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Transcript
M E T EVO S Y S L EAR H EARTH SYSTEM SCIENCE IN THE COMMUNITY ION UT T EARTHCOMM EarthComm ® EARTH SYSTEM SCIENCE IN THE COMMUNITY CHAPTER 1: THE SOLAR SYSTEM AND YOUR COMMUNITY FIELD TEST ™ Do not duplicate without the express permission of the American Geological Institute ©2000 American Geological Institute E 1 Earth System Evolution 3 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY ACKNOWLEDGEMENTS Principal Investigator Michael Smith is Director of Education at the American Geological Institute in Alexandria, Virginia. Dr. Smith worked as an exploration geologist and hydrogeologist. He began his earth science teaching career with Shady Side Academy in Pittsburgh, PA in 1988 and most recently directed Earth Science programs at the Charter School of Wilmington, DE. He earned a doctorate from the University of Pittsburgh’s Cognitive Studies in Education Program and joined the faculty of the University of Delaware School of Education in 1995. Dr. Smith received the Outstanding Earth Science Teacher Award for Pennsylvania from the National Association of Geoscience Teachers in 1991, served as Secretary of the National Earth Science Teachers Association, and serves on the review board of Science Education and The Journal of Research in Science Teaching. He worked on the Delaware Teacher Standards, Delaware Science Assessment, National Board of Teacher Certification, and AAAS Project 2061 Curriculum Evaluation programs. PRIMARY AND CONTRIBUTING AUTHORS Earth’s Dynamic Geosphere Daniel J. Bisaccio Soughegan High School, Amherst, NH Steve Carlson Middle School, OR Warren Fish Paul Revere Middle School Los Angeles, CA Miriam Fuhrman Carlsbad, CA Laurie Martin-Vermilyea American Geological Institute Alexandria,VA Mary-Russell Roberson Durham, NC Michael Smith American Geological Institute Earth’s Fluid Spheres Chet Bolay Cape Coral High School, Cape Coral, FL John Kemeny University of Arizona John Kounas Westwood High School, Sloan, IA Laurie Martin-Vermilyea American Geological Institute Alexandria,VA Mary Poulton University of Arizona,Tucson, AZ David Shah Deer Valley High School, Glendale, AZ Keith McKain Milford Senior High School, Milford, DE Peter Bryant Alfred Almond Central School, Almond, NY Janine Shigihara Shelley Junior High School, Shelley, ID Mary McMillan Niwot High School, Niwot, CO Steven Dutch University of Wisconsin Michael Smith American Geological Institute Steve Mattox Grand Valley State University, Allendale, MI Virginia Jones Bonneville High School, Idaho Falls, ID Earth System Evolution Bill Romey Orleans, MA Carl Laterza Division Avenue High School Levittown, NY Michael Smith American Geological Institute Tom Vandewater High School, Canton, NY Joseph Moran University of Wisconsin Laurie Martin-Vermilyea American Geological Institute Understanding Your Environment Geoffrey A. Briggs Batavia Senior High School, Batavia, NY Mary-Russell Roberson Durham, NC Julie Bartley University of West Georgia Ann Benbow Educational Visions, LaPlata, MD Lori Boronni-Engle,Taft High School San Antonio,TX Kathleen Cochrane Our Lady of Ransom School, Niles, IL Cathey Donald Auburn High School, AL Cathey Donald Auburn High School, Auburn, AL Bruce G. Smith Appleton North High School Appleton,WI Robert Gasataldo Colby College, Colby, Maine Richard Duschl Kings College, London, UK Michael Smith American Geological Institute Tim Lutz West Chester University,West Chester, PA Fran Hess Cooperstown High School Cooperstown, New York Earth’s Natural Resources Shannon Miller Llano Junior High School, Llano,TX Molly Miller Vanderbilt University Charles Savrda Auburn University Chuck Bell Deer Valley High School, Glendale, AZ Michael Smith American Geological Institute Rob Finley Austin,TX Content Reviewers Jay Hackett Colorado Springs, CO Lisa Barlow University of Colorado, Boulder, CO ©2000 American Geological Institute Earth System Evolution E 2 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Amanda Clarke Penn State Jill Slater General Atomics Whitman Cross Community College, Piedmont VA Bob Tilling United States Geological Survey Harold A. Geller George Mason University G. Richard Whittecar Old Dominion University Michelle Hall-Wallace University of Arizona Joseph Yahner Purdue University Leslie Hartten NOAA PILOT TEST REVIEWERS Lincoln Hollister Princeton University William Houston Michigan Technological University David G. Howell US. Geological Survey William Hoyt University of N. Colorado Christina Hulbe Oceans and Ice-NASA D.D. LaPointe Nevada Bureau of Mines and Geology Henrietta Lausten University of Colorado Brian Mapes NOAA Larry J. Rodgers Chaparral Middle School Diamond Barr, CA Linda Selvig Centennial High School Boise, ID Jane A. Skinner Farragut High School Knoxville,TN Daniel J. Bisaccio Souheyan High School, Amherst, NH Lynn E. Blair Karns High School, Knoxville,TN Paula Condra Knoxville,TN Sarah P. Damassa Lexington High School, Lexington, MA John Gallagher Port Angeles High School, Port Angeles,WA Fran Hess Cooperstown High School Cooperstown, New York Steve Mattox Grand Valley State University Paul A. Kirkpatrick Kamiak High School, Mulilteo,WA Katherine McCarville South Dakota School of Mines and Technology Robert Kitchen Portsmouth High School, Portsmouth, RI Dorothy Merrits Franklin and Marshall College Sandra K. Luedke Deer Valley High School, Glendale, AZ Bruce G. Smith Appleton North High School Appleton,WI Bernadette Tomaselli Lancaster High School Lancaster, NY Don Vincent Madison West High School Madison,WI Brian Vorwald Sayville High School Sayville, NY Jim Watson Soddy-Daisy High School Soddy-Daisy,TN Douglas Weisman Shorewood High School Shoreline,WA Kimberly L.Willoughby Southeast Raleigh High School Raleigh, NC PILOT TEST TEACHERS John Moore Burlington Institute of Technology Liz Nesbitt University of Washington Museum of Natural History Jeffrey Niemitz Dickinson College Richard C. Nolen-Hoeksema University of Michigan Judy Parrish University of Arizona Pat Pringle Washington Department of Natural Resources James Reichard Georgia Southern Perry Samson University of Michigan Eric Schuster Washington Department of Natural Resources John F. Madden Mountain View High School, Tucson, AZ Jean May-Brett Dominican High School, Kenner, LA Thomas McGuire Briarcliff High School, Briarcliff Manor, NY Hank B. Nash South Kitsap High School, Port Orchard,WA Tracy Poulson Oak Ridge High School, Oak Ridge,TN Conrad Rice The Charter School of Wilmington Wilmington, DE Alfred C. Robinson Appleton North High School Appleton,WI Rhonda Artho Dumas High School Dumas,TX Mary Jane Bell Lyons-Decatur Northeast Lyons, NE Rebecca Brewster Plant City High School Plant City, FL Terry Clifton Jackson High School Jackson, MI Virginia Cooter North Greene High School Greeneville,TN Monica Davis North Little Rock High School North Little Rock, AR Joseph Drahuschak Troxell Jr. High School, Allentown, PA Ron Fabick Brunswick High School Brunswick, OH Virginia Jones Bonneville High School Idaho Falls, ID ©2000 American Geological Institute E 3 Earth System Evolution 3 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Troy Lilly Snyder High School Snyder,TX Mary Cummane Perspectives Charter Chicago, IL Garry Sampson Wauwatosa West High School Tosa,WI Sherman Lundy Burlington High School Burlington, IA Mark Daniels Kettle Morraine High School Milwaukee,WI Alex Senger Wauwatosa West High School, Tosa,WI Norma Martof Fairmont Heights High School Capitol Heights, MD Beth Droughton Bloomfield High School Bloomfield, NJ Lynn Sironen North Kingstown High School North Kingstown, RI Keith McKain Milford Senior High School Milford, DE Rebecca Fredrickson Greendale High School Greendale,WI Karen Tiffany Watertown High School Watertown,WI Mary McMillan Niwot High School Niwot, CO Sally Ghilarducci Hamilton High School Milwaukee,WI Carmen Woodhall Canton South High School Canton, OH Kristin Michalski Mukwonago High Schhol Mukwonago,WI Kerin Goedert Lincoln High School Ypsilanti, MI San Jose Workshop Dianne Mollica Bishop Denis J. O’Connell High School Arlington,VA Martin Goldsmith Menominee Falls High School Menominee Falls,WI Arden Rauch Schenectady High School Schenectady, NY Laura Reysz Lawrence Central High School Indianapolis, IN Floyd Rogers Palatine High School Palatine, IL Ed Ruszczyk New Canaan High School New Canaan, CT Jane Skinner Farragut High School Knoxville,TN Shelley Snyder Mount Abraham High School Bristol,VT Joy Tanigawa El Rancho High School Pico Rivera,CA Dennis Wilcox Milwaukee School of Languages Milwaukee,WI Kim Willoughby SE Raleigh High School Raleigh, NC FIELD TEST TEACHERS Milwaukee Workshop Kerry Adams Alamosa High School Alamosa, CO Elke Christoffersen Poland Regional High School Poland, ME Randall Hall Arlington High School St. Paul, MN Patricia Jarzynski Watertown High School Watertown,WI Pam Kasprowicz Bartlett High School Bartlett, IL William Kean University of Wisconsin Milwaukee,WI Phlip Lacey East Liverpool High School East Liverpool, OH Christine Lightner Smethport Area High School Smethport, PA Jeffrey Messer Western High School, Parma, MI David Cardoza Branham High School San Jose, CA John Cary Malibu High School Malibu, CA Tom Clark Benicia High School Benicia, CA Jim Cunningham Sultana High School Hesperia, CA Kevin Kung Lowell High School San Francisco, CA Michael Laura Banning High School Wilmington, CA Ellen Metzger San Jose State University San Jose, CA George Moore Tennyson High School Hayward, CA Maggie Olson Benicia High School Benicia, CA Rick Nettesheim Waukesha South Waukesha,WI Ronald Ozuna Roosevelt High School Los Angeles, CA Randy Pelton Jackson High School Massillon, OH Reggie Pettitt Holderness High School Holderness, NH Tracy Posnanski University of Wisconsin Milwaukee,WI Wendy Saber Washington Park High School Racine,WI Phyllis Peck Fairfield High School Fairfield, CA Russ Reese Kalama High School Kalama,WA Gary Scott San Pedro Science & Tech. Center San Pedro, CA Richard Sedlock San Jose State University San Jose, CA ©2000 American Geological Institute Earth System Evolution E 4 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Todd Shattuck L.A. Center for Enriched Studies Los Angeles, CA Janet Ricker South Greene High School Greeneville,TN Heather Shedd Tennyson High School Hayward, CA Daniel Sauls Chuckey-Doak High School Afton,TN Tom Tyler Bishop O'Dowd High School Oakland, CA Jane Skinner Farragut High School Knoxville,TN Steve Whitmore McCloud High School McCloud, CA Sarah Smith Garringer High School Charlotte, NC Bridget Wyatt San Jose State University San Jose, CA Valerie Walter Freedom High School Bethlehem. PA Tennessee Workshop Christopher J. Akin Williams Milford Mill Academy Baltimore, MD Gregory Bailey Fulton High School Knoxville,TN Ted Koehn Lincoln East High Lincoln, NE Joan Lahm Scotus Central Catholic Columbus, NE Erica Larson Tipton Community, Tipton, IA Fawn LeMay Plattsmouth High Plattsmouth, NE James Matson Wichita West High Wichita, KS Dave Miller Parkview High Springfield, MO Nebraska Workshop John Niemoth Niobrara Public Niobrara, NE Sandra Bethel Greenfield High School Greenfield,TN Jason Ahlberg Lincoln High Lincoln, NE Don W. Byerly University of Tennessee Martin,TN Mary Jane Bell Lyons-Decatur Northeast Lyons, NE Virginia Cooter North Greene High School Greeneville,TN Rod Benson Helena High Helena, MT Michael A. Gibson University of Tennessee Martin,TN Julie Cook Jefferson City High School