Mesozoic Era: 251–65 Million Years Ago

The Mesozoic Era was the time of the dinosaurs. The first dinosaurs appeared about 225 million years ago. About this same time, Pangaea began to break up. The first mammals, which evolved from warm-blooded reptiles, also appeared in the Mesozoic. Many areas had a warm, wet climate. Another major development was the appearance of flowering plants.

All the dinosaurs and many other types of organisms were killed at the end of the Mesozoic Era. What caused this mass extinction?

A spiral diagram (shaped like a coiled snake) showing the history of the Earth, and major things that happened during each era.

Figure 36 This spiral diagram provides an overview of Earth's history. Start at the bottom left, which begins with Earth's formation approximately 4. 6 billion years ago. Then follow the spiral upward to see many of the major events in the history of life and geology on Earth. Interpreting Diagrams During what era did small mammals first appear?

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Table of Contents

Physical Science CHAPTER 1 Science Skills CHAPTER 2 Properties of Matter CHAPTER 3 States of Matter CHAPTER 4 Atomic Structure CHAPTER 5 The Periodic Table CHAPTER 6 Chemical Bonds CHAPTER 7 Chemical Reactions CHAPTER 8 Solutions, Acids, and Bases CHAPTER 9 Carbon Chemistry CHAPTER 10 Nuclear Chemistry CHAPTER 11 Motion CHAPTER 12 Forces and Motion CHAPTER 13 Forces in Fluids CHAPTER 14 Work, Power, and Machines CHAPTER 15 Energy CHAPTER 16 Thermal Energy and Heat CHAPTER 17 Mechanical Waves and Sound CHAPTER 18 The Electromagnetic Spectrum and Light CHAPTER 19 Optics CHAPTER 20 Electricity CHAPTER 21 Magnetism CHAPTER 22 Earth's Interior CHAPTER 23 Earth's Surface CHAPTER 24 Weather and Climate CHAPTER 25 The Solar System CHAPTER 26 Exploring the Universe Skills and Reference Handbook