Education ProductNational Aeronautics and          Teachers   Grades 4–12Space Administration                           a ...
a Teacher’s Guide                                                       with activities                                   ...
my notes                                                    The following people contributedG. Jeffrey Taylor             ...
Table of ContentsAbout This Book                                                                         iiiAbout the Luna...
About this BookThese materials have been designed for use                      The length of time needed to complete anin ...
About the                                  Lunar Sample DiskLegacy of Apollo                                    How to Sch...
About the Slide SetThe Collection                                               How to Obtain a CopyA set of thirty-six 35...
Activity MatrixScience Process Skills Unit 1   Distance to the Moon          Diameter of the Moon Pre- Apollo   Reaping Ro...
Activity MatrixScience Standards Unit 1      Distance to the Moon             Diameter of the Moon Pre- Apollo      Reapin...
Activity MatrixMathematics Standards  Unit 1   Distance to the Moon           Diameter of the Moon  Pre-  Apollo   Reaping...
Teacher’s Guide      THE MOON                                         GATEWAY TO THE SOLAR SYSTEM                         ...
and falling rain have erased much of Earth history,         scopes were invented. Although we now know theyespecially the ...
points about the impact process. For ex-ample, objects impacting at a variety ofvelocities (hence kinetic energies) produc...
Maria mysteries                                                                                              Some mysterie...
regolith. Be forewarned that the regolithsamples in the Lunar Sample Disk arelabeled “soil.” Although it is everywhere,the...
One of the great potential bits of information                                    MOON ROCKSstored in the complex pile ato...
Highland rocks, the lunar magma                    Hawaii developed a method to determine the iron    ocean, and maybe a c...
bombarded with exceptional intensity during that                                      potassium (chemical symbol K), rare-...
Experiments conducted on                                                                               mare basalts and py...
meteorites are collectively called SNC meteorites. If                                    mometers set up by the Apollo mis...
Moon forming together, a two-body                                                                                         ...
and all, never to be seen again. Yes, this sounds                                  was at least 500 km deep. The first mine...
Almost as soon as the crust had formed, perhaps        110 million years ago. This, therefore, is the age ofwhile it was s...
THE MOON AND EARTH:                                        extinctions are not understood. One possibility is thatINEXORAB...
The Curatorial Facil-                                                                                                     ...
The Original Moon                                                                                                         ...
Moon ABCs Fact Sheet   Property                  Earth                     Moon                        Brain Busters Equat...
Moon ABCs Fact Sheet  Property           Earth                     Moon                          Brain BustersCore        ...
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  1. 1. Education ProductNational Aeronautics and Teachers Grades 4–12Space Administration a Teacher’s Guide with activities for Earth and Space Sciences
  2. 2. a Teacher’s Guide with activities for Earth and Space Sciences National Aeronautics and Space Administration Office of Human Resources and Education Education Division Office of Space Science Solar System Exploration DivisionThis Publication is in the Public Domain and is not copyrighted.Permission is not required for duplication.November 1997EG-1997-10-116-HQ
  3. 3. my notes The following people contributedG. Jeffrey Taylor the activities in this book.Project CoordinatorProfessor Kathy ChockHawaii Institute of Geophysics and Planetology Hawaii Department of EducationSchool of Ocean and Earth Science and TechnologyUniversity of Hawaii at Manoa Pauline Higa Mililani High SchoolLinda M.V. MartelManaging Editor Art KimuraHawaii Institute of Geophysics and Planetology Future Flight HawaiiSchool of Ocean and Earth Science and TechnologyUniversity of Hawaii at Manoa Forrest Luke Leilehua High SchoolBrooks G. Bays, Jr.Designer Linda MartelPublication Services University of HawaiiSchool of Ocean and Earth Science and TechnologyUniversity of Hawaii at Manoa Dale Olive Waiakea High SchoolACKNOWLEDGMENTSThe activities were tested by teachers in classrooms Kevin Polkthroughout the state of Hawaii. We thank many University of Hawaiiindividuals in the Oklahoma State University Aero-space Education Services Program and at NASA Randolph ScovilleHeadquarters for their useful reviews of the materi- Highlands Intermediate Schoolals. We especially thank Pam Bacon and Greg Vogtfor all their help and encouragement. We also thank Liza Shigeta Kobayashithe Challenger Center for allowing a modification of Waiakea High Schoolthe Marsville activity on life support systems foruse in this book. Second edition revisions were Cheryl Shintanisupported by the Hawaii Space Grant Consortium. Koloa Elementary School Nancy TashimaAbout the cover Astronaut Ellison S. Onizuka Space CenterOur knowledge and concepts of the Moon changeover time as depicted by the three images. Jeff TaylorA map of the Moon (circa 1700s) is overlaid by University of Hawaiian Apollo 11 astronaut footprint (NASA photoAS11-40-5878) and a NASA painting of a future Arlene Yoshimuralunar habitation module by Pat Rawlings of Mililani Mauka Elementary SchoolScience Applications International Corporation.Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ i
  4. 4. Table of ContentsAbout This Book iiiAbout the Lunar Sample Disk ivAbout the Slide Set vActivity Matrices viTeachers Guide -- The Moon: Gateway to the Solar System 1Moon ABCs Fact Sheet 17Rock ABCs Fact Sheet 19Progress in Lunar Science Chart 20Nearside of the Moon--Apollo Landing Sites 21Unit 1 Pre-Apollo 23Resource Section for Unit 1 24Distance to the Moon 25Diameter of the Moon 29Reaping Rocks 33Unit 2 Learning From Apollo 37Resource Section for Unit 2 38The Lunar Disk 39Apollo Landing Sites 43Regolith Formation 47Lunar Surface 53Differentiation 57Impact Craters 61Clay Lava Flows 71Lava Layering 77Lunar Landing Sites 83Lunar Roving Vehicle 87Moon Anomalies 91Unit 3 The Future 99Resource Section for Unit 3 100Lunar Land Use 101Life Support Systems 109Lunar Biospheres 129Glossary 141Resources for Educators 145ii Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  5. 5. About this BookThese materials have been designed for use The length of time needed to complete anin upper elementary through high schools activity will vary according to the degree ofespecially, but not exclusively, with the difficulty and the development level of theLunar Sample Disk. See Page iv. students. Thus activities may take one to eight or more class periods.This book contains:• information on the Lunar Sample Disk, “Activity Matrices” are provided to assist• Activity Matrices -- Skills & Standards, in identifying the science process skills and• a Teacher’s Guide, science and mathematics educational stan-• Moon ABCs Fact Sheet, dards associated with each activity.• Rock ABCs Fact Sheet,• Progress in Lunar Science Chart, Classroom activities promote problem-• 17 activities, solving, communication skills, and team-• Resource Section for each unit, work. Each activity consists of teacher• Glossary, pages and reproducible student sheets.• NASA Educational Resources. Teacher pages begin with a statement of The “Teacher’s Guide” titled “The Moon: purpose and background information withGateway to the Solar System,” pages 1-16, answers specific to the activity. Relevantprovides background information about the pages in the “Teachers Guide” also areMoon. It tells the story of the Moon’s geo- listed. These are followed by sections onlogical history and how scientists try to deci- preparation, in-class suggestions, wrap-uppher the story. This background information ideas, and extensions. Words that are boldedmay be useful reading for students as well. appear in the Glossary.Key facts about the Moon appear on the“Moon ABCs” and “Rock ABCs” pages. Student sheets include a purpose state-These pages were named to emphasize ment, key words, list of materials, procedure,the basic nature of the information. The questions with space provided for answers,“Progress in Lunar Science Chart” summa- and charts. Key words are included in therizes our knowledge about the Moon from Glossary. Materials for each activity are1959 to 1997. listed in order of use. They are bolded in the text of the procedure section as a memory The activities are divided into three units: aid for students.Pre-Apollo, Learning from Apollo, and theFuture. These correspond, at least roughly, A note on measurements: These activitiesto exercises that can be done before the use metric units of measure with the fewLunar Sample Disk arrives at your school exceptions when English units are used to(Pre-Apollo), while it is there (Learning describe items from the material lists suchfrom Apollo), and after it has been returned as pans or measuring cups.to NASA (The Future).Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ iii
  6. 6. About the Lunar Sample DiskLegacy of Apollo How to Schedule a DiskThe collection of rocks and regolith from Educators must first be certified to bor-the Moon is a tangible legacy of the U.S. row lunar material by attending a trainingApollo Space Program. NASA makes a seminar on security requirements andsmall portion of this “extraterrestrial” proper handling procedures. This is thematerial available for classroom use same certification as for borrowing thethrough the Lunar Sample Loan Program. Meteorite Sample Disk. Then a written re- quest must be sent to a NASA EducatorLunar Sample Loan Resource Center at least one month prior toProgram the requested loan date. Contact the NASA Educator Resource Center that serves yourSix samples of rocks and regolith are geographic area for more information onembedded in a 15-cm diameter plastic disk. certification seminars and request pro-Disks are sent via registered mail to educators cedures (refer to Page 146 of this book forfor one- to two-week loan periods. The addresses and phone numbers.)package also includes this book Exploringthe Moon, an annotated slide set of lunarimages (described more fully on Page v), anda collection of color photographs and de-scriptions of the six samples. Ninth grade science students from Waipahu High School, Hawaii view the Lunar Sample Disk as part of an activity from Exploring the Moon . iv Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  7. 7. About the Slide SetThe Collection How to Obtain a CopyA set of thirty-six 35-mm slides has been It is easy to obtain a copy of the slides. Theyassembled to complement the activities in are available from the Central Operation ofthis book Exploring the Moon. Each slide Resources for Educators (CORE) in Ohio oris accompanied by detailed captions. Topics from NASA Educator Resource Centers.include what we knew about the Moon from Phone calls are welcome if you are unabletelescopic and other astronomic observa- to visit the Educator Resource Center thattions before Apollo, Apollo missions, astro- serves your geographic area. Please refer tonaut activities on the lunar surface, the High- Page 146 in this book for addresses andlands, the Maria, how the Moon formed, and phone numbers for CORE and Educatorexciting ideas for future explorations. Resource Centers. mple lt sa sa ba rake samples Apollo 15 siteExploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ v
  8. 8. Activity MatrixScience Process Skills Unit 1 Distance to the Moon Diameter of the Moon Pre- Apollo Reaping Rocks The Lunar Disk Unit 2 Apollo Landing Sites Learning From Regolith Formation Apollo Lunar Surface Differentiation Impact Craters Clay Lava Flows Lava Layering Lunar Landing Sites Lunar Roving Vehicle Moon Anomalies Lunar Land Use Unit 3 Life Support Systems Future Lunar Biospherevi Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  9. 9. Activity MatrixScience Standards Unit 1 Distance to the Moon Diameter of the Moon Pre- Apollo Reaping Rocks The Lunar Disk Unit 2 Apollo Landing Sites Learning From Regolith Formation Apollo Lunar Surface Differentiation Impact Craters Clay Lava Flows Lava Layering Lunar Landing Sites Lunar Roving Vehicle Moon Anomalies Lunar Land Use Unit 3 Life Support Systems Future Lunar BiosphereExploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ vii
  10. 10. Activity MatrixMathematics Standards Unit 1 Distance to the Moon Diameter of the Moon Pre- Apollo Reaping Rocks The Lunar Disk Unit 2 Apollo Landing Sites Learning From Regolith Formation Apollo Lunar Surface Differentiation Impact Craters Clay Lava Flows Lava Layering Lunar Landing Sites Lunar Roving Vehicle Moon Anomalies Lunar Land Use Unit 3 Life Support Systems Future Lunar Biosphereviii Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  11. 11. Teacher’s Guide THE MOON GATEWAY TO THE SOLAR SYSTEM G. Jeffrey Taylor, PhD WHEN ASTRONAUTS dug into theMoon’s surface during the Apollo program,they were doing more than digging up dry, darksediment. They were time travelers. The rocksand sediment returned by Apollo contain vitalclues to how Earth and the Moon formed, thenature and timing of early melting, the intensityof impact bombardment and its variation withtime, and even the history of the Sun. Most ofthis information, crucial parts of the story ofplanet Earth, cannot be learned by studyingrocks on Earth because our planet is so geologi-cally active that it has erased much of therecord. The clues have been lost in billions ofyears of mountain building, volcanism, weath-ering, and erosion. Colliding tectonic platesThe Moon, front and backThe top right photograph is a telescopic image of the Earth-facing halfof the Moon obtained at Lick Observatory in California. The one belowright was taken during the Apollo 16 mission and shows mostly the farside,except for the dark areas on the left, which can be seen, though barely,from Earth. The two major types of terrain are clearly visible. Thehighlands,which are especially well displayed in the photograph of the farside, arelight-colored and heavily cratered. The maria are darker and smoother;they formed when lava flows filled depressions. One of the mysteries aboutthe Moon is why fewer maria occur on the farside than nearside. Notehow many craters stand shoulder to shoulder on the farside. Theseimmense holes chronicle the Moon’s early bombardment, an intensebarrage that probably affected the early Earth as well.Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 1
