Read It! Station Directions Each member of the group will read the passage and answer the questions from the task cards on the lab sheet in the Read It! section. It is important to remember that the answers will come directly from the reading passage.
How Old Is It? How do scientists know the ages of rocks? Geologic age dating assigning an age to materials is an entire discipline of its own. In a way this field, called geochronology, is some of the purest detective work earth scientists do. There are two basic approaches to discovering the age of rocks: relative age dating, and absolute age dating. To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This is called the Rule of Superposition. You may not know the exact age, but you can tell if one rock layer is older relative to another layer. Absolute age dating gives age in actual years. It s based either on fossils which are recognized to represent a period of time, or on radioactive decay of specific isotopes. Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times. After all, a dinosaur wouldn t be caught dead next to a trilobite. The narrower a range of time that an animal lived, the better it is as an index of a specific time. No bones about it, fossils are important age markers. But the most accurate forms of absolute age dating are radiometric methods. Absolute age dating method works because some unstable (radioactive) isotopes of some elements decay at a known rate into daughter products. This rate of decay is called a half-life. Half-life simply means the amount of time it takes for half of a remaining isotope to decay to a daughter product. So, geochronologists just measure the ratio of the remaining parent atom to the amount of daughter, and they determine how long the molecule has been hanging out decaying. Not all rocks have radioactive elements. Sedimentary rocks are notoriously radioactive-free zones. So, to date those, geologists look for layers like volcanic ash that might be sandwiched between the sedimentary layers, and that tend to have radioactive elements. Each radioactive isotope works best for applications. The half-life of carbon 14, for example, is 5,730 years. On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years. So, carbon 14 is used to date materials that aren t that old geologically, say in the tens of thousands of years, while potassium-argon dating can be used to determine the ages of much older materials, in the millions and billions year range. Geologists tend to mix and match relative and absolute age dates to piece together a geologic history. If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well. Like the other kind of dating, geologic dating isn t always simple.
What two methods are used for determining the age of rocks and fossils? A. Relative and Absolute Dating B. Absolute and Resolute Dating C. Carbon and Water Dating D. Relative and Absent Dating Which is true about relative dating? A. Relative dating uses the half-life of isotopes to get the exact age of a rock or mineral B. Carbon-14 dating is used on rocks and minerals that are relatively young C. Potassium Argon dating is used on very old rocks and minerals. D. The law of superposition is used to determine a rocks relative age. What is half-life? A. The length and organism lived in prehistoric times. B. The time it takes for the radioactivity of a specific isotope to fall to half its original value C. Half the life of an organism D. The time it takes for a geologist to determine the age of a rock or mineral Which type of absolute dating method would be best for a rock layer believed to be millions of years old? A. Carbon-14 B. Potassium-Argon C. Chlorine dating D. Isotope 51
Watch It! Station Directions Each member of the group will go to the website listed on task card #1 Complete the task cards in order. Every student will answer the questions from the task cards on the lab sheet in the Watch It! section of the lab sheet.
YouTube https://goo.gl/qpfamm Cloud https://goo.gl/mskfpt URL is case-sensitive 1. Click Play on the video. 2. Answer questions from cards #2-4 on your lab sheet. What is the law of superposition? YouTube What is the law of crosscutting? What is the law of inclusions?
Research It! Station Directions Each member of the group will go to the website listed on task card #1 Complete the task cards in order. Every student will answer the questions from the task cards on the lab sheet in the Research It! section.
You are looking at a clock that represents the entire history of Earth. 1. Go to http://deeptime.info/ 2. Answer the questions on your lab sheet. 1. Click on each of the different eons and write a one sentence summary of what was happening during that eon on your lab sheet. 1. When do scientists believe the first life form showed up on Earth? Hint: use the categories on the left hand side. 2. About what time was it on Earth s geologic scale when dinosaurs showed up? 1. When did the first Homo sapiens (early humans) show up? 2. When do scientists believe the moon was formed? 3. What is the most surprising to you when looking at the geologic time of Earth?
Explore It! Station Directions One member of the group will read the task cards in order. The group will be responsible for completing each of the tasks that are being read. Each member of the group will then write their conclusions down on the lab sheet in the Explore It! section.
Use the outcrop models for this station. Each model represents an outcrop of the Earth s crust from a different part of the world. 1. Which layer is the oldest layer? 2. Which layer is the youngest or newest? 3. How do you know? The Law of Superposition states that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom. Each layer is younger than the one beneath it and older than the one above it. Index fossils are useful for dating and correlating the strata in which it is found. When the same fossils are found in all of the same strata (layers) across different regions of the Earth, then the rock layers and fossils are likely the same age. 1. Which fossils would make good index fossils from the models? Hint: You will have to turn them. 1. Which are not good index fossils in the model? Why? 2. Which fossils are the oldest? 3. Which fossils are the youngest?
Illustrate It! Station Directions Each member of the group will draw a quick sketch on the lab sheet that shows they understand the concept that is being taught. Use the colored pencils and markers that are provided. The directions for the sketch are provided on the task card at the table.
Illustrate It! Station Directions Draw three images to help explain the laws of relative rock dating. The three laws are: 1. The law of superposition 2. The law of crosscutting 3. The law of inclusions
Organize It! Station Directions It is recommended that you have completed at least two of the following stations before working at this station. -Read It! -Explore It! -Watch It! -Research It! Create 4 columns of cards using the card with the border as the category. Once complete have your teacher sign your lab sheet. Please mix up the cards again before the next group arrives at this station.
Write It! Station Directions It is recommended that you have completed at least two of the following stations before working at this station. -Read It! -Explore It! -Watch It! -Research It! Answer each of the task card questions on the lab sheet in complete sentences.
How do geologists use index fossils to determine the age of rock strata? What is the difference between relative dating and absolute dating? Briefly describe the geologic time scale.
Assess It! Station Directions It is recommended that you have completed at least two of the following stations before working at this station. -Read It! -Explore It! -Watch It! -Research It! Each member will answer the questions from the task cards on the lab sheet in the Assess It! section.
Which fossil would make the best index fossil? A. Beetle B. Flower C. Frog D. Fish Outcrop #1 Outcrop #2 If a student used the analogy of her stacking books in her locker, which law of relative dating is she referring to? A. Law of Superposition B. Law of Crosscutting C. Law of Inclusions D. Law of Inertia Which statement is incorrect about the Geologic Time Scale? A. It is believed that the moon was created very soon after the Earth was created. B. Prokaryotes showed up on Earth long before reptiles and small plants. C. Modern humans have only been on Earth for a tiny fraction of Earth s existence. D. Dinosaurs showed up just after the Earth was created. Which era best represents when humans first appeared on Earth? A. Cenozoic C. Archean B. Mesozoic D. Hadean
Geologic Time Scale Explore It! Task Card #1 1. 2. 3. Name Task Card #3 1. Task Card #4 1. 2. 3. Write It! Task Card #1: Task Card #2: Task Card #3:
Geologic Time Scale Illustrate It! Assess It! #1 #3 #2 #4 Name Research It! Task Card #2: Hadean Archean Proterozoic Paleozoic Mesozoic Cenozoic Organize It! Read It! #1 #3 Task Card #3: 1. 2. Task Card #4: 1. 2. 3. #2 #4
Geologic Time Scale Name Watch It! Task Card #2: Task Card #3: Task Card #4: