This means all living things have radioactive carbon in them. When an organism, eg a tree, dies it stops taking in carbon dioxide. The amount of carbon in the wood decreases with time as it decays into nitrogen with a half-life of about years. By comparing how much carbon there is in the dead organism with the amount in a living one, the age of the dead organism can be estimated.
The half-life of uranium is million years.
How Carbon-14 Dating Works
For example, in , two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain. Carbon is a radioactive isotope.
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- BBC Bitesize - GCSE Combined Science - Radioactive decay - AQA - Revision 3.
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It is found in the air in carbon dioxide molecules. The amount of carbon in the air has stayed the same for thousands of years. There is a small amount of radioactive carbon in all living organisms because it enters the food chain. Once an organism dies, it stops taking in carbon Prior Knowledge Students should: Be familiar with the rock cycle and the three types of rocks igneous, metamorphic, and sedimentary.
Understand the relative ages of layers from the law of superposition and what fossils are, but need not yet know exactly how the absolute ages of rock layers or fossils are determined. Have knowledge of the geologic time scale and the names of the eons throughout history.
Instructional Suggestions This lesson is intended to be completed in 1. Begin class with a brief introduction to the concept of radioactivity. If you do not have access to these, a class discussion, read aloud from an appropriate selection of text , or other video review would be appropriate. Be sure to define the following words with the class: Discuss the possible uses of radioactive material in science.
BBC Bitesize goes on to explain radioactive dating in the following section , though it is only text and images, without an interactive video. Introduce the MEA lesson concept: Your students' help has been requested by the Natural History Foundation in order to help them select the proper elemental isotopes to use in their radioactive dating process. The students must decide which elemental isotope is best suited for determining the absolute age of one of three ancient discoveries. Inform students that they will be completing a full essay written response with their decisions and reasoning at the end of this project.
Arrange students in groups of to prepare for the project it may be helpful to have predetermined groups ready. Allow students in each group to read the client letter. This image will help the students in their understanding of the client letter as well as developing their response essay.
Ask the students what they think of the information, and how would they determine which elemental isotope is the best for each item? Use their responses to transition into the next section. What is Radioactive Dating? Define and explain "radioactive dating" and "half-life. A half-life is a set amount of time after which half of the radioactive element will have disappeared because it turned into a new element! Radioactive dating is when scientists use the amount of radioactive materials in a rock or fossil and the half-life duration to calculate the absolute age of the rocks or fossils.
They can then complete calculations to see how many half-lives have passed, which will tell them the age of the rock! With your class, complete the following examples on the board: If a rock sample has g of radioactive material with a half-life of years, how much of the radioactive material will remain after years? What about after years?
Uses and hazards of radiation
A scientist finds a gram rock composed of grams of Lead and 50 grams of Uranium They know that the rock used to be entirely made of Uranium The half-life of U is million years. How old is the rock? After 1 half-life, how much Uranium will I have left?
What about after a second half life?
Emissions from fossil fuels may limit carbon dating - BBC News
Take how much Uranium we have left g and divide that by 2. Is that how much the scientist found in the rock? Yes And how many half-lives had to pass to get us to 50g? So, if each half-life is million years, and we did 2 of them, how old is our rock? If available, use manipulatives whenever they will be of assistance. Use the readiness questions to be sure each group understands the assignment. They must think of a rationale to explain why they would select a particular elemental isotope for each of the three items being dated.
You may discuss the readiness questions with the entire class, or go over them with each group separately. A teacher of advanced classes may be able to point the group to the questions and allow them to discuss only amongst each other, without direct instruction from the teacher.
Once the students understand what is requested of them, allow them to work in their groups. They should have a written explanation of the steps used to make this selection. The response letter must be written in paragraph form as a professional response to the client. This response letter is a full 5 paragraph essay: Students must have 1 written paragraph for each of the items to be dated. This paragraph must provide the rationale as to why the particular element was selected.
Collect all student work and wrap up: Ask students which choice they made and why they chose it. Open discussion with the entire class. What item do they think would be the oldest? Which one would be hardest to date? Block Day 2 min. Begin class with a review of Radioactive Dating and Half-Life. The BrainPop "Carbon Dating" video is a great review tool.
If you do not have access to this, a class discussion, read aloud from an appropriate selection of text , or other video review would be appropriate. Complete the BrainPop post-lesson quiz as a class. If you do not have access to this, a few review demonstrations using the blocks and some half-life calculations would be appropriate. Inform your students that you have heard back from the Natural History Foundation. They have more work for you!
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Arrange your students in the groups from the first section of this MEA. Once again, the group will have to complete a response letter indicating the elemental isotope they feel should be used on each of the new items. The new data only has 2 items, so students must complete a 4 paragraph response essay. Collect student essays and review responses as a class. The MEA has been completed. If using block scheduling, this allows you approximately 1 hour of the same class day to review concepts with the class, do reading on related topics, watch an educational video, or any other desired lesson reinforcement.
Supplemental Reading The BrainPop website has numerous information associated with the videos presented in the lesson plan. Advanced students may be able to learn from this information. Answering these questions should aid you in selecting an elemental isotope to be used in dating these objects: Ground sloth During what time eras or epochs do we think the giant ground sloth lived? About how many years ago was that?
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Stone slab from Antarctica What type of rock is the stone slab from Antarctica? In what eon were most of the rocks nearby this location formed? Petrified trees Although petrified trees used to be alive, what are they made of when we find them in the present day? In what era did most of the trees from the park in Arizona live?