AST 150: Radioactive Dating Game Activity

Transcription

1 Name AST 150: Radioactive Dating Game Activity Purpose: You will use the radioactive decay rate and original-daughter element ratios of carbon-14 and uranium-238 to determine the ages of different objects. Procedure: 1. Load PhET Radioactive Dating Game 2. Click on tab for Decay Rates 3. Select Carbon-14. Using the graph, the estimated half-life for C-14 is years. 4. Move the bucket slider all the way to the right. This will place 1000 C-14 atoms onto the screen. a. Click on the Start/Stop to stop the C-14 decay. Click on Reset All Nuclei b. Click on the Start/Stop to start the C-14 decay. Stop the decay as you get close to one halflife. c. Use the Step button to stop decay at one half-life. After 1 half-life, how many C-14 atoms of the 1000 original remain? d. Use the Start/Stop and Step buttons to reach two half-lives. After two half-lives, how many C-14 atoms remain? What fraction of C-14 atoms present at 1 half-life remain after 2 half-lives? e. Use the Start/Stop and Step buttons to reach three half-lives. After three half-lives, how many C-14 atoms remain? What fraction of C-14 atoms present at 2 half-life remain after 3 half-lives? f. Repeat Steps (a) to (e) with uranium-238. Start/Stop button Estimated half-life for U-238 is years. Bucket Slider Step button After 1 half-life, how many U-238 atoms of the 1000 original remain? What fraction of U-238 atoms present at 1 half-life remain after 2 half-lives? What fraction of U-238 atoms present at 2 half-life remain after 3 half-lives? g. Based on the results of 4a to 4f, explain the meaning of the word half-life in one sentence.

2 5. Click on the Measurement tab. 6. Under Probe Type, select Uranium-238 and Objects. Under Choose an Object, select Rock. 7. Click on Erupt Volcano. Let the simulation run until you reach 1 half-life. What % of the original uranium remains?. How many years did this take? 8. Under Probe Type, select Carbon-14 and Objects. Under Choose an Object, select Tree. 9. Click on Plant Tree. Let the simulation run until you reach 1 half-life. What % of the original carbon remains?. How many years did this take? 10. Explain why uranium-238 is used to measure the age of rocks while carbon-14 is used to measure the age of the tree trunk? 11. Click on Dating Game tab. There are objects on the surface and in the five layers beneath the surface. There are both rocks and fossils in each layer. 12. Select the Carbon-14 detector. Move the Geiger counter to each fossil and record the % of original in the table below 13. On the ½ life graph, move the green arrow right or left until the % of original matches the reading on the detector. Record your estimated age for each fossil in the table 14. Repeat Steps 12 and 13 using the Uranium2-38 detector to estimate the rock ages. For fossils with no remaining C-14 signal, use the rock ages to estimate fossil ages in the same layer. 15. Summarize how C-14 and U-238 dating together can be used to determine fossil ages.

3 Table: Radiometric Ages for Various Objects Object Measured using C-14 or U-238? % of Original Guessed Age Measured Age Animal Skull Living Tree Distant Living Tree House Dead Tree Bone Wooden Cup 1 st human skull 2 nd human skull Fish Bones Fish Fossil 1 Rock 1 Dinosaur Skull Rock 2 Trilobite Rock 3 Rock 4 Rock 5

4 AST 150 Activity: Solar System Properties Overview Purpose: To develop an understanding of the large-scale patterns which exist within the solar system. Materials: Graph paper, calculator, color pencils, planetary data. Procedure: Using the graph paper provided and the data tables that follow, create bar graphs to represent the following characteristics of the planets. Include Pluto and Eris on your graphs. Characteristics: Mass Radius Density Number of moons Inclination of orbit Eccentricity of orbit Sidereal Rotation Period Axis Tilt Analysis: Using your graphs as a guideline, group the planets based on similar traits. List your groups on a separate sheet of paper. You may have as many groups as you like, but each group must contain at least two planets. For each group, describe the characteristics which separate the planets in the group from those in other groups. Provide a statistical range for your parameters in each group. Questions: Answer on a separate sheet of paper: 1. Often, elementary school science classes learn that there are two types of planets gas giants and rocky planets. a. Are there any planets that don t seem to fit too well with either of these groups? b. Do the gas giants all fit together, or is a further division evident? 2. Are there some patterns that are the same for all, or nearly all of the planets, regardless of what group they re in? Describe any such patterns. 3. Are there any features of individual planets that stand out as being odd or out of place? If so, which features? 4. Consider the exoplanets we have studied so far, how many more categories would you need to add? diameter (Earth=1) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Eris