  12. 12. and falling rain have erased much of Earth history, scopes were invented. Although we now know theyespecially the early years before four billion years ago. are not seas (the Moon never had any water), we still The Moon was geologically active in its heyday, use the term maria, and its singular form, mare.producing a fascinating array of products, but itsgeologic engine was not vigorous and all records of The highlands and cratersearly events were not lost. Its secrets are recorded inits craters, plains, and rocks. This guide reveals the Closer inspection shows that the highlands com-secrets that lunar scientists have uncovered since the prise countless overlapping craters, ranging in sizeApollo missions returned 382 kilograms (843 pounds) from the smallest visible in photographs (1 meter onof rock and sediment from the lovely body that the best Apollo photographs) to more than 1000 km.graces the night sky. Essentially all of these craters formed when meteor- The emphasis here is on geology. The samples ites crashed into the Moon. Before either robotic orreturned by Apollo are the stars of the show. [See the piloted spacecraft went to the Moon, many scientists“Lunar Disk” activity on Pages 39–42 and the thought that most lunar craters were volcanic in“Apollo Landing Sites” activity on Pages 43–46.] origin. But as we found out more about the nature ofUnderstanding the Moon, however, requires other lunar craters and studied impact craters on Earth, itgeological approaches, such as geological mapping became clear that the Moon has been bombarded byfrom high-quality photographs, the study of analo- cosmic projectiles. The samples returned by thegous features on Earth (for instance, impact craters), Apollo missions confirmed the pervasive role impactand experiments in laboratories. processes play in shaping the lunar landscape. The term “meteorite impact” is used to describeTHE LUNAR LANDSCAPE the process of surface bombardment by cosmic ob- ject. The objects themselves are variously referred to The Moon is not like Earth. It does not have oceans, as “impactors” or “projectiles.”lakes, rivers, or streams. It does not have wind-blown The impact process is explosive. A large impac-ice fields at its poles. Roses and morning glories do not tor does not simply bore its way into a planet’ssprout from its charcoal gray, dusty surface. Red- surface. When it hits, it is moving extremely fast,woods do not tower above its cratered ground. Dino- more than 20 km/sec (70,000 km/hour). This meet-saur foot prints cannot be found. Paramecium never ing is not tender. High-pressure waves are sent backconjugated, amoeba never split, and dogs never into the impactor and into the target planet. Thebarked. The wind never blew. People never lived impactor is so overwhelmed by the passage of thethere—but they have wondered about it for centu- shock wave that almost all of it vaporizes, never to beries, and a few lucky ones have even visited it. seen again. The target material is compressed strongly, then decompressed. A little is vaporized, some melted, Highlands and lowlands but most (a mass of about 10,000 times the mass of the impactor) is tossed out of the target area, piling up The major features of the Moon’s surface can be around the hole so produced. The bottom of the craterseen by just looking up at it. It has lighter and darker is lower than the original ground surface, the piled upareas. These distinctive terrains are the bright lunar material on the rim is higher. This is the characteristichighlands (also known as the lunar terrae, which is shape of an impact crater and is different fromLatin for “land”) and the darker plains called the volcanic calderas (no piled up materials) or cinderlunar maria, Latin for “seas,” which they resembled cones (the central pit is above the original groundto Thomas Hariot and Galileo Galilei, the first scien- surface). A small amount of the target is also tossedtists to examine the Moon with telescopes. The great distances along arcuate paths called rays.names terrae and maria were given to lunar terrains Real impacts cannot be readily simulated in aby Hariot and Galileo’s contemporary, Johannes classroom. In fact, there are very few facilities whereKepler. In fact, the idea that the highlands and maria we can simulate high-velocity impacts. Nevertheless,correspond to lands and seas appears to have been classroom experiments using marbles, ball bearings,popular among ancient Greeks long before tele- or other objects can still illustrate many important 2 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  13. 13. points about the impact process. For ex-ample, objects impacting at a variety ofvelocities (hence kinetic energies) producecraters with a variety of sizes; the moreenergy, the larger the crater. [See the “Im-pact Craters” activity on Pages 61–70.] The maria The maria cover 16% of the lunar sur-face and are composed of lava flows thatfilled relatively low places, mostly insideimmense impact basins. So, although theMoon does not have many volcanic cra-ters, it did experience volcanic activity.Close examination of the relationships be-tween the highlands and the maria showsthat this activity took place after the high-lands formed and after most of the crateringtook place. Thus, the maria are younger thanthe highlands. [See the “Clay Lava Flows”activity on Pages 71–76 and the “Lava Lay-ering” activity on Pages 77–82.] How do we know that the dark plainsare covered with lava flows? Why not someother kind of rock? Even before the Apollomissions brought back samples from themaria, there were strong suspicions that theplains were volcanic. They contain somefeatures that look very much like lava flows.Other features resemble lava channels, Rivers or lava channels?which form in some types of lava flows on The origin of river-like valleys, called rilles, was debated before the Apollo 15 mission visited one ofEarth. Still other features resemble col- them, Hadley Rille, shown here from orbit (white arrow shows the landing site) and from the lunarlapses along underground volcanic fea- surface. Some scientists argued that rilles were river valleys, implying that the Moon had flowingtures called lava tubes. These and other water at one time. Others thought that rilles resembled the channels that form in lava flows.features convinced most lunar scientists Observations by the Apollo 15 crew and samples returned settled the argument: rilles are