Jefferson City, MO Robert Hartshorn University of Tennessee Martin,TN Sharon D'Agosta Creighton Preparatory Omaha, NE Gilbert Highlander Red Bank High Scool Chattanooga,TN Steve Ferris Lincoln High Lincoln, NE Jim Hunt Chattanooga School of Arts & Sciences. Chattanooga,TN Bob Feurer North Bend Central Public North Bend, NE Thomas E. Jones University of Tennessee Martin,TN Sue Frack Lincoln Northeast High Lincoln, NE Mary Jane Kirkham Fulton High School Derek Geise University of Nebraska Lincoln, NE Bill Leonard Clemson University David C. Gosselin University of Nebraska Lincoln, NE Don Lewis Wendell Mohling National Science Teachers Association Theresa Harrison Wichita West High Wichita, KS Harold Pratt Barb Tewksbury Hamilton College Joy Hurst University of Nebraska Lincoln, NE Laure Wallace Nick Mason Normandy High School, St. Louis, MO Margaret Olsen Woodward Academy College Park, GA J. Preston Prather University of Tennessee Martin,TN June Rasmussen Brighton High School South Brighton,TN Paul Parra Omaha North High Omaha, NE D. Keith Patton West High Denver, CO Ed Robeck Hastings College Lincoln, NE Aaron Spurr Malcolm Price Laboratory Cedar Falls, IA Roseanne Williby Skutt Catholic High School Omaha, NE Caren Kershner Moffat Consolidated Moffat, CO ADVISORY BOARD Jane Crowder Arthur Eisenkraft Bedford (NY) Public Schools Tom Ervin Mary Kay Hemingway University ofTexas at Austin ILLUSTRATOR Stuart Armstrong GRAPHICS Eric Shih ©2000 American Geological Institute E 5 Earth System Evolution THE SOLAR SYSTEM AND YOUR COMMUNITY CHAPTER 1 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY TABLE OF CONTENTS THE SOLAR SYSTEM AND YOUR COMMUNITY E8 GETTING STARTED E8 SCENARIO E9 CHAPTER CHALLENGE E9 ASSESMENT CRITERIA E10 Activity One THE SCALE AND FORMATION OF THE SOLAR SYSTEM E11 ELECTROMAGNETIC RADIATION AND YOUR COMMUNITY E19 Activity Three SUNSPOTS AND SOLAR CYCLES E28 Activity Four ECCENTRICITY, CYCLES AND GLOBAL CLIMATE CHANGE E34 TIDES AND EARTH SYSTEM EVOLUTION E41 IMPACT EVENTS AND THE EARTH SYSTEM E49 Activity Two Activity Five Activity Six COMPLETING THE CHAPTER CHALLENGE E57 Field Test Published in 1999-2000 by It’s About Time, Inc. 84 Business Park Drive, Armonk, NY 10504 Phone (914) 273-2233 Fax (914) 273-2227 Toll Free (888) 698-TIME www.ITS-ABOUT-TIME.com Publisher Laurie Kreindler Editor Ruta Demery Design John Nordland Production Manager Barbara Zahm 2000 American Geological Institute E7 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY THE SOLAR SYSTEM AND YOUR COMMUNITY GETTING STARTED Earth is part of a solar system that has evolved over billions of years. You probably know a lot about our small corner of the universe. You have years of experience with life on the third planet from the sun. But suppose for a moment that our Earth was located in a different solar system. • • • • How far is the Earth from its sun? How big is the sun relative to the Earth? How many planets are there? How many moons, if any does the Earth have? What do you think? Write a paragraph about Earth in your imaginary solar system. Be sure to answer the questions above in your description. After you have finished describing your solar system, write a second paragraph. Describe what you think it would be like to live on that Earth, and how it would be different than being in our solar system. Be prepared to discuss your descriptions with your small group and the class. What would Earth be like if it was in another solar system? Earth System Evolution E8 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY SCENARIO Scientists recently announced that celestial object 1997XF, a 1 to 2 mile wide asteroid, would pass within 50,000 kilometers of Earth (one-eighth the distance between the Earth and moon) in October 2028. A day later, NASA scientists revised the estimate to 800,000 kilometers. News reports described how an iron asteroid had once blasted a hole more than 1 kilometer wide and 200 meters deep, and probably killed every living thing within 50 kilometers of impact. That collision, which formed Arizona’s spectacular Meteor Crater some 50,000 years ago, would wipe out a major city today. These reports have raised concern in your community about the possibility of a comet or asteroid hitting the Earth. Your class has been studying outer space. You see this concern as an opportunity to share some of the things you have learned with your fellow citizens. You decide to publish a brochure that will educate people about some of the possible hazards from outer space. However, your class has also decided to explain some of the benefits from living in our solar system. You want people who read your publication to better understand the vastness of our solar system, the time scales upon which it evolves, and how Earth is influenced by matter and energy in space. CHAPTER CHALLENGE In your publication, you will need to do the following: • • • Explain what comets and asteroids are, how they behave, how likely it is that one would collide with Earth in your lifetime, and what would happen if one did. Describe and explain the effects--both hazardous and beneficial--that solar radiation, sunspots, orbital eccentricity, and tides have on your community. Explain why extraterrestrial influences on your community are a natural part of Earth system evolution. Included with the brochure should be a model of the solar system that will help citizens understand the relative sizes of planets and the sun, and the relative distances between bodies in the solar system. 2000 American Geological Institute E9 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY ASSESSMENT CRITERIA Think about what you have been asked to do. Scan ahead through the chapter activities to see how they might help you to meet the challenge. Work with your classmates and your teachers to define the criteria for assessing your work. Record all this information. Make sure that you understand the criteria as well as you can. Earth System Evolution E 10 EARTHCOMM ACTIVITY ONE EARTH SYSTEM SCIENCE IN THE COMMUNITY THE SCALE AND FORMATION OF THE SOLAR SYSTEM Goals In this activity, you will: • Produce a scale model of the solar system. • Identify some limitations of scale models. • Calculate distances to objects in the solar system in Astronomical Units. • Explain in your own words the nebular theory of the formation of the solar system. Think About It Draw a picture in your notebook of the solar system. Without turning the pages of this book, try to draw the planets and the sun somewhat to scale. Also, try to make the distances from the sun to scale. Record your ideas in your notebook. Be prepared to discuss your responses with your small group and the class. The planets in this diagram are not drawn to scale. 2000 American Geological Institute E 11 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Investigate 1. Copy the table below into your notebook. To make a scale model of the solar system, try using the scale 150,000,000 km = 1 meter a) Divide all the distances in the first column by 150,000,000. Write your scaled down distances in your notebook, in meters. b) Divide all the diameters in the second column by 150,000,000. Write your scaled down diameters in your notebook, in millimeters. c) Looking at your numbers, what major drawback is there to using the scale 150,000,000 km = 1 meter? Table 1. Diameters of the sun and planets, and distances from the sun. Object Distance from Sun Diameter (kilometers) (kilometers) Sun 0 1,391,400 Mercury 58,000,000 4,878 Venus 108,000,000 12,104 Earth 150,000,000 12,756 Mars 228,000,000 6,787 Jupiter 780,000,000 142,800 Saturn 1,431,000,000 120,660 Uranus 2,877,000,000 50,800 Neptune 4,510,500,000 48,600 Pluto 5,916,000,000 3,100 2. Now try another scale--3,000,000 km = 1 meter. a) Divide all the distances in the first column by 3,000,000. Write your scaled down distances in your notebook, in meters. b) Divide all the diameters in the second column by 3,000,000. Write your scaled down diameters in your notebook, in millimeters. c) Looking at your numbers, what major drawback is there to using the scale 3,000,000 km = 1 meter? 3. Using what you have learned about scaling distances and diameters in the solar system, make a model of the solar system using paper, rulers, and tape measures. You may have to use different scales for the distances and the diameters. a) Explain the scale(s) you decided to use and your rationale for your choices. Earth System Evolution E 12 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY b) Is it possible to make a model of the solar system on your school campus in which both the distances between bodies and the diameters of the bodies are to the same scale? Why or why not? Reflecting on the Activity and the Challenge In this activity, you used ratios to make a scale model of the solar system. You found out that scale models help you appreciate the vastness of distances in the solar system. You also found out that there are some drawbacks to the use of scale models. Think about how you might use the model you made as part of your Chapter Challenge. Digging Deeper Words to Know Astronomical Unit (AU): A unit of measurement equal to the distance between Earth and the sun, or 150 million kilometers. Light-year: A unit of measurement equal to the distance light travels in one year, or 9.46x1012 kilometers. YOUR PLACE IN THE UNIVERSE Distances in the Universe Astronomers have to deal with very large distances. This would be cumbersome if they had to use units that we use to measure distances on Earth, such as kilometers. For example, the nearest star to Earth is Proxima Centauri. It is 40,678,000,000,000 kilometers away. It’s not so bad to write it, but just try to say it! Astronomers get around this problem by using big units. One unit is the Astronomical Unit (AU). One AU equals 150,000,000 km (93 million miles). This is the distance from the Earth to the sun. AU’s work well when talking about distances within the solar system. However, stars are so far away that AU's are too small a unit to be useful. For example, Proxima Centauri is 271,186 AU’s away, and it’s the closest star. For distances to stars, astronomers use units called light-years. A lightyear sounds like it would be a unit of time, because a year is a unit of time. However, a light-year is really a unit of distance. It is the distance that light travels in a year (9.46x1012 kilometers, or 9,460,000,000,000 kilometers). Light from Proxima Centauri takes 4.3 years to reach the Earth, so it is 4.3 light-years from us. 2000 American Geological Institute E 13 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Keyhole Nebula taken by the Hubble Space Telescope. Feb. 2000. Source: NASA Hubble Heritage. The Nebular Theory As you created a scale model of the solar system, you probably noticed how large the sun was in comparison to most of the planets. In fact, the sun contains over 99 per cent of all of the mass of the solar system. Where did all this mass come from? According to the current theory, a cloud of cosmic dust and gases began swirling around more than 4.6 billion years ago. The theory that the solar system began as a swirling cloud of dust is called the nebular theory. A nebula is an immense cloud of cosmic dust and gases. You can see the nebula in the winter constellation, Orion (see the photograph of Orion). A pair of binoculars would be helpful, especially if you live in or near a brightly-lit city. This nebula is very much like the one that formed our star, the sun. Stars are forming right now in the Orion Nebula and in nebulae all over our universe. Earth System Evolution E 14 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Words to Know Terrestrial planets: Rocky inner planets similar in size and composition to the Earth Gaseous planets: Outer planets made of icy gases. All but Pluto are much larger than the terrestrial planets. Orion is a prominent constellation in the night sky. Gravity causes the gases and dust in a nebula to begin to condense. At the same time, turbulence causes the gases to rotate. As they begin to swirl faster, the gases flatten out to resemble a disk, with most of the mass in the central core. Further contraction of this matter causes such intense gravitational forces and tremendous heat in the center (15 million degrees Celsius) that hydrogen atoms fuse to create helium in tremendous thermonuclear reactions. A star is born! This is how the sun was formed. Gravity also holds the star together even after fusion begins. This fusion reaction in the sun's interior causes great pressure, forcing energy far into space. This energy streams outward from the sun in all directions. From 150 million kilometers away, it streams to our Earth community to provide virtually all our energy. Just as the force of gravity holds the sun together while energy streams outward, some of the original swirling mass of the initial nebula is held in a plane around the sun by gravity. It formed the nine planets that make up the solar system, our place in space. The solar system consists of the Sun, the nine planets, sixty-seven (67) satellites of the planets, a large number of small bodies (the comets and asteroids), and the interplanetary medium. Four of these planets--Mercury, Venus, Earth, and Mars--are usually called terrestrial planets (earth-like). They are small and rocky. The larger planets--Jupiter, Saturn, Uranus, and Neptune--are more gaseous. Far from the sun, they are cold and much larger than the rocky planets. Pluto is the farthest planet from the sun. It is not like the terrestrial or the gaseous planets. If anything, it resembles the moons of the outer planets. Some scientists think it may not have been part of the original solar system, but captured later by the sun's gravity, or, a moon of an outer planet thrown into a unique tilted orbit around the sun. 2000 American Geological Institute E 15 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY The difference in size between the four inner terrestrial planets and the four outer gas giants in our solar system is clear when planet diameters are drawn to scale. Distance from the Sun is not scaled. Source: NASA Two diagrams are required to show the orbits of the planets to scale. Where is the Solar System? Have you ever seen the Milky Way? It is a light-colored band across the night sky. It is made of billions of stars, many of which are too small or too far away to be seen with the naked eye. The combined light from all these stars makes the band of light. The Milky Way is best seen away from city lights, on a night with no moon, in summer, fall, or winter. Earth System Evolution E 16 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY The Milky Way is not just a pretty sight in the night sky--it is our galaxy. A galaxy is a dense collection of stars. Galaxies are classified according to their shape--elliptical, spiral, or irregular. The Milky Way is a spiral galaxy. Our solar system is located on one of the arms of the spiral. When we look into the night sky and see a light-colored band, we are looking into the plane of the galaxy. The Milky Way is estimated to contain about 100-200 billion stars and is about 100,000 light-years across. Diagrams of the Milky Way Galaxy. Our solar system is located a spiral band about 2/3 of the way from the nucleus of the galaxy. Check Your Understanding 1. Define the distances “light-year” and “astronomical unit” in your own words. 2. Which of these units would you use to describe a) distances to various stars? b) distances to various planets within the solar system? c) widths of galaxies? Why? 3. In your own words, explain the nebular theory of the solar system. Write a short essay or make a poster with diagrams Applying What You Have Learned 1. Using the scale you used for distance in your model of the solar system, how far away would Proxima Centauri be from the Earth? 2. The moon is 384,000 km from Earth and has a diameter of 3,476 km. Calculate the diameter of the moon and its distance from the sun using the scale of the model developed in the "Investigate" section. 3. Refer again to Table 1. If a spaceship traveled at 100,000 km/hr, how long would it take to go from the Earth to a. the Moon? 2000 American Geological Institute E 17 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY b. Mars? c. Pluto? 4. What is the largest distance possible between any two objects in the solar system? 5. Using your understanding of a light year and the distances from the sun shown in Table 1, calculate how many minutes it takes for solar energy to reach each of the nine planets in the solar system (“light minutes”). 6. Write down your address the following ways. a. As you would normally address an envelope. b. To receive a letter from another country. c. To receive a letter from a friend from the center of our galaxy. Preparing for the Chapter Challenge Begin to develop your brochure for the chapter report. In your own words, explain your community’s position in the universe. Include a few paragraphs explaining what your scale model represents and how you chose the scale or scales you used. Inquiring Further 1. What if you wanted to make a scale model of the solar system in which you used the same scale for the diameters of the planets and the distances to the sun? Look at a map of your county and figure out where the outer planets would have to be located. 2. Make a “solar system walk” on your school grounds. Draw the objects to scale on the sidewalk in chalk. Pace off the distances between the sun and the nine planets. 3. Find out more about the process of nuclear fusion. Explain how and why energy is released as hydrogen atoms are converted into helium within the Sun. Be sure to include Albert Einstein’s famous equation, E=mc2 in your explanation. Earth System Evolution E 18 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY ACTIVITY TWO ELECTROMAGNETIC RADIATION AND YOUR COMMUNITY Goals In this activity, you will: • Use a spectroscope to explore how visible light is a mixture of colors. • Explain electromagnetic radiation and electromagnetic spectrum in terms of wavelength, speed, and energy. • Explain how electromagnetic radiation reveals the temperature of objects, such as stars. • Recognize the sun as the main external energy source for the Earth system. • Describe the flow of solar energy within the earth system in terms of reflection, scattering, and absorption. • Understand that some forms of electromagnetic radiation are essential and beneficial to life on earth, and others are harmful. Think About It Look at the spectrum as your teacher displays it on the overhead projector. Record in your notebook the colors in the order in which they appear. Draw a picture to accompany your notes. • What does a prism reveal about visible light? • The sun produces light energy that allows us to see. What other kinds of energy comes from the sun? Record your ideas in your notebook. Be prepared to discuss your responses with your small group and the class. A narrow beam of light creates a continuous spectrum of colors when passed through a prism. 2000 American Geological Institute E 19 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Investigate Part A – The Visible Spectrum 1. Follow the procedures below to make a spectroscope. a) Cover both ends of a cardboard tube with aluminum foil. b) Using scissors, make a thin (0.5 mm) slit in the foil at one end. c) Make a square opening in the foil at the other end about 1 cm by 1cm. d) Carefully cut a piece of diffraction grating into a 2 x 2-cm square. The diffraction grating is fragile and should only be handled by the edges. Use two small pieces of an overhead projector transparency to make a sandwich around the grating. e) Tape the 2 x 2-cm diffraction grating (or the sandwich of plastic and grating) over the 1-cm2 hole. 2. Hold the end with the diffraction grating to your eye. Direct it toward a source of reflected sunlight (CAUTION: Never look directly at the sun; doing so even briefly can damage your eyes permanently). Look for a spectrum along the side of the spectroscope. Rotate the spectroscope until you see the colors going from left to right rather than up and down. a) In your notebook, write down the order of the colors you observed. b) Move the spectroscope to the right and left. Record your observations 3. Look through the spectroscope at a fluorescent light. a) In your notebook, write down the order of the colors you observed. 4. Look through the spectroscope at an incandescent bulb. a) In your notebook, write down the order of the colors you observed. 5. How did the colors and the order of the colors differ between reflected sunlight, fluorescent light, and incandescent light? Describe any differences that you noticed. Earth System Evolution E 20 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Reflecting on the Activity and the Challenge The spectroscope helped you to see that visible light is made up of different color components. Visible light is only one of the components of radiation we receive from the sun. Solar radiation is one of the topics you will need to explain to your fellow citizens in your Chapter Challenge brochure. Digging Deeper Words to Know Electromagnetic radiation: Energy associated with electric and magnetic fields that transfer energy as they travel through space. In 1666, Isaac Newton found that he could split light into a spectrum of colors. As he passed a beam of sunlight through a glass prism, a spectrum of colors appeared from red to violet. Newton deduced that visible light was in fact a mixture of different kinds of light. About ten years later, Christiaan Huyygens proposed that light travels in tiny waves. The shorter the wavelength, the more it bends (refracts). Since violet light is refracted the most, it has the shortest wavelengths. This work marked the beginning of spectroscopy, the science of studying the properties of light. As you will learn, nearly 350 years of research in spectroscopy has answered many questions about matter, energy, time, and space. Electromagnetic radiation In the Investigate section, you made a spectroscope, an instrument that separates light into its various colors. Each color has a characteristic wavelength. These colors are called the visible spectrum. The visible spectrum is a small part of the entire spectrum of electromagnetic radiation given off by the sun. Electromagnetic radiation is associated with electric and magnetic fields that transfer energy as they travel through space. Electromagnetic radiation travels through space in the form of waves (like ripples that expand after you toss a stone into a pond). It travels at the speed of light (300,000 m/s). That’s eight laps around the earth in one second. Electromagnetic radiation has properties of both particles and waves. The colors of the visible spectrum are best described as waves. The light that produces an electric current in a solar cell is best described as a particle. 2000 American Geological Institute E 21 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY The diagram below summarizes the spectrum of energy that moves throughout the universe. Scientists divide the spectrum into regions by the length of the waves. Long radio waves have wavelengths from several centimeters to thousands of kilometers across, whereas gamma rays are shorter than the width of an atom (trillionth of a meter). Humans can only see wavelengths between 0.4 and 0.7 micrometers which is where the visible spectrum occurs (a micrometer is a millionth of a meter). This means that most of the electromagnetic radiation emitted by the sun is invisible to human eyes. However, you are probably familiar with some of the types of radiation besides visible light. For example, ultraviolet radiation gives you sunburn. Infrared radiation we detect as heat. The Electromagnetic spectrum. Wavelengths decrease from left to right. Energy increases from left to right. Learning from the Electromagnetic spectrum Humans have traveled to the moon and sent probes deeper into our solar system, but how do we learn about distant objects in our universe? We use a variety of instruments to collect electromagnetic radiation from them, with each tool designed for a specific part of the spectrum. Visible light tells us about the temperature of stars. Every object in the universe emits energy, but only the objects that are hot enough make visible light. The most abundant wavelength of light produced by any object, including the sun, is called the peak wavelength. Objects that are hot and are making visible light, usually look the color of their peak wavelength. People are not hot enough to emit visible light, but we do emit infrared light and can be detected using infrared cameras. The sun is yellowish because its peak wavelength is in the yellow region of the visible spectrum. Hotter objects produce their peaks toward the blue direction. Earth System Evolution E 22 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Very hot objects can have their peaks in the ultraviolet, x-ray, or even gamma. A gas under high pressure will radiate as well as a hot solid. Star colors thus reflect temperature. Reddish stars are a “cool” 3000 to 4000 degrees Kelvin (centigrade degrees above absolute zero, -273 degrees C). Bluish stars are hot (over 20,000 degrees Kelvin). Solar Energy in the Earth System The Sun is Earth’s main external energy source (radioactive heat and heat that remains from when the Earth first formed are the internal sources). Of all the incoming solar radiation, about half is absorbed by the Earth’s surface (see the diagram below). The rest of the solar radiation is either: • absorbed by the Earth’s atmosphere • reflected back into space by the Earth or clouds, or • scattered by the Earth’s atmosphere back into space. The solar energy budget. Molecules of dust and gas in the atmosphere interfere with some of the incoming radiation by changing its direction (but not its wavelength). This is called scattering. Scattering explains the colors we see in the sky. Our atmosphere scatters shorter visible wavelengths, such as blue, more readily than longer visible wavelengths. When the sun is low on the horizon, its light has to travel through more atmosphere than when it is directly overhead. By the time the light has completed its journey through the atmosphere, most of the shorter wavelengths of visible light have been scattered. The wavelengths that make it to your eyes unscattered are red and orange. 2000 American Geological Institute E 23 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Words to Know Albedo: the reflectivity of a surface, expressed as a percentage of light reflected. Energy budget: The amount of energy that flows into and away from the Earth. Of the solar radiation that is scattered, some is redirected out towards space. Other scattered radiation eventually makes it to the Earth’s surface. Scattered visible radiation is called diffused light. Diffused light makes it possible for you to see in a shaded area. Notice that the Earth’s surface absorbs more solar radiation than the atmosphere. That means that our air does not receive most of its warmth directly from the Sun. Instead, it receives its warmth from the Earth. The Earth’s surface absorbs solar radiation, then re-radiates it out as infrared heat. This is the heat you can feel rising from the beach sand on a hot sunny day. The atmosphere readily absorbs infrared heat. The reflectivity of a surface is referred to as albedo. Albedo is expressed as a percentage of radiation that is reflected. The albedo of the Earth, including its atmosphere, is about 30 percent. The albedo of particular surfaces on Earth varies. Thick clouds have albedo of about 80 percent, as does fresh fallen snow. The albedo of a dark soil is about 10 percent, so dark soil will often feel warm to the touch when the Sun is shining. Examples of the albedo of objects in the solar system are Venus (high albedo - our brightest planet) and our moon (which is rather low -- in fact it is surprising that it looks so bright when it is really a rather dark gray color with low albedo). Our Energy Budget The amount of energy received by the Earth is our energy budget. The energy budget changes from day to day, season to season and even on geologic time scales. Daily changes in radiant solar energy are the most familiar. It is usually cooler in the morning, warmer at mid-day, and it cools off at night. Visible light follows the same cycle, as our day moves from dawn to dusk and back to dawn again. But overall, the system is in balance. The Earth gains energy from the Sun, and loses heat energy to space. Earth is an open system with respect to energy. The amount of energy entering the Earth system is equal to the amount of energy flowing out. This flow of energy feeds all life on earth. It drives the weather; fuels the water cycle; powers our technology. All of Earth's systems depend on the input of energy from the Sun. Earth System Evolution E 24 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Harmful solar radiation Radiant energy from the sun warms the Earth (infrared) and provides light needed for photosynthesis. However, radiant energy from the Sun can be harmful. The ill effects of sunlight are caused by ultraviolet (UV) radiation, which causes sun-related skin damage. The ozone layer shields the earth from the sun's harmful UV rays. Ozone (O3, a molecule made up of three oxygen atoms) “screens” UV radiation in the upper atmosphere. Scientists have recently noted decreasing levels of ozone in the upper atmosphere. Less ozone means that more UV radiation reaches earth, increasing the danger of sun damage. The cause of the ozone depletion is under debate. Scientists agree that future levels of ozone will depend upon a combination of natural and man-made factors, including the phase-out of chlorofluorocarbons and other ozone-depleting chemicals. Check Your Understanding 1. What are the colors of the spectrum within visible light, from longest wavelength to shortest? 2. Which of the following has shorter wavelengths and greater energy: infrared or ultraviolet? Explain. 3. Use the concept of scattering of solar radiation to explain why the sky is blue or why a sunset is red. Applying What You Have Learned 1. Refer to the diagram of the solar energy budget in the Digging Deeper section of this activity to answer the following questions. For each question, make a new sketch of the solar energy budget. Answer in terms of both input and output. Remember that a change in one part of the system causes a decrease in other parts of the system. a) How would Earth's energy budget be affected if Earth's cloud cover were to double? b) What would be the effect of a decrease in the sun's energy output on Earth’s climate? Explain in terms of the energy budget. c) How would the earth’s solar energy budget be affected if a massive volcanic eruption put great amounts of fine dust and gases into the atmosphere. Again, answer in terms of input and output. 2. How does the EM radiation reaching the earth surface change due to Ozone (O3) depletion? 2000 American Geological Institute E 25 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY 3. What parts of the EM spectrum that come from the Sun does the atmosphere block? What gases are responsible for blocking each part of the EM spectrum? 4. What parts of the EM spectrum that go from the Earth into space does the atmosphere block? What gases are responsible for blocking each part of the EM spectrum? Preparing for the Chapter Challenge Recall that your challenge is to educate people about the hazards from outer space, and to explain some of the benefits from living in our solar system. Electromagnetic radiation has both beneficial and harmful effects on life on Earth. Use what you have learned in this activity to develop your brochure. 1. Make a list of some of the positive effects of the Sun’s energy on your community. Explain each item on the list. 2. Make a list of some of the negative effects of the Sun’s energy on your community. Explain each item on the list. Inquiring Further 1. Using radio waves to study distant objects. Radio waves from the Sun penetrate Earth’s atmosphere. Scientists collect these waves and study them. Do some research on how these waves are collected and what they tell us about the Sun and other celestial objects. 2. Technologies and the electromagnetic spectrum. Research some of the technologies based upon the travel of electromagnetic radiation. How do they work? How is electromagnetic radiation essential to their operation? What interferes with their operation? • microwave ovens • x-ray machines • television and radio transmission 3. History of Science. Find out more about Anders Jonas Angstrom (1814-1874), the Swedish physicist and astronomer. How did he contribute to study of spectroscopy? Why was a unit of measurement, the Angstrom (10-10 meters) named after him? 4. Luminosity and stellar distances. Suppose you had a group of 15-, 25, 40-, 60-, 75-, and 100-watt light bulbs at different distances in front of you on a dark night. How could you tell them apart? a) Investigate the relationship between brightness and distance. You will need a lamp or fixture, a light meter, masking tape, meter stick, and a collection of light bulbs (40-, 60-, 100-, and 150- Earth System Evolution E 26 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY watts), and a room that can be darkened. Design an investigation that will allow you to measure how the brightness of each bulb varies with distance. Describe how you will set up the investigation, what you will measure, and how you will make measurements. Make up a table to record your data. Write down your plan in your notebook. b) Graph brightness versus distance from the source for each bulb (wattage). Plot distance on the x-axis of the graph and brightness on the y-axis. Leave room on the graph so that you can extrapolate the data beyond the data you have collected. For example, your scale for distance might go from 0 meters to 10 meters. Plot the data for each bulb and connect the points with lines. Extrapolate the data by extending the lines on the graph using dashes. c) What is the general relationship between wattage and brightness (as measured by your light meter)? Explain. What is the general relationship between brightness and distance? Do all bulbs follow the same pattern? Why or why not? Draw a light horizontal line across your graph so that it crosses several of the lines you have graphed. Does a low wattage bulb ever have the same brightness as a high wattage bulb? Describe one or two such cases in your data. d) The easiest way to determine the absolute brightness of objects of different brightness and distance is to move all objects to the same distance. Investigate how astronomers handle this problem when trying to determine the brightness and distances to stars. Explain the meaning of the term “parsec”. 2000 American Geological Institute E 27 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY ACTIVITY THREE SUNSPOTS AND SOLAR CYCLES Goals In this activity, you will: • Graph recent sunspot activity. • Recognize the cyclic nature of sunspots. • Extrapolate sunspot activity for a given date in the future. • Understand that the Sun emits charged particles called solar wind. • Explain the effect of solar wind on people and communities. Think About It Violent solar eruptions, accompanying sunspots, produce enormous amounts of energy. • How might this change in the Sun's energy affect your Earth community? Record your ideas in your notebook. Be prepared to discuss your response with your small group and the class. Image of sunspots in soft x-ray Source: NASA Earth System Evolution E 28 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Investigate 1. Use the data in the table below to construct a graph of sunspots activity by year. a) Plot time on the horizontal axis and number of sunspots on the vertical axis. b) Connect the points you have plotted c) Look at your graph. Can you find a pattern in the sunspot activity? d) In your notebook, describe any pattern or cycle you observed. TABLE. SUNSPOT ACTIVITY 1899 TO 1998 Year 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 2000 American Geological Institute Sunspots 12.1 9.5 2.7 5.0 24.4 42.0 63.5 53.8 62.0 48.5 43.9 18.6 5.7 3.6 1.4 9.6 47.4 57.1 103.9 80.6 63.6 37.6 26.1 14.2 5.8 Year 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 Sunspots 16.7 44.3 63.9 69.0 77.8 64.9 35.7 21.2 11.1 5.7 8.7 36.1 79.7 114.4 109.6 88.8 67.8 47.5 30.6 16.3 9.6 33.2 92.6 151.6 136.3 Year 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 E 29 Sunspots 134.7 83.9 69.4 31.5 13.9 4.4 38.0 141.7 190.2 184.8 159.0 112.3 53.9 37.6 27.9 10.2 15.1 47.0 93.8 105.9 105.5 104.5 66.6 68.9 38.0 Year 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Sunspots 34.5 15.5 12.6 27.5 92.5 155.4 154.6 140.4 115.9 66.6 45.9 17.9 13.4 29.4 100.2 157.6 142.6 145.7 94.3 54.6 29.9 17.5 8.6 21.5 64.3 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Reflecting on the Activity and the Challenge In this activity you used the data table to plot the number of sunspots in a given year. You found out that the number of sunspots varies from year to year in a regular cycle. In your Chapter Challenge, you will need to explain sunspots, their cycles, and the effects of these cycles on your community. Digging Deeper SUNSPOTS As you noticed in the investigation, every 11 years the Sun undergoes a period of activity with many sunspots called the solar maximum. This is followed by a period of quiet or few sunspots called the solar minimum. During the solar maximum there are many sunspots and solar flares, both of which can affect communications and weather here on Earth. Sunspots are dark areas on the Sun. While sunspots are small compared to the size of the Sun, many of them are about the size of the Earth. A few have reached diameters of about 50,000 kilometers--about the size of Uranus and Neptune. They are formed when magnetic field lines just below the Sun's surface are twisted and poke though the solar photosphere. They are dark because they are about 1500 K cooler than the surrounding surface of the Sun. Sunspots are highly magnetic. It may be that the magnetism suppresses the circulation of heat in the region of the sunspot. This could account for their cooler temperatures. Sunspots last for a few hours to a few months. They appear to move across the surface of the Sun over a period of days; in fact, the sunspots are stationary and the Sun is rotating. As you saw in the Investigate section, the number of sunspots varies from year to year, and tends to peak in 11-year cycles. Sunspots occur in combination with other solar activity. The most spectacular of these are solar flares. During a solar flare, enormous quantities of ultraviolet, x-ray, and radio radiation are emitted. In addition, protons and electrons stream from flares at 800 km/hr. Earth System Evolution E 30 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Image of a solar flare taken from the final Skylab mission. June 1976. Source: NASA Words to Know Ionosphere: A layer of Earth’s atmosphere about 80 to 400 km above Earth's surface. These charged particles are called the solar wind. The particles in the solar wind excite gases in the Earth’s atmosphere, causing them to glow. This beautiful display of moving colors is called the Northern Lights, or aurora borealis, in the Northern Hemisphere. From the ground auroras appear as shimmering curtains of red and green light in the sky. In the southern hemisphere, they are called the Southern Lights, or aurora australis. The charged particles from a solar wind are attracted to the magnetic poles of the Earth. This makes it easier for people who live near the equator to see an aurora than those who live near the equator. The stream of charged particles from solar wind can disrupt radio signals by disturbing the ionized layers of our atmosphere. The sounds of your favorite radio station or the signals sent by a ham radio operator travel as electromagnetic radiation (radio waves). Radio signals travel around the earth by bouncing off the ionosphere, a layer of the atmosphere 80 to 400 km above Earth’s surface. The ionosphere forms because incoming solar radiation blasts electrons out of the gases, leaving a mix of electrons and charged atoms, or ions. The ionosphere acts like a mirror, reflecting portions of the radio waves back to earth. This allows radio signals to travel around the globe. Storms on the Sun (solar flares) intensify the solar wind, which makes the ionosphere thicken and strengthen. When this happens, radio signals from Earth, as well as radio signals coming to Earth (remember that electromagnetic radiation from objects in space include radio waves), get trapped inside the ionosphere and cause a lot of interference. Thus, solar flares can disrupt or even black out long-distance transmission of radio waves on Earth. However, solar activity is less of a problem for long distance communication today than in the past since most communication is via satellites. 2000 American Geological Institute E 31 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Some scientists believe that sunspot cycles affect weather on Earth--that during times of high sunspot activity, our climate is warmer, and during times of no or low sunspot activity, our climate is colder. However, considerable debate still exists about this idea. Check Your Understanding 1. How do solar flares interfere with long-distance communication? 2. In your own words, explain what is meant by the term “solar wind.” Applying What You Have Learned 1. Study the graph that you made showing sunspot activity. You have already determined that sunspot activity occurs in cycles. Using graph paper, construct a new graph that would predict a continuation of the cycle from 2000 to 2015. 2. How would a sunspot maximum affect Earth's energy budget? 3. Looking at the Sunspot Activity Data Table, predict what you think the weather might have been like in your community in 1963 - 1968. Use local resources to examine the average high and low temperatures for each month in those years. Compare the data to data from last year. Do you see any differences between then and last year? 4. The next sunspot maximum is predicted to be 2001. Using the data from your Sunspot Activity Data Table, predict the next sunspot minimum. 5. Make a list of the possible consequences of solar flares to the following members of your community: an air traffic controller, a radio station manager, the captain of a ship at sea. Can you think of other members of your community that would be affected by solar activity? 6. Radio signals travel to Earth from distant portions of the galaxy. Which would be a better time to study incoming radio signals – during solar minimum or during solar maximum? Explain your answer. Earth System Evolution E 32 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Preparing for the Chapter Challenge You have been asked to help people in your community to understand how events from outside the Earth affect their daily lives. Look back through this activity and think about how you can use the following questions to prepare your report. 1. How have sunspots affected your community in the past? 2. How might sunspots affect your community in the future? 3. What are some of the benefits from sunspots? 4. What are some of the problems caused by sunspots? 5. If your community is at a latitude close enough to the pole to see aurora, explain how they are caused. Inquiring Further 1. Viewing sunspots. If you have a telescope, you can view sunspots by projecting an image of the Sun onto white cardboard. Never look directly at the Sun, with or without a telescope. Stand with your back to the Sun, and set up a telescope so that the large end is pointing toward the Sun and the other end is pointing toward a piece of white cardboard. You should see a projection of the Sun on the cardboard, including sunspots. If you map the positions of the sunspots daily, you should be able to observe the rotation of the Sun over a couple of weeks. 2. Aurora. Have people in your community ever seen Northern Lights? Even if your community is not very far north, do some research to see if the Northern Lights have ever extended to your community. At times, a very active solar wind produces spectacular Northern Lights displays as far south as Texas. 3. Technology. Sunspot maximums increase the dosage of radiation that astronauts and people in airplanes receive. Do some research on how much radiation astronauts receive during sunspot minimums and maximums. How about airplane passengers? How do the amounts compare to the solar radiation we receive at the Earth’s surface? How do scientists balance safety with the issue of the extra weight that would be added to aircraft, spacecraft or spacesuits to provide protection? 4. History of Science. Investigate the British physicist Edward Victor Appleton who was awarded the Nobel Prize in physics in 1947 for his work on the ionosphere. Other important figures in the discovery of the properties of the upper atmosphere include • Oliver Heaviside • Arthur Edwin Kennelly 2000 American Geological Institute E 33 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY ACTIVITY FOUR ECCENTRICITY, CYCLES AND GLOBAL CLIMATE CHANGE Goals In this activity, you will: • Measure the major axis and focal distance of an ellipse. • Calculate the eccentricity of Earth's orbit. • Understand the relationship between the focal distance and eccentricity of an ellipse. • Draw Earth's changing position in relation to the Sun. • Explain how natural cycles of the Earth’s rotation and orbit around the Sun may cause changes in climate. Think About It Draw a picture of the Earth’s orbit around the Sun. What shape is the orbit you have drawn? How might the shape of the Earth’s orbit around the Sun affect climate? Record your ideas in your notebook. Be prepared to discuss your responses with your small group and the class. Earth as seen from the Moon. Photo taken by Apollo 11 crew, NASA, July 1969. Earth System Evolution E 34 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Investigate 1. Fold a piece of paper in half and use a straightedge to draw a horizontal line across the width of the paper along the fold. Put two dots 10 cm apart on the line toward the center of the line. Label the left dot “A,” and the right dot “B.” 2. Tape the sheet of paper to a piece of cardboard and put two pushpins into points A and B. 3. Put the string over these two pins and pull the loop tight using the pencil point as shown in the photograph. The procedure for drawing an ellipse. 