2. Can you name earth s three eras and explain why they are divided that way?

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1 Unit: 3 Earth s History LT 3.1 Earth s History: I can map out a basic history of the earth, including key events. 1. Can you place the key events of earth s history in order? #1 Yes I can: 2. Can you name earth s three eras and explain why they are divided that way? LT 3.2 Absolute Dating: I can explain and calculate the age of a sample using radioactive decay. 1. Can you explain radioactivity and how its decay is used to determine its age Yes I can: 2. Can you explain half-life? 3. Can you explain absolute dating? LT 3.3 Relative Dating: I can explain how radioactive dating is used along with the law of superposition to determine the age of different events in geological history. Yes I can: 1. Can you explain the law of superposition? 2. Can you explain the law of crosscutting relationships? 3. Given a cross-section of the earth, can you place the layer and events in order?

2 Vocabulary I should know: #2 1. Mass Extinction When many species die off in relatively the same time period. Usually caused by some quick global climate change. 2. Era a long time period in history. It is a major division of an eon and is divided by periods 3. Radioactive an unstable atom (usually a large one) the breaks apart into smaller atoms. This occurs at a predictable rate so it can be used to determine the age of rocks and therefor the things found in the rocks. 4. Half-life the amount of time it takes for half a radioactive substance to decay. (C-14 is 5730 years which means every 5730 the amount of C-14 is cut in half.) 5. Parent Isotope What a radioactive isotope starts off as 6. Daughter Isotope what a radioactive isotope turns into 7. Relative Dating aging thing relative to other things. Does not tell the actual age, only the order in which things happened. 8. Absolute Dating finding the exact age of something. This rock is 200 million years old is an example. 9. Law of Original Horizontality the idea that layers of sedimentary rocks always form (or start as) horizontal layers 10. Law of Superposition - a law that states that the layer on the bottom is always older than the layers above it (assume they are undisturbed) 11. Law of crosscutting relationships something (fault line, igneous intrusion) has to be younger than layers of rock that is cross over/through. 12. Unconformity when there is a gap in time (missing layers) between layers of rock 13. Disconformity when there is an unconformity between layers of sedimentary rock 14. Nonconformity when there is an unconformity between igneous/metamorphic rock and sedimentary rocks above it. 15. Angular unconformity - when there is an unconformity between angled layer of sedimentary rock and horizontal layers of rock 16. Index Fossil a fossil that only lived during a certain time period, so if found, can narrow down the age of the layer of rock is found in to the time in which that fossil existed.

3 Geologic History Timelines LT 3.1: I can map out a basic history of the earth, including key events. #3 Procedure: Plot the following events from Earth's History onto BOTH of the timelines to the right.

4 Age of the Earth LT 3.1: I can map out a basic history of the earth, including key events. #4 1. What are the three main eras of life on earth? 2. What types of animal are each known for? 3. What is the name of the period of time before the eras? 4. Each era ends in what type of event? 5. Here is a list of important developments in the earth s history. Place them in order from first to last. a. Dinosaur extinction b. Permian extinction (Pangaea) c. First Life d. First man hominids show up. e. Earth forms f. The Last ice age g. Formation of oxygen atmosphere 6. Find two ways to supports the statement most life-forms that existed on the Earth have become extinct. 7. What is the longest section of the Earth History?

5 Radioactivity and Half-life #5 LT 3.2: I can explain and calculate the age of a sample using radioactive decay. 1. Radioactivity - An atomic nucleus emits a form of radiation to become stable. In other words, the nucleus decays into a different atom. 2. Radiometric dating - Determine age by comparing to ABSOLUTE DATING 3. Half-Life - Amount of time it takes for of a sample of radioactive atoms to decay 4. Different isotopes for different lengths of time Isotope Half-Life Time range 5,730 year 70,000 or less 1.25 Billion 50, Bill 704 Million 10 mill 4.6 bill 4.5 billion 10 mill 4.6 bill 1.25 billion 10, Bill 5. Why use carbon 14? 1. You have 400 mg of a radioisotope with a half-life of 5 minutes. How much will be left after 5 minutes? 2. You have 1000 mg of a radioisotope with a half-life of 5 minutes. How much will be left after 10 minutes? 3. You have 32 mg of a radioisotope with a half-life of 10 minutes. How much will be left after 30 minutes? 4. You have 25g of the parent isotope and 75g of the daughter isotope. a. How many total parent isotopes did you start with? b. How many ½ lives have gone by? 5. Half-Life Calculation # 5 6. Half-Life Calculation # 6 7. Half-Life Calculation # 7

6 8. LT 3.2: I can explain and calculate the age of a sample using radioactive decay. Half-life of Licoricium Lab Follow Mr. Potter s directions to complete the following activity: #6 Absolute age:

