Relative Dating - Philippine Science High School - 2020 PDF

Philippine Science High School Earth Science Learning Guide Guide Code: 11.0 Earth’s Geologic History Lesson Code: 11.1 Relative Dating Time Limit 30 min TARGET...

Philippine Science High School Earth Science Learning Guide Guide Code: 11.0 Earth’s Geologic History Lesson Code: 11.1 Relative Dating Time Limit 30 min TARGET Learning where to get the information is quite a basic. You are now stepping up to scrutinizing what you have gathered. After completing this module, you are expected to: A. Distinguish the different principles used in relative dating and unconformities B. Differentiate and utilize the different laws used in relative dating, and sequence the events that happened in the geologic past. C. Identify the significance of relative dating principles and unconformities in understanding earth’s history HOOK Look at the photos of each subject below, and try to answer the questions that follow: Figure 1. Person A Figure 2. Person B ("Hoi An" by davemelbourne is ("Young Lady in Brisbane Mall-1=" by licensed under CC BY-NC 2.0. To Sheba_Also 17.5 Mil + views are view a copy of this license, visit licensed under CC BY-SA 2.0. To https://creativecommons.org/license view a copy of this license ,visit s/by-nc/2.0/) https://creativecommons.org/licenses/ by-sa/2.0/) Among the photos of two women shown, which one do you think is older? What physical trait did you use as basis to determine which one is older? Earth Science Relative Dating Page 1 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  Figure 4. Person D Figure 3. Person C ("IMG_1700" by Tiffany Joyce is ("Grumpy baby" by renzfelipe is licensed under CC BY-NC-ND 2.0. licensed under CC BY-NC-ND 2.0. To view a copy of this license, visit To view a copy of this license, visit https://creativecommons.org/license https://creativecommons.org/licens s/by-nc-nd/2.0/ es/by-nc-nd/2.0/) Among the two baby pictures shown on the left, which one do you think is older? Which physical trait dictates that the other one is older? Analysis: As an introductory activity for this topic, the game shows us that on the first batch of photos, the age gap between the two individuals can be easily recognized. However, identifying the difference in age between the two babies can be quite challenging. In the study of earth’s geologic history (e.g. rock age), without the aid of advance technology that we use now in this modern era, earth scientists had to really on a more practical approach in the study of earth’s history. For example, the law of Superposition means that, in an undisturbed and or undeformed sequence of rock layers, the older rock is at the bottom. The idea may be common sense to us now, but it was very useful in analyzing on how different events occurred in nature. However, same with analyzing the age distinction of the babies in the photo using relying only in the observable traits has its limitation. IGNITE In determining the age of rocks and rock layers, different techniques may be used. The actual, specific age of some rocks may be determined using radiometric dating, otherwise known as absolute dating. In radiometric dating, isotopes of certain elements found in minerals are used to know the time when the rocks were formed. You may know more about this in your advanced Chemistry class. You may have heard some of the techniques used like Carbon dating (C-14) and Uranium-Lead dating (U-Pb) For now, what we will be using is relative dating. Earth Science Relative Dating Page 2 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  Relative Dating Principles For this portion, we will be discussing the different principles/laws involved in the study of Earth’s Geologic History. Take note that we will be only discussing the principles/laws used in determining the relative ages, which means that they do not show the actual or absolute age (e.g. the absolute age of the earth is roughly 4.7 billion years old), but only determine the sequence of events that took place (e.g. the moon is younger than earth). A. Law of Superposition Formulated by Nicolas Steno (1638-1686), a Danish anatomist, the law simply states that, in an undeformed or undisturbed layer of sedimentary rocks, the rock layer found at the bottom is the oldest, and consequently, the youngest rock layer is found at the top. In the sequence of rock layers (also known as strata) shown in Figure 6, the younger rock layers overlay the older strata in the Grand Canyon. Figure 5. Nicolas Steno (Medical Heritage Library, Inc. is licensed under CC BY-NC-SA 2.0. To view a copy of this license, visit https://creativecommons.org/licen ses/by-nc-sa/2.0/) Younger Older Figure 6. Portion of the Grand Canyon, USA ("IMG_9766" by jay8085 