4. Draw an ellipse with the pencil, keeping the string pulled tight with the pencil point. 5. Draw a small circle around either A or B and label it “sun.” 6. Repeat the process using the following measurements and labels: • Two points 8 cm apart labeled C and D (1 cm inside of points A and B) • Two points 6 cm apart, labeled E and F (2 cm inside of points A and B) • Two points 4 cm apart, labeled G and H (3 cm inside points A and B) • Two points 2 cm apart, labeled I and J (4 cm inside points A and B) 2000 American Geological Institute E 35 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY 7. Copy the data table shown on the next page into your notebook. a) Measure the width (in centimeters) of ellipse “AB” at its widest point. This is the major axis “L”. (see photograph below). Record this in your data table. b) Record the length of the major axis for each ellipse in your data table. c) Record the focal length “d” (distance between the two pushpins) for each ellipse in your data table (see photograph). d) Calculate the “eccentricity” of each ellipse by dividing the focal distance by the length of the major axis. This is represented by the equation E = d/L, where d is the focal distance and L is the length of the major axis. Record the eccentricity of each ellipse in your data table. Ellipse Major Axis (L) (cm) Focal Length(d) (cm) Eccentricity E=d/L AB CD EF GH IJ Ellipse AB showing focal length “d” and major axis length “L”. Earth System Evolution E 36 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY 8. Study your data table to find a relationship between the focal distance and the eccentricity of an ellipse. a) Record the relationship between focal distance and eccentricity in your notebook. b) Looking at your ellipses as orbits, does the distance to the center of the Sun stay the same in any orbit? c) Which orbit has the least variation in distance (eccentricity) from the sun throughout its orbit? Which has the most? 9. Earth’s orbit has an eccentricity of about 0.017. Compare this value to the ellipse with the lowest eccentricity of those you drew. Why does it make sense to describe Earth’s orbit as “nearly circular”? Reflecting on the Activity and the Challenge In this activity, you explored a geometric figure called an ellipse. You also learned how to characterize ellipses by their eccentricity. The orbits of all nine planets in our solar system are ellipses, with the Sun at one focus. As you will see, although the Earth’s orbit is very nearly circular (only slightly eccentric), the shape of its orbit may play a role in climate change. Digging Deeper Eccentricity As you saw in the Investigate section, the shape of ellipses can vary from nearly circular to quite flattened. The more flattened the ellipse is, the more “eccentricity” it has. Values of eccentricity range from zero (perfect circle) to nearly 1.0. Most planets in the solar system have slightly elliptical orbits. The Earth does not take a perfectly circular path around the Sun. Instead, the Earth’s orbit is an ellipse. Earth’s orbit has an eccentricity of 0.017 (a value much lower than the eccentricity of ellipse IJ from the investigation, which looked much like a circle). If you were to draw an ellipse with an eccentricity of 0.017 on a large sheet of paper, most people would call it a circle. However, the eccentricity of Earth’s orbit is enough to make the Earth’s distance from the Sun vary between 153,000,000 kilometers and 147,000,000 kilometers. To make things more complicated, the Earth’s orbit experiences changes in eccentricity over time. The Earth's orbit shifts from nearly circular (about 0 eccentricity) to more elliptical (about 0.05 eccentricity) as it is tugged by the gravity of the Sun and the other planets. This happens on a cycle of about 100,000 years. 2000 American Geological Institute E 37 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY In 1930, a Yugoslavian scientist named Milutin Milankovitch predicted that changes in the eccentricity of the Earth’s orbit influenced glacial cycles. Two other periodic cycles figure into his hypothesis: changes in the amount that the Earth’s axis is tilted and changes in the way the Earth wobbles on its axis. Earth’s axis is now tilted at an angle of 23.5 degrees. On a cycle lasting about 41,000 years, its axial tilt varies from 22.1 degrees to 24.5 degrees. The greater the tilt angle, the greater the difference in temperature between summer and winter. Earth also has a slight wobble (like a spinning top that is winding down). The wobble is caused by differences in the gravitational pull of the Moon and Sun on the Earth. It takes about 23,000 years for this wobble to complete a cycle. As it wobbles, the timing of the seasons changes. As you know, winter occurs when a hemisphere is pointed away from the sun. Right now, winter occurs between December and March in the Northern Hemisphere. Winter also now occurs when the Earth is closest to the Sun (remember that Earth has a slightly elliptical orbit, so Earth is not always the same distance from the Sun). Winters and summers are now both relatively mild in the Northern Hemisphere. The closer distance to the Sun in northern winter balances out the fact that the axis is tilted away form the Sun. But about 11,500 years from now, Earth’s spin axis will be half-way through this wobble cycle. Winter will occur from June to November in the Northern Hemisphere, and when the Earth is farthest from the Sun. Thus, winters and summers will be more extreme in the Northern Hemisphere. In this way, the wobble of the Earth’s axial spin can cause a change in climate. During these changes, the total amount of solar radiation received by the Earth remains relatively constant. However, certain places receive different amounts of solar radiation during different times of year than usual. Milankovitch hypothesized that these three cycles coincide about every 100,000 years. When this happens, the amount of solar radiation received in the northern part of the Northern Hemisphere (about 65 degrees North) is reduced during the summertime. Snow that has fallen in the winter and accumulated on the land in North America, Northern Europe, Scandinavia, and Asia doesn’t melt as much as usual in the summer, and glaciers begin to develop. (Ice expansion doesn’t begin in the Southern Hemisphere because there is less land there to provide a surface for glaciers.) Once glaciers begin to grow, their high albedo (reflectivity) reflects more of the Sun’s radiation back to space. This contributes to worldwide cooling. The more it cools, the less snow melts in summer, and glaciers continue to expand. This is called a positive feedback mechanism in earth systems science. Because the Earth has become completely iced over, something must stop this positive feedback process. Earth System Evolution E 38 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Over the years, the Milankovitch hypothesis has alternately fallen in and out of favor with other scientists. Recent evidence from deep-sea sediments seems to indicate a good correspondence between climate changes and the three cycles Milankovitch tied to global climate. However, the debate continues. Check Your Understanding 1. In your own words, explain what is meant by the eccentricity of an ellipse. 2. For an ellipse with a major axis of 25 cm, which one is more eccentric, the one with a focal distance of 15 cm or with a focal distance of 20 cm? Explain. Applying What You Have Learned 1. The major axis of the Earth's orbit is 298,000,000 km, and the focal distance is 4,800,000. Calculate the eccentricity of Earth’s orbit. 2. On the GH line you created for your “Investigate” activity, draw the Earth at its closest position to the Sun and the farthest position away from the Sun. 3. Refer to the table below that shows the eccentricities of the planets. a. Which planet would show the greatest percentage variation in distance from the Sun during the year? b. Which planet would show the least percentage variation in distance from the Sun throughout the year? Explain. c. Describe any relationship between distance from the Sun and the eccentricity of a planet’s orbit. d. Why might Neptune farther away from the sun at times than Pluto is? Eccentricities of the Planets Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto 2000 American Geological Institute Eccentricity 0.206 0.007 0.017 0.093 0.048 0.054 0.047 0.009 0.249 E 39 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY 4. Draw a scale model to show changes in the Earth’s orbit over a cycle of 100,000 years. a. Draw the orbit of the Earth with a perfectly circular orbit at 150,000,000 km from the Sun. Use a scale of 1 cm = 20,000,000 km. Make sure that your pencil is sharp, and draw the thinnest line possible. b. Make another drawing of the maximum ellipse of the Earth's orbit. This ellipse has 153,000,000 km as the furthest distance and 147,000,000 as the closest point to the Sun. c. Does the difference in distance from the Sun look significant enough to cause a lot of temperature difference? Explain. 5. Look at your diagram of ellipses from the investigation. Put a dot on the line in the middle between points A and B (5 cm inside of either point). Put the point of a drawing compass on the center dot. Extend the compass along the horizontal line so that the pencil touches the ellipse. Draw of a circle of this radius. Preparing for the Chapter Challenge 1. In your own words, explain the Milankovitch theory of glacial cycles. 2. If his theory is correct, what effect has eccentricity had on your community in the past? What effect might it have in the future? Inquiring Further Eccentricity outside the solar system. The number of stars identified as having orbiting planets is growing all the time. Investigate the orbits of planets around other stars. Earth System Evolution E 40 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY ACTIVITY FIVE TIDES AND EARTH SYSTEM EVOLUTION Goals In this activity, you will: • Graph the length of a year on Earth over time. • Understand the role of the Moon and the Sun in creating tides. • Understand the role of tides in slowing the rotation of Earth. • Extrapolate the future rate of decrease in rotation period of Earth given present data. • Explain the influence of tides on your community. Think About It Look at the photograph below. It shows a bay at low tide. • What makes water rise and fall to create tides? • How often do tides rise and fall? Explain your answer? Record your ideas in your notebook. Be prepared to discuss your responses with your small group and the class. A winter extreme low tide along the Chesapeake Bay, Maryland. Photo by Mary Hollinger, NOAA 1998. 