volcanicbefore the Apollo missions that the maria features.were lava plains. This insight was con-firmed by samples collected from the maria: they logic mapping using high-quality telescopic images,are a type of volcanic rock called basalt. showed that the mare must be considerably younger The maria fill many of the gigantic impact basins than the basins in which they reside. For example, thethat decorate the Moon’s nearside. (The Moon keeps impact that formed the large Imbrium basin (thethe same hemisphere towards Earth because Earth’s Man-in-the-Moon’s right eye) hurled material out-gravity has locked in the Moon’s rotation.) Some wards and sculpted the mountains surrounding thescientists contended during the 1960s that this dem- Serenitatis basin (the left eye); thus, Serenitatis mustonstrated a cause and effect: impact caused not only be older. The Serenitatis basin is also home to Marethe formation of a large crater but led to melting of the Serenitatis. If the lavas in Mare Serentatis formedlunar interior as well. Thus, it was argued, the im- when the basin did, they ought to show the effects ofpacts triggered the volcanism. However, careful geo- the giant impact that formed Imbrium. They show noExploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 3
  14. 14. Maria mysteries Some mysteries persist about the maria. For one, why are volcanoes missing except for the cinder cones associated with dark mantle deposits? Sec- ond, if no obvious volcanoes exist, where did the lavas erupt from? In some cases, we can see that lava emerged from the margins of enormous impact ba- sins, perhaps along cracks concentric to the basin. But in most cases, we cannot see the places where the lava erupted. Another curious feature is that almost all the maria occur on the Earth-facing side of the Moon. Most scientists guess that this asymmetry is caused by the highlands crust being thicker on the lunar farside, making it difficult for basalts to make it all the way through to the surface. [See the “MoonLava flows dribbling across Mare Imbrium Anomalies” activity on Pages 91–98.]Long lava flows (lower left to upper right through center of photo) in Mare Imbrium.The flows are up to 400 kilometers long (the entire extent is not shown in this Apollo THE DUSTY LUNAR SURFACEphotograph) and have 30-meter high cliffs at their margins. The ridges running roughlyperpendicular to the flows are called wrinkle ridges. The ridges formed after the Some visitors to Kilauea Volcano, Hawai‘i, haveflows because they did not impede the advance of the lava flow. The smooth plains been overheard to say, upon seeing a vast landscapesurrounding the prominent lava flows are also lava, but older, so the margins are covered with fresh lava, “It looks just like the Moon.”harder to see. The craters on the right along the ridge are about 5 kilometers in Well, it doesn’t. The fresh lava flows of Kilauea anddiameter. other active volcanoes are usually dark grayish and barren like the Moon, but the resemblance endssigns of it. Furthermore, the maria contain far fewer there. The lunar surface is charcoal gray and sandy,craters than do basin deposits, hence have been with a sizable supply of fine sediment. Meteoritearound a shorter time (the older the surface, the impacts over billions of years have ground up thegreater the number of craters). The Apollo samples, formerly fresh surfaces into powder. Because theof course, confirmed these astute geological observa- Moon has virtually no atmosphere, even the tiniesttions and showed that the maria filling some basins meteorite strikes a defenseless surface at its fullformed a billion years after the basin formed. cosmic velocity, at least 20 km/sec. Some rocks lie One other type of deposit associated with the strewn about the surface, resembling boulders stick-maria, though it blankets highlands areas as well, is ing up through fresh snow on the slopes of Aspen orknown as dark mantle deposits. They cannot be seen Vail. Even these boulders won’t last long, maybe aexcept with telescopes or from spacecraft near the few hundred million years, before they are ground upMoon, but are important nonetheless. Before Apollo, into powder by the relentless rain of high-speedmost scientists believed that the dark mantle deposits projectiles. Of course, an occasional larger impactorwere formed by explosive volcanic eruptions known arrives, say the size of a car, and excavates fresh rockas pyroclastic eruptions (literally, “pieces of fire”). from beneath the blanket of powdery sediment. TheSome deposits seemed to be associated with low, meteoritic rain then begins to grind the fresh bouldersbroad, dark cinder cones, consistent with the idea that down, slowly but inevitably.they were formed by pyroclastic eruptions—this is The powdery blanket that covers the Moon ishow cinder cones form on Earth. This bit of geologic called the lunar regolith, a term for mechanicallydeduction was proven by the Apollo 17 mission and produced debris layers on planetary surfaces. Manyits sampling of the “orange soil,” a collection of tiny scientists also call it the “lunar soil,” but it containsglass droplets like those found in terrestrial pyro- none of the organic matter that occurs in soils onclastic eruptions. Earth. Some people use the term “sediment” for 4 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  15. 15. regolith. Be forewarned that the regolithsamples in the Lunar Sample Disk arelabeled “soil.” Although it is everywhere,the regolith is thin, ranging from abouttwo meters on the youngest maria toperhaps 20 meters in the oldest surfacesin the highlands. [See the “Regolith For-mation” activity on Pages 47–52.] Lunar regolith is a mixed blessing.On the one hand, it has mixed localmaterial so that a shovelful contains mostof the rock types that occur in an area. Iteven contains some rock fragments tossedin by impacts in remote regions. Thus,the regolith is a great rock collection. Italso contains the record of impacts dur-ing the past several hundred million toa billion years, crucial information forunderstanding the rate of impact onEarth during that time. On the otherhand, this impact record is not written Raking moon dirtvery clearly and we have not come close One of the most useful ways of obtaining samples of Moon rocks was to drag a rake through theto figuring it out as yet. The blanket of regolith. This allowed rock fragments larger than about one centimeter to remain on tines of the rake,regolith also greatly obscures the details while smaller fragments fell through. Note the large range in the sizes of rock fragments. One largeof the bedrock geology. This made field boulder lies near the rake, a medium-sized one is visible between the astronaut’s feet, along withwork during Apollo difficult and hinders countless other pebbles. Most of the regolith is smaller than fine sand. The astronaut’s footprints areour understanding of lunar history. distinct because the regolith is composed of a large percentage of tiny particles (about 20% is smaller The regolith consists of what you’d than 0.02 millimeters).expect from an impact-generated pileof debris. It contains rock and mineralfragments derived from the original bed-rock. It also contains glassy particlesformed by the impacts. In many lunarregoliths, half of the particles are com-posed of mineral fragments that are boundtogether by impact glass; scientists callthese objects agglutinates. The chemi-cal composition of the regolith reflectsthe composition of the bedrock under-neath. Regolith in the highlands is richin aluminum, as are highland rocks.Regolith in the maria is rich in iron andmagnesium, major constituents of ba-salt. A little bit of mixing from beneathbasalt layers or from distant highland A geologist-astronaut does field work on the Moonlocales occurs, but not enough to ob- Geologist Harrison H. Schmitt examines a large rock at the Apollo 17 landing site. This large boulderscure the basic difference between the contains numerous rock fragments that were smashed together by the huge impact event that madehighlands and the maria. the 750-kilometer Serentatis basin on the Moon.Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 5
  16. 16. One of the great potential bits of information MOON ROCKSstored in the complex pile atop the lunar surface is thehistory of the Sun. The nearest star puts out pro- Geologists learn an amazing amount about adigious amounts of particles called the solar wind. planet by examining photographs and using otherComposed mostly of hydrogen, helium, neon, car- types of remotely sensed data, but eventually theybon, and nitrogen, the solar wind particles strike the need to collect some samples. For example, althoughlunar surface and are implanted into mineral grains. geologists determined unambigously from photo-The amounts build up with time. In principle, we can graphs that the maria are younger than the highlands,determine if conditions inside the Sun have changed they did not know their absolute age, the age in years.over time by analyzing these solar wind products, Rocks also provide key tests to hypotheses. Forespecially the isotopic composition of them. instance, the maria were thought to be covered with The same solar wind gases may prove useful lava flows, but we did not know for sure until wewhen people establish permanent settlements on the collected samples from them. Also, no method canMoon. Life support systems require the life-giving accurately determine the chemical and mineralogi-elements: hydrogen and oxygen (for water), carbon, cal composition of a rock except laboratory analysis.and nitrogen. Plenty of oxygen is bound in the Most important, samples provide surprises, tellingsilicate, minerals of lunar rocks (about 50% by vol- us things we never expected. The highlands provideume) and the solar wind provided the rest. So, when the best example of a geological surprise, and onethe astronauts were digging up lunar regolith for with great consequences for our understanding ofreturn to Earth, they were not merely sampling— what Earth was like 4.5 billion years ago.they were prospecting!A fist-sized piece of the original lunar crustThis rock sample was collected during the Apollo 15 mission. It is an anorthosite, a Smash and mix, mix and meltrock composed of little else but the mineral feldspar. Anorthosites formed from the This rock returned by the Apollo 16 mission attests to the effects of impacts on aenormous magma system, the lunar magma ocean, that surrounded the newly planet’s crust. It is a hodgepodge of rock and mineral fragments, some of whichformed Moon. Because of its importance in understanding the origin of the Moon’s themselves are complicated mishmashes of rock debris. Geologists call thesecrust, the rock was nicknamed the “genesis rock.” complicated rocks breccias. 6 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  17. 17. Highland rocks, the lunar magma Hawaii developed a method to determine the iron ocean, and maybe a cataclysm content of the lunar surface from ratioes of the intensity of light reflected in different wavelengths. Strange as it may seem, the first highland rocks The magma ocean hypothesis predicts that the lunarwere collected during the first lunar landing, the highlands should have low iron contents, less thanApollo 11 mission, which landed on a mare, Mare about 5 wt. % (when recorded as iron oxide, FeO).Tranquillitatis. Although most of the rocks collected According to Clementine measurements, the high-were, indeed, basalts, some millimeter-sized rock lands average slightly under 5 wt. % FeO, consistentfragments were quite different. They were composed with the magma ocean idea. Further refinement ofchiefly of the mineral plagioclase feldspar; some this test is underway using data from Clementine andfragments were composed of nothing but plagio- the forthcoming U. S. Lunar Prospector Mission,clase. [See the “Rock ABCs Fact Sheet” on Page 19.] scheduled for launch in early 1998.Such rocks are called anorthosites. Some scientists The highlands also contain other types of igneoussuggested that these fragments were blasted to the rocks. The most abundant are called norites andApollo 11 landing site by distant impacts on highland troctolites, rocks composed of equal amounts ofterrain. Thus, they argued, the highlands are loaded plagioclase and either olivine or pyroxene (bothwith plagioclase. This was a bold extrapolation con- silicate minerals containing iron and magnesium).firmed by subsequent Apollo missions to highland Age dating suggests that these rocks are slightlysites. younger than the anorthosites and formed after the But this was not enough for some scientists. If magma ocean had crystallized.the highlands are enriched in plagioclase, how did Highland rocks are difficult to work with becausethey get that way? One way is to accumulate it by all that cratering, so evident in photographs of theflotation in a magma (molten rock). This happens highlands, has taken its toll on the rocks. Mostin thick subterranean magma bodies on Earth. highland rocks are complex mixtures of other rocks.So, plagioclase floated in a magma. But if ALL the The original igneous rocks have been melted, mixed,lunar highlands are enriched inplagioclase, then the magma musthave been all over the Moon. Theearly Moon must have been cov-ered by a global ocean of magma,now commonly referred to as thelunar magma ocean. Althoughsome scientists still remainunconvinced about the veracityof the magma ocean hypothesis,nothing we have learned since has contradicted the smashed, and generally abused by impacts during theidea that 4.5 billion years ago the Moon was covered Moon’s first half billion years. We call these compli-by a layer of magma hundreds of kilometers thick. cated rocks breccias. Some are so mixed up that theyThe idea has been extended to the young Earth as contain breccias within breccias within breccias.well, and even to Mars and some asteroids. And all Most of the anorthosites, norites, and troctolites arethis sprung forth because creative and bold scientists actually rock fragments inside breccias. Separatingsaw special importance in a few dozen white frag- them out is painstaking work.ments of anorthosite strewn about in a pile of char- An interesting thing about highland breccias,coal gray lunar regolith. especially those we call impact melt breccias (rocks The magma ocean concept was tested by the partly melted by an impact event), is that most of1994 U. S. Clementine Mission to the Moon. them fall into a relatively narrow span of ages, fromClementine was in a pole-to-pole orbit for two months, about 3.85 to 4.0 billion years. This has led someduring which it took thousands of photographs in scientists to propose (boldly again–lunar scientistsseveral wavelengths. Scientists at the University of don’t seem to be timid!) that the Moon wasExploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 7
