Chapter 18: The History of Life on Earth 1. Why were dragonflies so much larger 300 million years ago? 2. How are sedimentary rocks formed? 3. Order these geological periods from the most ancient to the most recent: (a) Devonian (b) Cambrian (c) Jurassic (d) Silurian (e) Cretaceous 4. What type of evidence do scientists have to support the idea that a giant meteorite hit the Earth at the end of the Cretaceous period? 5. What is the difference between fauna, flora, and biota? 6. What is an amniote? Are amniotes vertebrates? 7. What is the difference between climate and weather? 8. What is causing global warming?.