the remaining organisms in the Cenozoic era.

Cretaceous Period Picture Book

Looking for another way to learn about the Cretaceous Period? Check out this picture book version. The pages are a part of my Earth History bundle on Teachers Pay Teachers.