  18. 18. bombarded with exceptional intensity during that potassium (chemical symbol K), rare-earth elementsnarrow time interval. If it happened, it probably (abbreviated REE), and phosphorus (P). Most Moonaffected Earth as well, perhaps leading to production specialists believe that KREEP represents the lastof the first sedimentary basins, and possibly inhibit- dregs from the crystallization of the magma ocean.ing the formation of the first life on this planet or Huge impacts dug down to the lower crust of theharming whatever life had developed by four billion Moon and excavated it, mixing it with other debrisyears ago. This idea of a cataclysmic bombardment to form KREEPy breccias.of the Moon is not yet proven. It could be that theapparent clustering in rock ages reflects poor sam- The maria:pling—we may only have obtained samples from lava flows and fountains of fireone or two large impact basins. The idea can be testedby obtaining samples from many more localities on The missions to mare areas brought back lots ofthe Moon. samples of basalt. Basalts differ from the highlands rocks in having more olivine and pyroxene, and less A piece of a lava flow This typical sample of a mare basalt is composed mostly of brown pyroxene (grayish in the photo) and white feldspar. The holes in the sample are frozen gas bubbles. Some basalt samples have many such bubbles (called vesicles by geologists), whereas others have none. plagioclase. Many of them also have surprisinglyMulti-ringed masterpieces large amounts of an iron-titanium oxide mineralThe Moon has about 35 multi-ringed, circular impact features larger than 300 km in called ilmenite. The first batch had so much ilmenitediameter. The one shown here, the Orientale basin, has three very prominent rings. (and some other related minerals) that they wereThe diameter of the outer one is 930 km. These immense craters might all have called “high-titanium” mare basalts, in honor of theformed in a narrow time interval between 3.85 and 4.0 billion years ago. Scientists exceptional titanium contents compared to terrestrialdo not know for sure how the rings form during the impact. basalts. The second mission, Apollo 12, returned basalts with lower titanium concentrations, so they Many highland breccias and a few igneous rocks were called “low-titanium” mare basalts. Subse-are enriched compared to other lunar samples in a quent missions, including an automated sample-set of elements not familiar to most of us. The return mission sent by the Soviet Union, returnedelements are those that tend not to enter the abundant some mare basalts with even lower titanium, sominerals in rocks. The result is that as a magma they were dubbed “very-low-titanium” basalts. Mostcrystallizes the part that is still liquid becomes scientists figure that mare basalts have a completeprogressively richer in these special elements. The range in titanium abundance. Data from the U. S.rocks that contain them are called KREEP, for Clementine Mission confirm this, and show that the 8 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  19. 19. Experiments conducted on mare basalts and pyroclastic glasses show that they formed when the interior of the Moon partially melted. (Rocks do not have a single melting tempera- ture like pure substances. Instead they melt over a range of tem- peratures: 1000–1200°C for some basalts, for example.) The experiments alsohigh-titanium basalts are not really very common on show that the melting took place at depths rangingthe Moon. from 100 to 500 km, and that the rocks that partially The shapes of the mineral grains and how they melted contained mostly olivine and pyroxene, withare intergrown in mare basalts indicate that these some ilmenite in the regions that formed the high-rocks formed in lava flows, some thin (perhaps a titanium basalts. An involved but sensible chain ofmeter thick), others thicker (up to perhaps 30 meters). reasoning indicates that these deep rocks rich inThis is not unusual for basalt flows on Earth. Many olivine and pyroxene formed from the lunar magmalunar mare basalts also contain holes, called vesicles, ocean: while plagioclase floated to form anorthositeswhich were formed by gas bubbles trapped when the in the highlands crust, the denser minerals olivinelava solidified. Earth basalts also have them. On and pyroxene sank. So, although the anorthosites andEarth, the abundant gases escaping from the lava are mare basalts differ drastically in age and composi-carbon dioxide and water vapor, accompanied by tion, the origins are intimately connected.some sulfur and chlorine gases. We are not as surewhat gases escaped from lunar lavas, although we What’s next?know that water vapor was not one of them becausethere are no hints for the presence of water or water- Scientists are still working on the bounty returnedbearing minerals in any Moon rock. The best bet is a by the Apollo missions. New analytical techniquesmixture of carbon dioxide and carbon monoxide, and improved understanding of how geological pro-with some sulfur gases added for good measure. cesses work keep the field exciting and vibrant. On Earth, when the amount of gas dissolved in Eventually we will need additional samples andmagma (the name for lava still underground) be- some extensive field work to fully understand thecomes large, it escapes violently and causes an Moon and how it came to be and continues to evolve.explosive eruption. In places such as Hawai‘i, for These sampling and field expeditions will probablyexample, the lava erupts in large fountains up to be done by a combination of robotic and pilotedseveral hundred meters high. The lava falls to the spacecraft.ground in small pieces, producing a pyroclastic de- In the meantime, Nature has provided a bonus:posit. This also happened on the Moon, producing samples from the Moon come to us free of charge inthe dark mantle deposits. One of these was sampled the form of lunar meteorites. (See companion vol-directly during the Apollo 17 mission. The sample, ume Exploring Meteorite Mysteries.) Thirteen sepa-called the “orange soil,” consists of numerous small rate meteorites have been identified so far, one foundorange glass beads. They are glass because they in Australia and the rest in Antarctica. We are surecooled rapidly, so there was not enough time to form that they come from the Moon on the basis ofand grow crystals in them. appearance and chemical and isotopic composition, Small samples of pyroclastic glasses were also but of course we do not know from where on thefound at other sites. Some are green, others yellow, Moon they come. These samples have helped sup-still others red. The differences in color reflect the port the magma ocean idea. Most important, know-amount of titanium they contain. The green have the ing that meteorites can be delivered to Earth byleast (about 1 weight percent) and the red contain the impacts on the Moon lends credence to the idea thatmost (14 weight percent), more than even the highest we have some meteorites from Mars. The Martiantitanium basalt.Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 9
