Our formed about 4.5 did not all live billion ago. That’s a really, really during the same geologic . Stegosaurus became extinct long ago! To help picture it, imagine the entire FUN FACT 66 million years before history of the Earth squeezed into just twelve , from Tyrannosaurus rex walked noon to midnight. When we think of time in this way, the Earth. have only been around for about a minute!

12:00 pm 11:23 pm 11:59 pm 4.5 230 million years ago 150,000 years ago ago the Earth the fi rst dinosaurs modern humans formed appeared appeared

To describe Earth’s vast history, scientists use a geologic timescale. They divide it into long segments of time called eras. Each era is further ERAS PERIODS divided into periods. Cenozoic Quaternary 2 mya to present Earth events and characterize each era and period. For example, the Mesozoic Era starts after an event that wiped out Tertiary almost 90% of on Earth. Dinosaurs then fl ourished until the end 65-2 mya of the Mesozoic Era, which is marked by another major . Mesozoic Cretaceous Most dinosaurs went extinct but one group of dinosaurs——survived. 145-65 mya Jurassic Working in a small team, you will create a poster presentation about one 200-145 mya of the periods. You can use classroom and library resources, as well as the Internet to research the following information: 250-200 mya 1. Landmasses 3. Earth Events Paleozoic What did the of the What major Earth events occurred 300-250 mya Earth look like? Illustrate the during the period? Was there arrangement of landmasses widely distributed volcanic activity, 360-300 mya and/or . an impact, or the forma- Devonian tion of large belts? 420-360 mya 2. What was the climate like? 4. Organisms 445-420 mya Was there an age? Was it What and groups very warm? lived during the period? What Ordovician organisms became extinct? 490-445 mya Tips Cambrian • As a part of your presentation, illustrate a 12- clock and mark the span of the 540-490mya period on the clock. Hint: Each hour corresponds to 375 million years. Precambrian • Include photographs of plant and animal or artist renditions of organisms 4,500-540 mya that lived during the period.