1. Chapter 12

2. Warm-up9/1/15  List and briefly describe three different types of fossils.

3. How old is the Earth thought to be? It is estimated that the earth is 4.6 billion years old, but how do we come to this conclusion???

4. Rocks Record Earth History  Rocks record events and changing life forms of the past.

5. James Hutton  18 th century physician and farmer who made valuable observations about the geologic changes occurring in his area

6. Uniformitarianism  His “studies” led to the Principle of Uniformitarianism (the forces and processes observed today have been happening for a long time)

7.  The processes are the same, but they may occur at different rates

8. Catastrophic Theory  Before Hutton’s time, it was believed that the earth was 4,000 years old and formed from some sort of catastrophe

9. Earth as a History Book  Think of the rock layers of the earth as pages in a history book

10. Relative Age vs. Absolute Age  Relative age is the age of an object compared with the ages of other objects  Strata—layers of rock

11. Nicolaus Steno  Developed three observations that are the basis for relative dating of Earth’s history.

12. Types of Relative Age Dating  Law of Superposition—an undeformed sedimentary rock layer is older than the layers above it and younger than the layers below it.

13. Original Horizontality  Layers of rock are deposited in a horizontal fashion.

14. Crosscutting Relationships  Law of Crosscutting Relationships— principle that a fault or intrusion is always younger than the rock layers it cuts through

16. Unconformities  It is a break in the geologic record created when rock layers are removed by erosion

18. Quiz 1. How old is the earth thought to be? 2. What is the Principle of Uniformitarianism? 3. What is the Law of Superposition? 4. What is the Law of Crosscutting Relationships?

19. Absolute Age  Absolute age  the actual age of the rock

20. Types of Absolute Dating  Rates of Erosion and Deposition  scientists measure the rate of erosion of a stream and back track how many years ago the stream must have been there to have eroded as much as it has  Only practical for about 10,000 to 20,000 yrs ago

21. Radioactive Decay  The comparisons of the amounts of the parent material (the one you started with) and the daughter material (the one produced through nuclear decay)

22. Radioactive Decay  The amount of time it takes for the exactly one half of the parent material to decay to the daughter material is called the half-life. Scientist use this unchanging time to date a substance.

23. The Fossil Record  Paleontologists  scientists who study fossils to learn about the earth’s past  Paleontology  the study of fossils

24. Preservation of Organisms  Mummification  preservation of dead organisms by drying

25.  Amber  preservation of insects in hardened tree sap

26.  Tar beds  preservation of animals in beds of thick petroleum that oozes to the earth’s surface (tar)

27.  Freezing  preservation of animals or organisms in low temperature soils and ice

28.  Petrifaction  process in which organic materials are replaced by minerals

29. Traces of Organisms  Trace Fossils: tracks, footprints, borings, and burrows

30.  Imprints, molds, and casts

31.  Coprolites  the fossilized dung and waste materials of animals

32.  Gastroliths  stones found in animals like dinosaurs that helps them to digest food

33. Interpreting the Fossil Record  Fossils are used to date rocks  It can reveal changes in the environment

34. Index Fossils  Certain fossils found exclusively in rock layers of a particular geologic age  For example, trilobite fossils from the Paleozoic Era

35. Another index fossil  Ammonite fossil from the Mesozoic Era