  20. 20. meteorites are collectively called SNC meteorites. If mometers set up by the Apollo missions. Besideswe did not know so much about the Moon we would telling us how many and how strong moonquakesnever have been able to identify meteorites from the are, the data acquired by the Apollo seismic networkMoon, and, therefore, would not have been able to help us figure out something about the nature of theargue as convincingly that some meteorites come Moon’s interior. On Earth, seismology has allowedfrom Mars. us to know that the planet has a thin crust (20-60 km over continents, 8-10 km over ocean basins), a thick silicate mantle (down to 2900 km), and a large metallic iron core (2900 km to the center at 6370 km). The Moon is quite different. The crust is thicker than Earth’s continental crust, ranging from 70 km on the Earth-facing side to perhaps 150 km on the farside. The mare basalts represent a thin veneer on this mostly plagioclase-rich crust, averaging only about 1 km in thickness (inferred mostly from photogeological studies). Evidence from samples collected on the rims of the large basins Imbrium and Serentatis and from remote sensing instruments carried onboard two Apollo missions, the Clementine Mission, and the forthcoming Lunar Prospector Mission suggest that the lower crust may not contain as much plagio- clase as does the upper half of the crust. Beneath the crust is the lunar mantle, which is the largest part of the Moon. There might be a difference in rock typesFrom the Moon, free of charge above and below a depth of 500 km, perhaps repre-The first lunar meteorite discovered in Antarctica hails from the lunar highlands and, senting the depth of the lunar magma ocean. Beneathlike most highlands rocks, it is an impact breccia. The lunar meteorites prove that the mantle lies a small lunar core made of metallicobjects can be blasted off sizable objects without melting them, adding credence to iron. The size of the core is highly uncertain, withthe idea that a group of twelve meteorites comes from Mars. estimates ranging from about 100 km to 400 km. That little core is important, though. The MoonMOONQUAKES, THE MOON’S does not have much of a magnetic field, so the lunarINTERIOR, AND THE MYSTERIOUS core is not generating magnetism the way Earth’sMAGNETIC FIELD core is. Nevertheless, it did in the past. Lunar rocks are magnetized, and the strength of the magnetic field The Moon does not shake, rattle, and roll as Earth has been measured by special techniques. Also, olderdoes. Almost all moonquakes are smaller than Earth’s rocks have stronger magnetism, suggesting that theconstant grumblings. The largest quakes reach only Moon’s magnetic field was stronger in the distantabout magnitude 5 (strong enough to cause dishes to past, and then decreased to its weak present state.fall out of cabinets), and these occur about once a Why this happened is unknown. What is known isyear. This is clear evidence that the Moon is not at this: you cannot navigate around the Moon using apresent geologically active. No internal motions compass!drive crustal plates as on Earth, or initiate hot spots There are other mysteries about the Moon’sto give rise to volcanic provinces like Hawai‘i. This magnetism. Although the field was always weak andseismic inactivity is a wonderful virtue in the eyes is extremely weak now, there are small areas on theof astronomers. Combined with the lack of an Moon that have magnetic fields much stronger thanatmosphere to cause stars to twinkle, the low moon- the surrounding regions. These magnetic anomaliesquake activity makes the Moon an ideal place to have not been figured out. Some scientists haveinstall telescopes. associated them with the effects of large, basin- We know about moonquakes from four seis- forming impacts. Others have suggested that the 10 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  21. 21. Moon forming together, a two-body system from the start. This idea has trouble explaining Earth’s rotation rate and how the moon-forming material got into orbit around Earth and stayed there, rather than falling to Earth. (These problems with to- tal amount of spinning involve both Earth’s rotation and the Moon’s motion around Earth. The amount of rotation and revolving is quantified by a physical property called angular momentum.) The problem was so frustrating that some scientists suggested that maybe science had proved that the Moon does not exist! The annoying problems withInside the Moon and Earth the classical hypotheses of lunarScientists have learned what Earth and the Moon are like inside by several techniques, the most important origin led scientists to consider al-of which is seismology, the study of earthquake (and, of course) moonquake waves. Earth has a much ternatives. This search led to thelarger metallic core than does the Moon. seemingly outlandish idea that the Moon formed when a projectile theionized gases produced when comets impact the size of the planet Mars (half Earth’s radius and one-Moon might give rise to strong magnetic anomalies tenth its mass) smashed into Earth when it had grownin the crater ejecta. The jury is still out. The Lunar to about 90% of its present size. The resulting explo-Prospector Mission will thoroughly map the distri- sion sent vast quantities of heated material into orbitbution of magnetic anomalies, perhaps helping to around Earth, and the Moon formed from this debris.solve this mystery. This new hypothesis, which blossomed in 1984 from seeds planted in the mid-1970s, is called the giantTHE MOON’S ORIGIN: A BIG WHACK impact theory. It explains the way Earth spins andON THE GROWING EARTH why Earth has a larger metallic core than does the Moon. Furthermore, modern theories for how the For a long time, the most elusive mystery about planets are assembled from smaller bodies, whichthe Moon was how it formed. The problem baffled were assembled from still smaller ones, predict thatphilosophers and scientists for hundreds of years. All when Earth was almost done forming, there wouldof the hypotheses advanced for lunar origin had fatal have been a body nearby with a mass about one-tenthflaws, even though partisans tried tenaciously to that of Earth. Thus, the giant impact hypothesized toexplain away the defects. The capture hypothesis, have formed the Moon is not an implausible event.which depicts capture of a fully formed Moon by The chances are so high, in fact, that it might haveEarth, suffered from improbability. Close encounter been unavoidable.with Earth would either result in a collision or fling One would think that an impact between anthe Moon into a different orbit around the Sun, almost Earth-sized planet and a Mars-sized planetprobably never to meet up with Earth again. The would be catastrophic. The energy involved is in-fission hypothesis, in which the primitive Earth spins comprehensible. Much more than a trillion trillionso fast that a blob flies off, could not explain how tons of material vaporized and melted. In someEarth got to be spinning so fast (once every 2.5 hours) places in the cloud around the Earth, temperaturesand why Earth and the Moon no longer spin that fast. exceeded 10,000°C. A fledgling planet the size ofThe double-planet hypothesis pictures Earth and the Mars was incorporated into Earth, its metallic coreExploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 11