2000 American Geological Institute E 41 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Investigate The table below represents data that paleontologists have gathered about the effect of tides on the number of days in a year over time. 1. Copy the data table into your notebook. Change in Rotation of Earth Due to Tidal Forces Period Date Length of Year Cambrian 500 million years 415 days Devonian 400 million years 405 days Carboniferous 300 million years 395 days Triassic 200 million years 385 days Cretaceous 100 million years 375 days Today present 365.25 days 2. Plot this data on graph paper. Label the x-axis “Number of Days in a Year” and the y-axis “Years Before Present.” 3. Give your graph a title. a) Determine the rate of decrease in the number of days per 100 million years (calculate the slope of the line). b) How many fewer days are there every 10 million years? c) How many fewer days every million years? d) Determine the rate of decrease per year. e) Do you think changes in the length of a year reflect changes in the time it takes the Earth to orbit the Sun, or changes in the amount of time it takes Earth to rotate on its axis? In other words, is a year getting shorter, or are days getting longer? How would you test your idea? Reflecting on the Activity and the Challenge In this activity you observed that tides decrease the number of days in a year over time. That’s because tides slow the rotation of the Earth, making each day longer. Explaining how tides slow the rotation of the Earth, and how this has affected the Earth are tasks for the Chapter Challenge. Earth System Evolution E 42 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Digging Deeper THE INFLUENCE OF TIDES ON YOUR COMMUNITY When the Earth was first formed, a day was only about 6 hours long. Over time, Earth days have been getting longer and longer. In other words, the Earth rotates fewer times during each revolution around the Sun. The result is that there are fewer and fewer days in a year, as you saw in the Investigate section. Why is the Earth rotation slowing down? It has to do with the Moon and tides. The Moon exerts a gravitational pull on the Earth. This pull actually stretches the Earth, but only by about 20 centimeters (the bulge of water in the diagram is greatly exaggerated). However, the Moon’s gravity affects the Earth’s oceans to a much greater degree, since water moves more freely than land. Oceans actually bulge significantly toward the Moon. On the exact opposite side of the Earth, the oceans also bulge away from the Moon. This bulge is due to centrifugal force, the “fleeing force” that keeps water in a bucket when the bucket is swung in a circle on a rope. The Moon’s gravity acts like a rope that makes water ”flee” or bulge on the opposite side of the Earth. These bulges create high tides (see Figure on next page). As the Earth rotates every 24 hours, a shoreline experiences two high tides--one when the shoreline is nearest the Moon, and one when the shoreline is on the opposite side of the Earth from the Moon. The tidal cycle is not exactly 24 hours. Even though the Earth rotates exactly once in 24 hours, by the time it has done so, the Moon is in a slightly different place because it has traveled along its orbit around the Earth. That’s why the Moon rises 50 minutes later each night, and why high tides are about 50 minutes later each day. Since there are two high tides each day, each subsequent tide is about 25 minutes later than the previous one. 2000 American Geological Institute E 43 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Schematic diagram of tides. Shorelines away from the poles experience two high tides and two low tides per day. Adapted from Tarbuck and Lutgens. The gravitational pull of the Sun also affects tides. However, since the Sun is so much farther away than the Moon, it doesn’t affect the tides as much as the Moon. The Moon is only 386,400 km away from the Earth, while the Sun is 150,000,000 kilometers away. The Moon exerts 2.4 times more force on the Earth than the Sun. The changing positions of the Sun and the Moon relative to each other and the Earth cause variations in high and low tides. Earth System Evolution E 44 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY When the Sun and the Moon are both on the same side of the Earth, pulling together, high tides are even higher than usual. (When the Earth, Moon and Sun has this alignment, it is called a new moon.) On the side of the Earth near the Sun and Moon, oceans are pulled more strongly than usual, and bulge toward the Sun and Moon. On the opposite side of the Earth, oceans are pulled less strongly than usual, and thus bulge away from the Sun and Moon. These higher-than-usual tides are called spring tides. A spring tide also occurs during a full moon, when the Sun and the Moon are on opposite sides of the Earth When the Sun and Moon are at right angles to one another, their pulls cancel each other somewhat, and high tides are lower than usual. These tides are called neap tides. They occur during quarter moons. 2000 American Geological Institute E 45 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Low tide in the Bay of Fundy as seen in Selma, Nova Scotia, Canada Photos by John Shane, North Doxbury, VT. 1998. High tide in the Bay of Fundy. Even during any given high tide, the height of tides varies worldwide depending on the size and shape of the body of water. High tide is greatest in enclosed basins where the tidal waters are concentrated into narrowing bays. A good example of this is the Bay of Fundy, where tidal ranges are as great as 15 meters (nearly 50 feet). Most shorelines have much less tidal range, usually less than one meter (2-3 feet). The fact that the oceans are constantly responding to the pull of the Moon slows the rotation of the Earth. In effect, the oceans are lagging behind the Earth, and the friction of this lag gradually slows the Earth’s rotation. That’s why the length of a day (one rotation) has gradually become longer and longer over geologic time. As the Earth system evolves, cycles change as well. Earth System Evolution E 46 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Check Your Understanding 1. What effect have tides had on the length of a day? Explain. 2. What effect have tides had on the length of a year? 3. Draw a picture of the positions of the Earth, Moon and Sun for a spring tide. Applying What You Have Learned 1. Study your graph. At the current rate, how long will it take the Earth to slow its rotation so that one axis rotation (day) is the same as its revolution (year)? 2. a) How many low and high tides will there be per year when there is one Earth rotation per orbital revolution? b) What do you think will be the duration of each high and low tide? 3. Refer to the diagram below and the schematic diagram of tides shown in the investigate section of this activity. At what latitudes would the three types of tides form? Include a diagram and an explanation. • Semidiurnal: two high tides and two low tides each day, both about the same height • Mixed: two high tides and two low tides each day, but one high tide is higher than the other • Diurnal: one high tide and one low tide each day. 4. Search the Internet to find tide tables for the ocean shoreline that is nearest to your community. Try < http://www.co-ops.nos.noaa.gov/tp4days.html>. a. When is the next high tide going to occur? Find a calendar to determine the phase of the Moon. Figure out how to combine these two pieces of information to determine whether this next high tide is the bulge towards the moon or away from the moon. b. The tide tables also provide the predicted height of the tides. Look down the table to see if the how much variation there is in the tide 2000 American Geological Institute E 47 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY • • • heights. Recalling that the Sun also exerts tidal force on the ocean water, try to draw a picture of the positions of the Earth, Moon and Sun for: The highest high tide you see on the tidal chart. The lowest high tide you see on the tidal chart. The lowest low tide you see on the tidal chart. Preparing for the Chapter Challenge To complete the chapter challenge, it is necessary to understand how the Moon and Sun affect the Earth. This activity allowed you to explore the effects of the Moon and Sun on the length of the day and on tides. Write several paragraphs explaining the many ways that tides affect a community, and how the changing length of the day may affect the earth system. Be sure to support your positions with evidence. Inquiring Further 1. Tides and Power Generation. The natural flow of water into and out of a tidal basin can be harnessed to generate electricity. Investigate how electricity is generated from tides and write a paper to explain it. 2. Tidal changes. When there is one Earth rotation per orbital revolution, Earth will face the Sun for half of the present day year and away from the Sun for the other half. How would this affect all systems of our Earth community? Make a list of all the possible changes to climate, oceans, and energy and life systems. Use some of these changes to write a diary entry from the point of view of someone who lives with half a year of light and half a year of darkness. 3. Tides and the Biosphere. There are many plants and animals that have evolved to live in the intertidal zone. Investigate how these fewer tidal cycles will affect those organisms? Earth System Evolution E 48 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY ACTIVITY SIX IMPACT EVENTS AND THE EARTH SYSTEM Goals In this activity, you will: • Calculate the energy (in joules) released when an asteroid collides with Earth. • Compare natural and man-made disasters to the impact of an asteroid. • Make scale drawings of an asteroid impact. • Understand the consequences to your community should such an impact occur. Assess the potential of the risk of an asteroid or comet collision. Think About It Meteor Crater (shown on next page) in Arizona is one of the best preserved meteor craters on Earth. It is 1.25 km across and about 4 km in circumference. 1. How large (diameter) do you think the meteor was that formed Meteor Crater? a. 25 meters b. 250 meters c. 750 meters d. 1,250 meters 2. Write down several ideas about how the impact of the meteor would have affected living things near the crater. Record your ideas in your notebook. Be prepared to discuss your responses with your small group and the class. 2000 American Geological Institute E 49 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Meteor Crater, Arizona. The crater is 1.25 kilometers across. Source: http://www.barringercrater.com/science/ Investigate Given the following information, calculate the amount of energy released when an asteroid collides with Earth: • The spherical, iron-nickel asteroid has a density of 8 g/cm3. • It is 2 km in diameter. • It has a velocity of 30 km/sec relative to the Earth. Note: It is very important to keep track of your units during these calculations. You will be expressing energy with a unit called a “joule.” A joule is [(kg)(m2)]/s2. 