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Warm Up What do you think the Earth looked like 5 million years ago? 200 mya? 2,500 mya? Objective: SWBAT Describe one defining feature for each of the 4 geological eras Agenda: Notes: 4 Geological Eras Class Geologic Timeline Guided Notes: Relative Dating Index Fossil Activity Closing Homework: Relative Dating Packet Notes: 4 Geological Eras Precambrian (4.6 bya—600 mya) No life on land, just in water (algae, fungi, worms) Paleozoic (600 mya—250 mya) First fish and trilobites, land plants and animals (spiders and scorpions), amphibians and reptiles Permian extinction—biggest extinction with 90% species dying off Mesozoic (250 mya—65 mya) First birds, dinosaurs, and mammals Cretaceous extinction—dinosaur extinction 65 mya caused by crater off of Mexico’s Yucatan Peninsula Cenozoic (65 mya—present) Many new mammals, including humans Geologic Timeline As a class we will follow the directions on our geologic timeline worksheet to create a geologic timeline for Earth! Notes: How Scientists Determine Geologic Timeline Index fossils—traces of unique, abundant, and widespread ancient life that are characteristic of a given time period Relative dating—placing events in sequence they occurred (doesn’t nail down exact time period!) 5 Principles: Principle of Superposition: horizontal layers (strata) at bottom are oldest Principle of Horizontality: rock layers are originally deposited horizontally Principle of Cross-cutting Relationships: diagonal layers (intrusions) are always younger than the strata they cut across Principle of Included Fragments: embedded rocks are older than the mixture that surrounds them in a strata Principle of Unconformity: erosion causes missing geologic record Class Practice Which fossil would make the best index fossil and why? Class Practice Which fossil would make the best index fossil and why? Y Z X Y Z Y Y Y Z Y Z Y X Class Practice List the order in which these sandwich layers were deposited starting with the oldest **Assume the sandwich was not flipped over. Class Practice Which law tells us that the chocolate chips were placed inside the cookie BEFORE it was baked? Index Fossil Activity! Working with the person next to you, follow the directions to model the idea of index fossils Each card you are given represents a strata or layer of rock Whatever is found in the first strata will be found in the strata that lays next to it Layer your cards so that this is true Closing What is one limitation of relative dating? Warm Up Organize the following eras in order of oldest to youngest. Then, match the era with its defining characteristic. 1. Precambrian 2. Cenozoic 3. Paleozoic 4. Mesozoic a. No life on land, just algae and fungi b. Fish, trilobites, and first life on land (spiders) c. Dinosaurs, birds, small mammals d. Big mammals, humans Objective: SWBAT Calculate the age of a material given it’s amount of radioactive decay and the radioactive element’s half-life Agenda: Finish Index Fossil Activity (10 minutes) Review Relative Dating Packet (5 minutes) Notes: Absolute Dating (10 minutes) Twizzler Lab (15 minutes) Carbon Dating Article Summary (45 minutes) Closing (5 minutes) Homework: Earth’s History Quiz Review due Friday (Quiz is Friday) Begin Midterm Review Finish Index Fossil Activity! Layer your Set B fossil cards from oldest (card M) to youngest Remember: Each card you are given represents a strata or layer of rock Whatever is found in the first strata will be found in the strata that lays next to it Then, record the order of your cards from youngest to oldest using the letter in the lower left hand corner Which fossil would be a good index fossil? A bad index fossil? Why? Review Relative Dating Packet Follow along as we review your relative dating packet! Transition What is one limitation of relative dating? Notes: Absolute Dating Finds exact age! Many objects contain radioactive elements EX: carbon-14, uranium-238, rubidium-87, and potassium40 These radioactive elements decay (or change to nonradioactive elements) over time Scientists can measure the amount of decay (or the ratio of radioactive to non-radioactive elements) to determine age This is because each radioactive element has a specific half-life—the amount of time it takes for 50% of the radioactive elements to decay Class Practice—Write in Notes! U-238 has a half-life of 4.5 billion years. You find a mineral made up of 1/2 of its original radioactive U-238 content. How old is this mineral? Class Practice You have found the remains of an early human, which contains 1/4 of its original radioactive C-14 content. C-14 has a half-life of approximately 6000 years. How old are these remains? Class Practice You have discovered a meteorite with 1/8 of its original radioactive K-40 content. K-40 has a halflife of approximately 1.2 billion years. How old is this meteorite? Twizzler Lab! Follow your directions to model radioactive decay with twizzlers Carbon Dating Article Summary! Please put everything away except for a writing utensil and a sheet of lined paper Read the article given, annotating in the margins after each paragraph Then, write a summary of the article using your annotations Use your rubric and our class tips as a guide When you finish, reread your summary to ensure its completeness While reading: Stop after each paragraph and jot notes in margin Circle or underline important words Highlight important phrases After reading: If someone were to ask you what the article was about in one sentencethat is your topic sentence Look to margin notes for supporting details Concluding sentence= summary of topic sentence and three supporting details Other: Do not plagiarize---use own words! This means no need for quotes or citations! Do not use vague words! After finish, reread your summary for mistakes and adjust accordingly Closing Another scientist has discovered ancient cloth that appears to be over 1 million years old. He asks you to perform C-14 dating on the cloth (Remember: C14 has a half-life of about 6000 years.) However, you tell him you are unable to do so. Why is this?