7 Half-life Questions #7 LT 3.2: I can explain and calculate the age of a sample using radioactive decay. 1. The approximate half- life of the sample in graph is a. 350 years b. 200 years c. 400 years d. 550 years 2. Quick review: Which of the following happened first on earth? a. Ice ages b. Oxygen atmosphere c. First life d. Dinosaur extinction Here are some problems you will need to be able to work out. Use the chart below to answer the following questions: Parent molecule Daughter molecule Half-life Carbon-14 Nitrogen-14 5,730 years Potassium-40 Argon billion years Uranium-235 Lead million years Uranium-238 Lead billion years 3. If you have 20 grams of Carbon-14, about how long will it take to decay into 5 grams? a. In the previous question, how much Nitrogen-14 will you have when the carbon gets down to 5 grams (assuming you had none to start)? 4. If you have 64 grams of Uranium-238, how much will you have after 13.5 billion years? 5. If you have 16 grams of Potassium-40, how much will you have after 5 billion years?

8 Parent molecule Daughter molecule Half-life Carbon-14 Nitrogen-14 5,730 years Potassium-40 Argon billion years Uranium-235 Lead million years Uranium-238 Lead billion years #8 6. If you find a rock that has 20g of Carbon-14 and 60 grams of Nitrogen-14, how old is it? 7. If you find a rock that has 10g of Uranium-238 and 70g of Lead-206, how old is it? 8. If you have 100 grams of Uranium-235, how long will it take to reach 12.5 grams? 9. Why is Carbon-14 pretty useless to age dinosaur fossils? 10. Licoricium has a half-life of about 20 years. So, after 20 years, half of the Licoricium turns into Tastyium, the daughter element. a. How long will it take for Licoricium to go from 100 grams to 12.5 grams? b. If you have 240g of Licoricium, how much will you have after 60 years? c. You find a rock. It contains 7 grams of Licoricium. We also discover that there are 49 grams of Tastyium. If we assume (and we should) that all of the Tastyium started off as Licoricium, how old is the rock? Show your work.

9 #9 Relative Dating LT 3.3: I can explain how radioactive dating is used along with the law of superposition to determine the age of different events in geological history.

10 #10 Type Example Description Nonconformity Angular unconformity Disconformity Put what happened in order: U S M W K B

11 Relative Dating Put the events in order from first to last. #

12 #

13 #13 Potter Name: Date: Hour: LT 3.3: I can explain how radioactive dating is used along with the law of superposition to determine the age of different events in geological history. Index Fossils 1. If you find a photo with teachers X, Y and Z, what year is it from? 2. If you find a photo with teachers X, Z and Q, what year is it from? 3. If you find a photo with teachers X, Y but not Z, what year is it from? Does it matter that Mrs. Z is not in the picture? 4. If you find a photo with teachers X and Z, what year is it from? 5. What makes it easy to identify when the picture was taken? 6. What makes it difficult? 7. Take a look at the picture to the right. The top section has a series of fossils, some of the fossils span a large time frame. But there is only a small time frame when they can be all found together, much like our teacher in the yearbook analogy. Index Fossils Fossils that are used to age the layer of rock that found in. Good index fossils are made from organism that only lived for a short time and are found in a widespread area. The picture to the right shows different fossils during the geologic time period in which they lived. 8. If you found a shark tooth fossil in the rock, what does that tell you about the age of that rock? 9. If you found a trilobite in the first layer (bottom) of rock and an echinoid in the second, what does that tell you about happened in between? 10. Could you ever find a shark tooth in a layer of rock below a trilobite? Why?

14 Part I, Lab: Make a fossil range chart. Look at the pictures of fossils in figure 1. Underneath each picture is a time range. You will make a bar graph below by shading in the area that represents the time period during which the fossil existed. For instance, for the Goniatites, shade in everything from the Mississippian to the Pennsylvanian. When this is complete, you will have made a fossil range chart. Data Analysis 1. If you have a rock that has a Ceratite in it what time period(s) is it from? How do you know? 2. If you have a rock that has a Goniatite and a Nautiloid what time period(s) is it from? 3. If you have a rock that has an Ammonite and an Orthocone in it, what time period(s) is it from? 4. If you find a rock that has an Orthocone what time period(s) is it from? 5. Which fossils might you expect to find in a rock of Jurassic age? 6. Which fossil(s) make the best index fossils? Part II 7. Look at the following diagrams of fossils that can be found in rocks. Identify the fossils using the pictures in figure 1. Then determine the age of each rock. 8. Cephalopods are organisms that lived in the open ocean. During the Cretaceous, a lack of oxygen in ocean basins meant that large deposits of organic material built up. This material came primarily from microorganisms in the ocean water. This material was later buried and eventually became oil. Geologists from oil companies frequently use range charts to help them date rocks so that they might find more oil. Imagine that you are an oil geologist. Of the rocks you dated in question 8, which would you recommend further investigation for oil?