5 diameter (km) mass (Earth=1) mean distance from Sun (AU) orbital period (Earth years) orbital eccentricity mean orbital velocity (km/sec) rotation period (in Earth days) inclination of axis (degrees) inclination of orbit (degrees) mean temperature at surface (C) gravity at equator (Earth=1) escape velocity (km/sec) mean density (water=1) atmospheric composition number of moons 4,878 12,104 12,756 6, , ,000 51,118 49, * * *? ? to to to none CO 2 N 2 + O 2 CO 2 H 2 +He H 2 +He H 2 +He H 2 +He CH4 CH rings? no no no no yes yes yes yes no No

6 AST 150: Planet Quest Activity Visit the site Answer the following questions: 1. What is the current planet count? a. Candidates? b. Confirmed? Name: 2. What is the difference between a candidate planet versus a confirmed planet? (hint click the planet count) Click on the New Worlds Atlas link 3. How many stars have been found to have planets? 4. How many gas giants? 5. How many Hot Jupiters? 6. How many super earths? 7. How many terrestrial (earthlike) planets have been found? Start with the Planetquest Historic Timeline and Answer the following questions: 1. What year did Frank Drake predict extraterrestrial civilizations? 2. What year was the Hubble Space telescope launched? 3. What year was the first extrasolar planet discovered? 4. What was the first multiple planet system discovered? 5. When did the Spitzer space telescope first detect direct light from an exoplanet? Now select the Interstellar Trip planner Select three different journeys (destination/vehicle combos) and record your results: Now select the current news page Choose one current news story and write a one paragraph summary:

7 AST 150 Drake Equation Activity: Is There Life on Other Worlds? Goals To estimate the number of worlds in the Milky Way galaxy that have life To think about the size and composition of the galaxy and how that affects the possibility of extraterrestrial life To understand and estimate the terms of the Drake Equation Background Hundreds of new planets have been discovered orbiting other stars in the Milky Way galaxy and we have just begun to explore. Since there are many alien solar systems, the question of whether there is intelligent life living there becomes more prevalent. It raises many other questions as well. What is life? How does it begin and evolve on another planet? What conditions can life tolerate? How do we look for extraterrestrial life? Do you think there is intelligent life in our galaxy with which we can communicate? In 1961, Dr. Frank Drake identified eight terms to help people think about what would have to take place for such communication to be possible. where: and N = the number of civilizations in our galaxy with which communication might be possible; R * = the average rate of star formation per year in our galaxy f p = the fraction of those stars that have planets n e = the average number of planets that can potentially support life per star that has planets f l = the fraction of the above that actually go on to develop life at some point f i = the fraction of the above that actually go on to develop intelligent life f c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space L = the length of time such civilizations release detectable signals into space This is just one attempt to try and quantify the probability of extraterrestrial life. However, each of these factors has values that are open to interpretation. See what you think the chances are by making your own estimate for each of the terms below. The conservative and optimistic values indicate the range of opinion among scientists with regard to each term. You can use the conservative or optimistic estimates or use another value, depending on your own intuition. TERM 1 The total number of stars in the Milky Way galaxy BACKGROUND These numbers are based on observations of the stars in our galaxy, the Milky Way galaxy, and of other galaxies we believe to be like our own. Most scientists believe the number of stars to be 400 billion. Conservative estimate Optimistic estimate 100 billion 600 billion Your estimate