1. To find the volume use the formula Volume of a sphere =4/3 Πr3 a) Show all work and include all units. b) Convert your answer to cubic meters. Earth System Evolution E 50 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY 2. Multiply the volume by the density to find the total mass, as follows: a) First, convert 8 g/cm3 into kg/m3. If you don’t know how to do this, see the conversion figure below. It shows how to multiply a number and its unit by various ratios that each equal 1. You choose ratios that allow you to cancel out units that appear in both the numerator and the denominator until you have left the units that you want--in this case kg/m3. After you’ve multiplied everything out, if you have a number greater than 1 on the bottom, divide it into the top number so that your final answer is in the form of some number of kilograms per 1 cubic meter. b) Next, multiply volume (in m3) by density (in kg/m3) to arrive at mass (in kg). c) Show all work and include all units. How to convert 8 g/cm3 to kg/m3 100 cm =1 m 1 kg = 1000 g 1 kg 8g X (cm)(cm)(cm) 100 cm X 1000 g 100 cm X 1m 100 cm X 1m 1m 3. Since the asteroid is moving, we will use the formula for kinetic energy, as follows: kinetic energy = 1/2(mass)(velocity2) a) First, convert the given velocity of 30 km/s into m/s. b) Now calculate kinetic energy using the formula given above. Your units should be [(kg)(m2)]/s2. One of these units equals a joule. 4. Use the table below to compare this amount of energy to known phenomena. a) In your notebook, explain how the energy of this hypothetical asteroid impact compares to some other known phenomena. Phenomena Annual output of the Sun Severe earthquake 100 megaton H bomb Atomic bomb 2000 American Geological Institute Kinetic Energy 1034 joules 1018 joules 1017 joules 1013 joules E 51 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY 5. Suppose you wanted to make a scale drawing or model of this hypothetical asteroid and Earth. The diameter of the Earth is 12,756 km. The diameter of the asteroid is 2 km. If you made the diameter of the asteroid 1 mm, what would the diameter of the Earth be? How about if you made the diameter of the asteroid 0.5 mm, which is probably about as small as you can draw. Then what would the diameter of the Earth be? Reflecting on the Activity and the Challenge You have calculated the energy released when an asteroid two kilometers wide hits the Earth and you have compared it to other explosive events. This comparison will be helpful in writing up your Chapter Challenge brochure. Digging Deeper ASTEROIDS AND COMETS Asteroids Asteroids are rocky bodies, smaller than planets. Most orbit the Sun in the space between Jupiter and Mars called the Asteroid Belt. There are at least 50,000 asteroids. The largest is about 1,000 km in diameter, and the smallest ones are the size of grains of sand. Some of the asteroids have very eccentric orbits that cross the Earth’s orbit. Of these, perhaps a few dozen are 1 kilometer or larger in diameter. These are the ones astronomers worry about. Image of the Asteroid Ida. Image taken by the Galileo Orbiter, NASA/JPL, 1994. Earth System Evolution E 52 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY In 1989, an asteroid almost 1 km in diameter crossed Earth’s orbit just 6 hours before Earth passed the same point. The asteroid was traveling at 70,000 km per hour. At its closest point to Earth, it was only about as far away as twice the distance to the moon. Astronomers calculated that if it had hit Earth, it could have produced a crater 1 km in diameter and 2 km deep. According the number of impact craters that have been found and dated on Earth, astronomers think asteroids of this size hit the Earth every few hundred million years. Many (but not all) scientists believe that the extinction of the dinosaurs 65 million years ago was caused by the impact of an asteroid or comet 10 km in diameter. Such a large impact would have sent up enough dust to cloud the entire Earth’s atmosphere for many months. This would have blocked out sunlight and killed off many plants, and eventually, the animals that fed on those plants. Not only did the dinosaurs die out; 5075 percent of all plants and animals also became extinct. Among the evidence supporting this hypothesis is a 1-cm layer of iridium sediment about 65 million years old that can be found worldwide. Iridium is rare on Earth, but common in asteroids. NASA is currently forming plans to discover and monitor asteroids that are at least 1 km in size and cross the Earth's orbit. The experts think the threat from asteroids is to be taken very seriously and that a plan must be developed to avoid an impact. Comets Comets are like large dirty snowballs. They contain frozen gases, cosmic dust and small rocky particles. Many comets orbit the Sun. Their orbits are usually very eccentric and large, carrying them out past Pluto. Comets are usually a few kilometers in diameter, but they appear much bigger as they get closer to the sun. That’s because the Sun’s heat vaporizes the frozen gases of a comet, and the vapor surrounding the comet makes it look larger. Some comets have tails, which stream away from the Sun. Radiation pressure and solar wind (charged particles) from the Sun push dust and gases away from the comet, producing the tail. Probably the most well-known comet is Halley's Comet, which rounds the Sun about every 76 years. Its appearance was first documented in 240 BC. More recently, it has passed by Earth in 1910 and 1986. 2000 American Geological Institute E 53 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Photo of Halley’s Comet, which appeared in the night sky in 1986. Source: NASA Meteoroids, Meteors, and Meteorites Meteoroids are tiny particles in space, such as leftover dust from a comet’s tail or fragments of asteroids. Meteoroids are called meteors when they enter Earth's atmosphere, and meteorites when they strike the Earth (see photograph). About 1000 tons of material is added to the Earth each year by meteorites, much of it through dust-sized particles that float down through the atmosphere. There are several types of meteorites. About 80 percent that hit Earth are stony in nature and are difficult to tell apart from earth rocks. About 15 percent are iron-nickel. The rest are either a mixture of iron-nickel and stony or are made of a very different material. These are called chondrites and may represent material that was never part of a larger body like a moon, planet or asteroid. They are probably original solar system materials. Photo of a Martian meteorite. Source: NASA/AMES 1996. Earth System Evolution E 54 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY Check Your Understanding 1. What is the Asteroid Belt? 2. If the asteroid that passed near the Earth in 1989 was traveling at 70,000 km/hour, how does that compare to the speed of the hypothetical asteroid in the “Investigate” section? Which was going faster? Applying What You Have Learned 1. If an asteroid or comet were on a collision course for Earth, what factors would determine how dangerous the collision might be for your community? 2. How would an asteroid on a collision course endanger our Earth community? 3. Comets are largely composed of ice and mineral grains. Assume a density of 1.1 grams/cm3). How would the energy released in a comet impact compare to the asteroid impact you calculated in the Investigate section? (Assume the comet has the same diameter and velocity as the asteroid.) 4. Based on your answer above, are comets dangerous if they impact the earth? 5. Based on the information in the Digging Deeper section, how likely do you think it is that an asteroid with a diameter of 1 km or greater will hit the Earth in your lifetime? Explain your reasoning. 6. Add the asteroid belt to the model of the solar system you made in the first activity. You will need to think about how best to represent the vast number of asteroids and their wide range of sizes. 2000 American Geological Institute E 55 Earth System Evolution EARTHCOMM THE SOLAR SYSTEM AND YOUR COMMUNITY Preparing for the Chapter Challenge Assume that scientists learn several months before impact that an asteroid will hit near your community. Assume that you live 200 miles from the impact site. What plans can your family make to survive this disaster? Work with your group to make a survival plan. Present your group's plan to the entire class. Be sure to record suggestions made by other groups. This information will prove useful in completing the Chapter Challenge. Inquiring Further 1. Here’s an experiment to simulate an asteroid or comet hitting the Earth. Fill a shoebox partway with plaster of Paris. When the plaster is almost dry, drop two rocks of different sizes into it from the same height. Carefully retrieve the rocks and drop them again, this time from higher distance. Let the plaster fully harden, then examine and measure the craters. Which is biggest? Which is deepest? Did the results surprise you? 2. Do some research on the current thinking among astronomers about how to prevent impacts from large comets or asteroids. 3. Research the Barringer Crater (Meteor Crater). The crater has been named for Daniel Moreau Barringer, yet he did not discover the crater. Explain how he came to understand how craters form. Earth System Evolution E 56 EARTHCOMM EARTH SYSTEM SCIENCE IN THE COMMUNITY COMPLETING THE CHAPTER CHALLENGE In this chapter, you and your group investigated how matter and energy from outside our planet influence the Earth system. You made scale models to discover the vastness of our solar system and learned how scientists work with special units of measurement when exploring space beyond our Sun and its nine planets. You used a spectroscope to investigate visible light, and learned that it is but a small part of the range of energy that travels through space within the electromagnetic spectrum. You learned about the global energy budget, how the Earth system depends upon the flow of energy from outside the planet, and that some electromagnetic radiation can be harmful to life on Earth. By graphing sunspot activity over the last 100 years, you began to explore cycles within the Earth system. These cycles include changes in the flow of energy from the Sun, changes in the Earth’s axial tilt, orbit and rotation, and changes in the movement of tides. You also learned that cycles operate over many different time scales, ranging form daily cycles (tides) to cycles that last a decade or so (sun spots) to many thousands of years (eccentricity, wobble of the Earth’s axis, and axial tilt). You learned that when some of these cycles line up, global changes can result (ices ages). You also investigated how over time, Earth has been affected by matter such as comets, asteroids, and meteorites. You are now ready to use your understanding of the uniqueness of Earth’s position within the Solar System, Galaxy, and Universe to finalize your chapter report. Using the work you produced throughout the chapter, prepare your report about the proposed developments for your community. The report should inform the public about: • • • What comets and asteroids are, how they behave, how likely it is that one would collide with Earth in your lifetime, and what would happen if one did. Describe and explain the effects--both hazardous and beneficial--that solar radiation, sunspots, orbital eccentricity, and tides have on your community. Explain why extraterrestrial influences on your community are a natural part of Earth system evolution. Review and discuss the grading criteria that were agreed upon by the class at the beginning of the chapter, If you plan to submit your report as a group, remember that each group member must contribute fairly to the final product. 2000 American Geological Institute E 57 Earth System Evolution
