1. Table of Contents Fossils The Relative Age of Rocks Radioactive Dating The Geologic Time Scale Early Earth Eras of Earth’s History A Trip Through Geologic Time

2. Wyoming, 50 Million Years Ago Today, Wyoming has areas of dry plateaus, but 50 million years ago it was very different. Fossils

3. The diagram below shows rock layers found at a site. Identify the area on the diagram that shows an intrusion. What is the oldest layer of rock in the diagram? The Relative Age of Rocks

4. Index Fossils Scientists use index fossils to match rock layers. Match the rock layers in locations 2, 3, and 4 with first area shown. Which fossils can be used as index fossils? The Relative Age of Rocks

5. Unconformities and Folding What are the oldest and youngest layers in the last two diagrams? Identify the unconformity. Which is the part of the fold that is overturned?

6. Radioactive Dating Half-Life The half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay. What pattern do you see in the graph? Use the pattern to complete the last bar.

7. Elements Used in Radioactive Dating Radioactive Dating

8. Earth's History in a Day If all of Earth's 4.6-billion-year history could be squeezed into one 24- hour day, it would have been a timetable something like this. The Geologic Time Scale

9. The divisions of the geologic time scale are used to date events in Earth’s history. What is the duration of each period? The Geologic Time Scale

10. Early Earth This artist’s illustration shows Earth shortly after the moon formed. Earth was hot and volcanic, and contained no liquid water. The moon was much closer to Earth than it is today. Over time, Earth’s surface began to cool, forming solid land.

11. Development of the Atmosphere The illustration shows the difference between Earth’s first and second atmospheres. What is the missing information for each atmosphere? Early Earth

12. Eras of Earth’s History Cambrian Life The illustration shows one artist’s idea of what Anomalocaris (the large organism) and other organisms looked like.

13. Eras of Earth’s History Changing Landscapes How do the organisms of each period differ and what are their characteristics?

14. Eras of Earth’s History The illustrations show a flying reptile called Dimorphodon and one of the earliest birds, Archaeopteryx. What do the two animals have in common and how are they different?

15. The End of the Dinosaurs Many scientists hypothesize that an asteroid hit Earth near the present- day Yucatán Peninsula, in southeastern Mexico. Eras of Earth’s History

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