8 2 The percent of stars that are appropriate 3 The percent of these stars that have planetary systems 4 The average number of habitable planets or moons within a solar system 5 The percent of habitable planets or moons that develop life 6 The percent of planets with life that develop intelligent life 7 The percent of intelligent life that develops radio technology 8 The percent of current civilizations having radio technologies Many scientists believe that a star has to be like our sun, which is a Main Sequence, G- type star. Only about 5% of the stars in our galaxy are G- type stars, though about 10% are the closely related F- and K- type stars. About 50% of stars exist in binary or multiple systems, which many scientists feel make them inappropriate. Appropriate stars may not have planets circling them. We have only just begun detecting extra- solar planets, so we don t really know how common they are. Our only example of this term is our own solar system. Could Earth be the only habitable place in our solar system? Is our system typical? Remember that if one system has no habitable planets or moons and another has four, the average would be two per system. Having a planet or moon that is appropriate for life doesn t necessarily mean that life will arise. No real data are available to help us estimate this term. Earth is the only planet on which we know there is life. However, bacterial life existed on Earth shortly (geologically speaking) after its formation, possibly indicating that the development of life is easy. Many scientists believe that whether or not life arises depends on many factors. On Earth, humans developed intelligence, apparently as an evolutionary advantage. However, this term depends on how you define intelligence. Are dolphins, gorillas, octopus, and ants intelligent? Furthermore, single- celled life existed on Earth very early, and multicellular life took 2.5 billion years to form. Maybe the development of complex life, let alone intelligent life, is unusual. Communication with intelligent extraterrestrials requires that we hear from them. Given the vast distances of space, they would probably send signals which travel at the speed of light, such as radio waves. On Earth, humans have only just developed radio technology, so possibly this term should have a low value. But, we did eventually develop radio technology, so maybe this is true of all intelligent beings. Will an extraterrestrial s signals overlap with the lifespan of the receiving civilization? Extraterrestrials that sent signals a million years ago from a world a million light years away would still overlap with us, even if they died out long ago. So, how long do civilizations with radio technology last? A high level of technological development could bring with it conditions that ultimately threaten the species. Or maybe, once a society has radio technology, it may survive for a long time. Finally, radio signals may give way to more advanced, less noisy technologies such as optical fiber. No one would hear us! 5% 45% 5% % 0.1 On average, there is one habitable planet in every ten systems % Life is a rare accident that is unlikely to happen elsewhere % or less Only one in a million planets with life will develop intelligent life % or less Only one in a million planets with intelligent civilizations will develop radio technology % or less One in a million civilizations with radio tech will develop it in time to detect signals from another civilization 4 On average, there are four habitable planets in every system 100% Life will arise if conditions are appropriate 100% Any planet with life will develop intelligent life 100% All intelligent life will develop radio technology 10% One in a ten civilizations with radio technology will develop it in time to detect signals from another civilization Questions and Analysis 1. To find out your estimate of the number of worlds in the Milky Way galaxy that have intelligent life that we can detect using radio technology, fill out the Drake Equation worksheet and multiply the eight terms together. Write your answer here: 2. Based on your estimates, how good are our chances of hearing from intelligent extraterrestrials?

9 3. How does your answer to Question 2 compare to what you thought before you began the activity? 4. Can your answer to Question 1 be less than one? Why or why not? 5. When making estimates, in which terms did you have the most confidence? The least? Why? 6. Are you more optimistic or conservative when it comes to thinking about extraterrestrial life with radio technology in the Milky Way galaxy? Why? 7. How could you adjust the estimates in the equation to have it come out so that Earth is the only planet in the Milky Way galaxy with radio technology? 8. If tomorrow s newspaper headline read, Message Received from Outer Space what would it mean to you? 9. What would your reaction be if we discovered microbes on another planet? Plants? Insects? Mammals? Intelligent life? 10. If microbial life were discovered on another planet, what implications might such a discovery have?

10 11. How would you define extraterrestrial now? How does your current definition differ from the one that the class developed earlier in the activity? 12. What do you think is the most abundant life form on Earth? 13. If life exists elsewhere, what do you think it will look like?