Geologic Time Scale

1. Geologic Time Scale

2. Measuring Time • The Earth has existed for 4.6 billion years • The geologic time scale divides all those years into sections • Like how your science book is divided into Units, then Chapters, then Sections, then Pages • Each section is unique because it shows a specific change in life or in the Earth’s surface

3. Giving Time a Name • The largest sections are called “eons” • “Eons” are divided into “eras” (the 2nd largest section) • “Eras” are divided into “periods” • Then “periods” are divided into “epochs” • Usually the oldest sections are shown on the bottom and the most recent sections are shown on the top

4. How is Time Divided? • Major changes in Earth’s history mark the boundaries between the sections • Most sections have been divided because a major organism developed or went extinct.

5. Precambrian Time

6. Pre- Cambrian Time • Oldest and Longest Time Period • Almost 90% of Earth’s History • From beginning of Earth (4.6 billion years ago) to 540 Million years ago • Oldest rocks are the deepest rocks • Ores are deposited (iron, silver, gold)

7. Paleozoic Era • Began 542 million years ago and ended 251 million years ago • Divided into 6 periods • Many new life forms appeared during the 1st period, the Cambrian Period = “Cambrian Explosion” • For the first time on Earth, organisms had hard parts (shells, exoskeletons) • Some organisms that were alive during this period still exist today (ferns and salamanders) but they were giants!

8. Phanerzoic Eon, Paleozoic Era • Paleo- (Latin) ancient; -zoic (Latin) animals/ life • Hard shelled animals appear • Pangea formed • Plants begin to grow on land • “Age of Fish” large fish populate oceans • Amphibians (frogs) go to land • Insects appear

9. Permian Extinction • The largest mass extinction happened 251 million years ago • Marked the end of the Paleozoic Era and the start of the Mesozoic Era • Scientists are not sure what caused this mass extinction (maybe climate change & volcanoes) • 90% of ocean life and 78% of land life died • Reptiles and amphibians survived!

10. Paleozoic Con’t • Pennsylvanian Period- very large swamps which later become coal • Appalachian Mountains Form

11. Mesozoic Era

12. Mesozoic Era • Began 251 million years ago • Surviving reptiles and amphibians evolved into many other species (like dinosaurs) = “Age of Reptiles”

13. Mesozoic Era • Meso- “middle” -zoic “animals/life” • Breakup of Pangea • Age of Reptiles- dinosaurs and reptiles rule planet • Rocky Mountains form

14. Cretaceous-Tertiary Extinction • Another mass extinction happened 65 million years ago • Marked the end of the Mesozoic Era and the beginning of the Cenozoic Era • All of the dinosaurs and half of the other animals & plants went extinct • Scientists think an asteroid hit Earth, the dust clouds blocked out the sun, plants died, then herbivores, then carnivores.

15. Mass Extinction • Dinosaurs are killed by meteorite • Animals and plants change • 90% of all species that have ever lived are now extinct

16. Cenozoic Era

17. Cenozoic Era • Began 65 million years ago and continues today • Scientists know the most about this Era because the fossils are in the top rock layers and are easier to find • Land & climate has changed a lot • What big change will happen that will end this era & start the next?

18. Cenozoic Era • Ceno- “new”; -zoic “life” • Last 45 million years • Age of Mammals- Humans evolve • Ice Ages • Flowering Plants • Colorado Plateau and Sierra Nevada Mountains formed