e Geologie Time Scale Questions: 1. How many eons is the Geologic Time Scale divided into? What are they. 2. Based on the current geologic time scale, which eon lasted the longest? How many years? 3. How many eras have there been during the Phanerozoic Eon? What are they? 4. Which is the largest division of time an Eon. Era, or Period? 5. How many periods is the Paleozoic era divided into? The dinosaurs and many other species became extinct in a relatively short period of time that marks what is called the K-T boundary, which stands between the Cretaceous and Tertiary periods. About how long ago did the dinosaurs become extinct? 7. How long ago are the earliest forms of life believed to exist? 8. When did the first land plants exist? 9. What forms of living things characterized the Cambrian period? 10. During what period did humans first appear? 11. Imagine you found a fossil of a bird that dates to 213 million years. Why would this find be astonishing to scientists? answer in a complete sentence) 12. Suppose a geologist finds a layer of rock that can be dated to 320 million years ago. Layers from which periods would be expected to be above and below the newly discovered layer?