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Center #2: Absolute vs. Relative Age Dating
Directions: Read the Introduction to answer the questions that follow. Then complete the step-by-step activity that follows.
Part I Read the Introduction:
Scientists use radiometric dating to find out the absolute age of an object or rock. They are able to do this because radioactive isotopes emit or let off nuclear particles at a regular rate during radioactive decay. This original radioactive isotope is called the parent. Over time as the parent isotope lets off particles it changes to another element called the daughter. Each isotope does this at a regular but different rate. By looking at the amount of parent isotope and daughter element in an object or rock the age can be calculated. During radioactive decay, radioactive isotopes break down into stable isotopes of other elements. These radioactive isotopes have half-lifes; this is the amount of time it takes from one-half of the original amount to decay.
Scientists can also use relative-age dating to gain a clearer understanding of geologic events in Earth’s history. It does not allow scientists to determine exactly how many years ago an event occurred, but it can be somewhat helpful when studying geologic time. Relative-age dating gives an approximate age of rocks, fossils, and events using uniformitarianism, original horizontality, superposition, cross-cutting relationships, and the principle of inclusion. Rock layers and the fossils that reside within them tell stories about their age and experiences
Part II Answer the Questions
Directions:Refer to the passage and p. 595-597 and p. 601-603 in your textbook to answer the questions below.
1. Compare and contrast absolute-age dating and relative-age dating below:
2. How does radiometric dating determine the exact age of rocks and fossils? ______
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3. Describe half-life: ______
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4. Define isotope: ______
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5. Examine the rock layers in the picture above.
- List the rock layers in order of age (by letter)
- Identify what a scientist might find in these rock layers that would help determine their age.
- Explain which relative-age dating technique scientists would use to determine the approximate age of these rock layers.
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Part III Create a Scientific Model of Radioactive Decay
Directions:In this activity you will make a scientific model of radioactive decay. Attempt to complete the activity BEFORE you ask for help.
Parent Isotope = White Beans
Daughter Element = Red-Brown Beans
1. Place 12 white beans in bowl. This represents the parent isotope which has just formed. Draw a picture of what the bowl looks like below:
2. Draw a circle graph showing how much of the material is made up of parent isotope and daughter element:
3. Remove six of the white beans in the bowl and replace them with six red-brown beans. This represents what a material would be made up of after one-half life. Draw a picture of what the bowl looks like below:
4. Draw a circle graph showing how much of the material is made up of parent isotope and daughter element.
5. Remove three of the white beans in the bowl and replace them with three red-brown beans. This represents what a material would be made up of after two half-lifes. Draw a picture of what the bowl looks like below:
6. Draw a circle graph showing how much of the material is made up of parent isotope and daughter element:
7. After three half-lifes how many white and red-brown beans would be in the bowl? Draw a picture to show what you think the bowl would look like below:
8. Draw a circle graph showing how much of the material is made up of parent isotope and daughter element after three half-lifes:
Part IV: Analysis and Communication of Results
Directions: Use the space below to create a line graph of radioactive decay based on what you observed in part III of this activity. Determine the independent variable (x axis), dependent variable (y axis), a title, and if your graph requires a key.