Digging for Dinosaurs

Digging for Dinosaurs — page 3
chapter 1 WhAt ArE DINOSAURS Dinosaurs are a group of reptiles that first walked Earth around 240 million years ago They lived during the Mesozoic Era which ended about 65 million years ago At this time an event occurred on Earth that killed many of the planet’s species including dinosaurs Scientists are still not certain what event caused this destruction The most popular theory is that an asteroid hit Earth and covered its surface with ash The resulting conditions killed plant life as well as many animals that depended on plants From then on dinosaurs were extinct DiG ThIs Over years of research scientists have learned that dinosaurs were a varied group The smallest species was the size of a chicken The largest was nearly as long as three school buses Today dinosaur fossils are found in rock all over the world Paleontologists determine the age of these fossils using radiometric dating This 6