1. Earth’s History: Fossils and Absolute Age

2. The Big Question: How do we know long life has existed on Earth?

3. Fossils Source: J. C. Carton/Carto/Bruce Coleman, Inc. New York Fossils are the remains or traces of prehistoric life. Fossils show the history of life on Earth and how different groups of organisms have changed over time

4. Fossil Formation What does a fossil need to form? 1.Organism needs hard parts 2.Rapid burial

5. Types of Fossilization

6. Precambrian Stromatolites www.geology.sdsu.ed Earliest Fossils…Calcium Carbonate deposits from algae

7. Cambrian Tribolites Source: Breck P. Kent

8. Paleozoic Brachiopods Source: Breck P. Kent

9. Paleozoic Plants

10. Mesozoic Ammonite Source: Ken Lucas/Biological Photo Service Natural Cast

11. Mesozoic Dinosaur www.fossils.com

12. Cenozoic Hominid et “LUCY” With 40 percent of her skeleton intact, Lucy remains the oldest and most complete adult human ancestor fully retrieved from African soil. (c) The Houston Museum of Natural Science Australopithecus afarensis

13. Relative vs. Absolute Dating Law of Superposition: in an undeformed sequence of sedimentary rocks, each bed is older than the one above it, and younger than the one below it.

14. Relative Dating Can determine relative age of rock layer and fossils Performed by estimating rock/fossil age compared with that of other rocks/fossils Drawbacks – provides no info about age in years

15. Absolute dating Can determine the absolute age in numbers Is performed by radiometric dating Drawback - part of the fossil is destroyed during the test

16. Fossils as a time indicator Index fossils are widespread geographically, are limited to a short span of geologic time, and occur in large numbers

18. Unstable Atomic Nuclei Decay Strong Force?

19. Radiometric Dating Radioactive Uranium breaks down into more stable Lead. Can be used to date materials billions of years old. U-238 has a “half life “ of 4.5 billion years.

20. Figure 8-18 Graph -- Radioactive Decay

21. Meteorites Date Earth Radiometric age of meteorites date the formation of the Solar System and Earth (4.55 billion years old) http://upload.wikimedia.org/wikipedia/commons/0/00/Crab_Nebula.jpg Crab Nebula

22. Carbon-14 Dating

23. Radioactive Carbon breaks down into more stable Nitrogen. Can be used to date materials only up to 75,000 years old. C-14 has a “half life “ of 5,730 years.

24. Geologic Time Scale on p. 365 GEOLOGIC TIME SCALE on page 365