is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/ Earth Science Relative Dating Page 3 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  B. Law of Original Horizontality While observing the deposition of sediments during floods, Steno observed that thin layers of sediments were deposited in a horizontal manner. This observation allowed him to formulate the Law of Original Horizontality, which states that sediments are generally deposited in a horizontal manner. Which means that if you observe tilted sedimentary rock layers or strata, it means that it was disturbed by geologic forces in the past. Figure 7. Previously horizontal sedimentary layers deformed by past geologic events ("Rock Folds" by jwbenwell is licensed under CC BY-ND 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nd/2.0/) C. Principle of Lateral Continuity This third principle formulated by Steno, the principle of Lateral Continuity states that, sedimentary rocks and/or sediments extends laterally in all directions until such time that it thins-out or terminated by the edges of a basin in a depositional environment. Earth Science Relative Dating Page 4 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  Figure 8. Sedimentary Layers extending laterally separated by erosional surfaces ("Grand Canyon 1" by BigMikeSndTech is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/) D. Principle of Cross-cutting Relationship The principle of Cross-cutting Relationship is credited to James Hutton (1726—1797), which states that, an igneous intrusion (e.g. sills and dikes) that intersects through a layer of rock, is younger than the rock it cuts through. Another example is when a fault cuts through a sedimentary rock formation, the deposition of sedimentary rocks happened first followed by the faulting event. Older Younger Figure 9. Younger dike cutting through an older rock formation ("File: Intersecting Dikes in Black Canyon of the Gunnison.jpg" by Wing-Chi Poon is licensed under CC BY-SA 3.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/3.0) Earth Science Relative Dating Page 5 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  E. Principle of fossil succession Based on the observation made by William Smith (1769-1839), he noted that fossil content existed in a determinable order in rock layers. Consider this scenario, in an area, you observed that fossil A, B, and C succeed one another in a sedimentary layer from top to bottom. In another setting, you observed that a rock layer contains fossil A, and another one contains fossil B. By using the principle of fossil succession, you can infer from the observations made that the rock layer containing A is older. Figure 9. Relative Dating using fossil groups ©Lutgens and Tarbuck F. Inclusion The principle of Inclusion states that a rock fragment found inside another rock layer or formation (e.g. sandstone found inside a dike), is older than the rock containing it. Older Younger Figure 10. Inclusions found inside a rock formation ("Rock Inclusions" by Travis S. is licensed under CC BY-NC 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc/2.0/) Earth Science Relative Dating Page 6 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification. G. Unconformities Though not necessarily a part of the relative dating principles, unconformity principles are important concepts in understanding the events that occurred in the geologic past. In general, the term describes periods of nondeposition and/or erosion which can be observed between two rock layers. a. Disconformity This is characterized by an erosion surface that separates two rock layers of different ages, which are generally parallel with each other. In a cross-section, disconformities are usually shown by wavy lines. Disconformity Figure 11. Disconformity between the Erins Vale formation (bottom) and the Wilton Formation (top) ("Disconformity between the Erins Vale Formation (below) and the Wilton Formation (above)" by Dietmar Down Under is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/) b. Nonconformity When an igneous or metamorphic rock is overlain by sedimentary strata, this is called a nonconformity. Sedimentary Strata Dike Figure 12. Nonconformity between dike overlain by a sedimentary layer ("Non-conformity at Bombo Quarry" by Dietmar Down Under is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/) Earth Science Relative Dating Page 7 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  c. Angular unconformity This type of unconformity is represented by titled sedimentary layers overlain by horizontal sedimentary. Horizontal strata Angular unconformity Tilted strata Figure 13. Angular Unconformity between two nearly vertical strata ("Angular unconformity - Flagstaff Formation over