1. Geologic Time 10/29 – 10/31

2. Bell Ringer Monday 10/29/2012 ● What types of things do you think might mark the end of a geologic era?

3. Era-Ending Events ● Natural disaster (e.g. meteor) ● Climate change (e.g. ice age) ● Mass extinction and rise of new predominant animal species

4. Fossil Evidence for Change ● Fossils represent remains of once-living organisms, many of which are now extinct. ● Kinds of fossils found in rocks of different ages differ because life on Earth has changed over time.

5. Classwork ● You will be completing “Who's On First?” procedure B. Please begin by reviewing the handout on the Law of Superposition.

6. Bell Ringer Tuesday 10/30/2012 ● What facts do you know about this animal? Come up with as many as you can think of. Try to think of both physical characteristics and behaviors.

7. Brainstorming... Properties of a Horse

8. Follow-up... ● What would you know about this animal if it was extinct and you only had fossil evidence to learn about it?

9. Fossil Evidence: Stegosaurus ● What do we know about fossilized animals like this one? What can you infer about it based on fossil evidence?

10. Classwork ● Read “Death of the Dinosaurs” article and answer comprehension questions on a separate sheet of paper.

11. Absolute Age Dating Outline: ● What is absolute age dating? ● What is radiometric dating? ● Review: what is an isotope? ● What is a radioactive isotope? ● What is half life? ● Why use Carbon-14?

12. What is absolute age dating? ● Absolute-age dating enables scientists to determine the actual age of a rock, fossil, or other object.

13. What is radiometric dating? ● Scientists attempt to determine the ratio of 'parent nuclei' to 'daughter nuclei' within a given sample of a rock or fossil. ● This ratio is then used to determine the absolute age of the rock or fossil.

14. Radiometric Dating ● Radiometric dating works because certain isotopes of atoms are radioactive, which means they decay into other kinds of elements. ● A specific element does this in a predictable time, called the half life, which is how scientists use the ratio of parent and daughter nuclei to determine age.

15. Review: what is an isotope? ● An isotope is an atom of a given element with a different number of neutrons but the same atomic number (which is the number of protons) ● For example, U-237 and U-238 are both uranium and have atomic number 92, but have different mass numbers (237 and 238) which means different numbers of protons.

16. What is a radioactive isotope? ● A radioactive isotope is an isotope of an element that decays and emits radioactive particles to become another type of element. ● For example, Carbon-14 decays into Nitrogen- 14

17. What is half-life? ● Half-life measures the amount of time it takes for half of a radioactive isotope sample to decay into its product. ● For example, Carbon-14 has a half-life of 5730 years. So if you start with 100 grams of Carbon-14, after 5730 years there will be 50 grams of Carbon-14 and 50 grams of Nitrogen- 14.

18. Why use Carbon-14? ● Carbon is especially useful for finding the age of materials that are of organic origin, such as amber, humanoid bones, papyrus, and charcoal fragments, because all organic materials contain carbon. ● Uranium is particularly useful for very old materials because its half-life is very long (700,000,000 years).

19. Carbon-14 Carbon-14 has atomic number 6 and atomic mass 14 ● How many protons? _____ ● How many neutrons? _____ ● How many electrons? _____

20. Exit Slip: Answer Questions & Turn In ● Why use carbon for dating? ● How did I figure out that 25% of the original amount of carbon in a sample is left after two half lives go by? ● What is the difference between relative and absolute age dating? ● HOMEWORK: BRING TEXTBOOK FRIDAY!