Earth History Study Guide Name _________________ Period ____ 1. What type of rock would geologists most likely find evidence of past life forms? 2. Name some geologic events from this chapter. 3. The physical, chemical, and biological laws that operate today have also operated in the geologic past. What principle is this? 4. The present is the key to the past. This statement rephrases what principle? 5. According to the principle of cross-cutting relationships, an intrusive rock body is? 6. Nicolaus Steno proposed the most basic principle of relative dating, the law of ? 7. The dating process that places geologic events in proper sequence is what? 8. The law of superposition states that in an un-deformed sequence of sedimentary rocks, each layer is what? 9. Define Fossils? 10. In what type of rocks are most fossils found? 11. What environment does not usually have fossils? (types of layers) 12. What determines the type of fossil that is formed? 13. Petrified wood is what type of fossil? 14. The footprints of a dinosaur are what type of fossil? 15. What is important if an organism is to become a fossil? 16. Why would a worm stand a poor chance of becoming a fossil? 17. What is an index fossil? 18. The process by which atomic nuclei spontaneously decay is called? 19. The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope is called? 20. Atoms with the same atomic number but different mass numbers are called? 21. If you have 20g of a radioactive parent isotope. How many grams of parent isotope will be present in the same after 2 half-lives? 22. What is a half-life? 23. The radioactive dating of an igneous rock provides? 24. Radiocarbon dating is used to date? 25. Radiocarbon dating could be used to date what dates in time? 26. Geologists have divided Earth’s history into manageable units that are called? 27. What is the largest expanse of time on the geologic time scale? 28. Which eon of the geologic time scale means “visible life”? 29. The era of “ancient life” is known as? 30. List the geologic time scale in order from longest to shortest? Using Period Era Epoch 31. 88% of Earth’s history is within the expanse of time before the Phanerozoic Era called the? 32. List all of the Phanerozoic Eons? 33. When did abundant fossil evidence appear in the geologic record? 34. Describe Nicolaus Steno’s three principles used in relative dating?