Twist Gulch Formation (Salina Canyon, central Utah, USA) 67" by James St. John is licensed under CC BY 2.0/) How to use Relative Dating Principles Given a cross-section of rock layers, we use the relative dating techniques to sequence the strata from oldest to youngest. In the image below, each letter represents a rock layer/body. A,E, F are igneous rocks, while B, C, D, G, H, I, J, K are sedimentary rocks. Earth Science Relative Dating Page 8 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  Possible Sequence of rocks (top = youngest, bottom = oldest) Rock Layer/Body Reason/Relative Dating Technique C Law of Superposition G Law of Superposition E Principle of Cross-cutting Relationship, Inclusion D Law of Superposition I Law of Superposition A Principle of Cross-cutting Relationship F Principle of Cross-cutting Relationship J Law of Superposition K Law of Superposition H Law of Superposition B Law of Superposition Rock Layer/Body Reason/Relative Dating Technique C Law of Superposition G Law of Superposition E Principle of Cross-cutting Relationship, Inclusion D Law of Superposition I Law of Superposition A Principle of Cross-cutting Relationship F Principle of Cross-cutting Relationship B Law of Superposition H Law of Superposition K Law of Superposition J Law of Original Horizontality, Law of Superposition The main difference between the given answers is on the rock layers B, H, K, and J, these rocks appear to be folded therefore, their layers may have been overturned. Sample Questions and Answers that may be asked: 1.Why is rock J older than rock F? Using the principle of cross-cutting relationship, rock F cuts through rock J, which means that rock J is older. 2. Why are there two possible related ages for rock layers B, H, K, and J? The law of superposition only applies to undisturbed or undeformed rock layers, which means that J could be older or younger than B. 3. What unconformity can you observed between rock unit A and I? Since A can be inferred as an igneous intrusion, A & I display nonconformity. Earth Science Relative Dating Page 9 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  NAVIGATE SEQUENCE THE ROCK LAYERS (GRADED) Now it is your turn, using the principles of relative dating, arrange the rock units from oldest to youngest and answer the questions below. Answers may vary. (TOTAL: 15 points) Legend: Igneous - D, F Sedimentary - A, B, C, E, G, H, I, J Metamorphic - none ©Ludman and Marshak 1. (1 point) What type of unconformity is observable between H and I? 2. (1 point) What principle was used to determine the relative ages between rock unit B and C? 3. (1 point) What unconformity is observable between B and C? 4. (1 point) What principle can you use to determine the relative ages of D and F? 5. (1 point) What principle can you use to prove that B is younger than G? KNOT Summary: Relative dating uses principles and laws to determine the relative ages of rocks and other earth materials. It does not tell you the exact age (absolute age) but rather arranges the sequence of events that happened in the geologic time. Earth Science Relative Dating Page 10 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.  There are three principles credited to Nicolas Steno which are: a. superposition; b. original horizontality; and c. lateral continuity. James Hutton was credited for formulating the principle of cross-cutting relationship which simply states that the intruding rock is younger than the rock it intrudes. Other concepts involved are: law of fossil succession; inclusion; and unconformities (disconformity, unconformity, and angular unconformity. All of which are useful in determining and understanding the events that occurred in the geologic past. References Albarico, J.M. (2013). THINK Framework. Based on Ramos, E.G. and N. Apolinario (n.d.) Science LINKS. Quezon City: Rex Bookstore Inc Ludman, A., & Marshak, S. (2010). Laboratory Manual for Introductory Geology. New York City: W.W. Norton & Company, Inc. Lutgens, F. K., & Tarbuck, E. J. (2012). Essentials of Geology 11th Ed. New Jersey: Pearson Education, Inc. Wicander, R., & Monroe, J. S. (2010). Historical Geology: Evolution of Earth and Life Through Time, Sixth Edition. Belmont: Cengage Learning. Prepared by: Alan Royce B. Tizon Reviewed by: Bernard C. Llaguno Position: Special Science Teacher I Position: Special Science Teacher III Campus: Southern Mindanao Campus: Main Earth Science Relative Dating Page 11 of 11 © 2020 Philippine Science High School System. All rights reserved. This document may contain proprietary information and may only be released to third parties with approval of management. Document is uncontrolled unless otherwise marked; uncontrolled documents are not subject to update notification.