  22. 22. and all, never to be seen again. Yes, this sounds was at least 500 km deep. The first minerals to formcatastrophic. But out of it all, the Moon was created in this mind-boggling magmatic system were theand Earth grew to almost its final size. Without this iron and magnesium silicates olivine and pyroxene.violent event early in the Solar System’s history, They were denser than the magma, so they sank, likethere would be no Moon in Earth’s sky, and Earth rocks in a pond, though not as fast. Eventually,would not be rotating as fast as it is because the big plagioclase feldspar formed, and because it was lessimpact spun it up. Days might even last a year. But dense than the magma, began to float to the top, likethen, maybe we would not be here to notice. bubbles in cola. It accumulated and produced moun- tains of anorthosite, producing the first lunar crust. The magma ocean phase ended by about 4.4 billion years ago. [See the “Differentiation” activity on Pages 57–60.]WHACK!The Moon may have formed when an object the size of the planet Mars smashedinto Earth when our future home was about 90% constructed. This fierce eventmade Earth larger and blasted off vaporized and melted material into orbit. TheMoon formed from this debris. This painting was created by William K. Hartmann,one of the scientists who invented the giant impact hypothesis for lunar origin.A BRIEF HISTORY OF THE MOON Sinking and floating in an ocean of magma We know the general outlines of what happened Soon after it formed, the Moon was surrounded by a huge shell of molten rockto the Moon after it was formed by a giant impact. called the lunar magma ocean. As crystals formed in it, the denser ones such asThe first notable event, which may have been a olivine and pyroxene sank and the less dense ones, such as feldspar, floatedconsequence of the giant impact, was the formation upwards, forming the original anorthosite crust on the Moon. Dropping toothpicksand crystallization of the magma ocean. Nobody and pennies into a glass of water shows the process: the toothpicks (representingknows how deep it was, but the best guess is that it feldspar) float and the pennies (olivine and pyroxene) sink. 12 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  23. 23. Almost as soon as the crust had formed, perhaps 110 million years ago. This, therefore, is the age ofwhile it was still forming, other types of magmas that the crater Tycho. It is a triumph of geological savvywould form the norites and troctolites in the high- that we were able to date an impact crater that lieslands crust began to form deep in the Moon. A great over 2000 km from the place we landed!mystery is where inside the Moon and how deep. The impacts during the past billions of years alsoMany lunar specialists believe the magmas derived have mixed the upper several meters of crust to makefrom unmelted Moon stuff beneath the magma ocean. the powdery lunar regolith. The Sun has continued toIn any case, these magmas rose and infiltrated the implant a tiny amount of itself into the regolith,anorthosite crust, forming large and small rock bod- giving us its cryptic record and providing resourcesies, and perhaps even erupting onto the surface. for future explorers. And recently, only seconds agoSome of the magmas reacted chemically with the in geologic time, a few interplanetary travelers leftdregs of the magma ocean (KREEP) and others may their footprints here and there on the dusty ground.have dissolved some of the anorthosite. This periodof lunar history ended about 4.0 billion years ago. All during these first epochs, left-over projectilescontinued to bombard the Moon, modifying therocks soon after they formed. The crust was mixed toa depth of at least a few kilometers, perhaps as muchas 20 km, as if a gigantic tractor had plowed the lunarcrust. Though not yet proven, the rate of impact mayhave declined between 4.5 and 4.0 billion years ago,but then grew dramatically, producing most of the largebasins visible on the Moon. This cataclysmic bom-bardment is postulated to have lasted from 4.0 to 3.85billion years ago. [See the “Impact Craters” activityon Pages 61–70, and the “Regolith Formation”activity on Pages 47–52.] Once the bombardment rate had settled down,the maria could form. Basalts like those making upthe dark mare surfaces formed before 3.85 billion Anatomy of an impact crateryears ago, but not as voluminously as later, and the The crater Tycho in the southern highlands on the lunar nearside is 85 kilometersenormous bombardment rate demolished whatever across. Its terraced walls rise 3 to 4 kilometers above its floor. Its rim rises above thelava plains formed. However, between 3.7 and about surrounding terrain, and its floor sits below it. Smooth material on the floor of the2.5 billion years ago (the lower limit is highly uncer- crater consists of impact-melted rock that flowed like lava across the growing floortain), lavas flowed across the lunar surface, forming in the later stages of excavation. In response to the huge increase then decrease inthe maria and decorating the Moon’s face. Along with pressure, mountains two kilometers high rose from its floor, bringing up materialthe basalts came pyroclastic eruptions, high foun- from as much as ten kilometers in the crust. The blanket of material surrounding thetains of fire that launched glowing droplets of molten crater is called the ejecta blanket; this pile of debris becomes progressively thinnerbasalt on flights up to a few hundred kilometers. away from the crater (especially evident on the left of the photo). Since mare volcanism ceased, impact has beenthe only geological force at work on the Moon. Some Although not visible on this photograph, large craters like Tycho also have raysimpressive craters have been made, such as emanating from them. Rays form when materials thrown out of the crater land andCopernicus (90 km across) and Tycho (85 km). excavate more of the lunar landscape along arcuate paths. The Tycho event causedThese flung bright rays of material across the dark a landslide and several secondary impacts at the Apollo 17 landing site, over 2000lunar landscape, adding more decoration. In fact, kilometers away. Analysis of samples collected during the Apollo 17 mission indicatessome of the material blasted from Tycho caused a that these events took place 110 million years ago. Thus, Tycho formed 110 milliondebris slide at what would become the Apollo 17 years ago.landing site. Samples from this site indicate that thelandslide and some associated craters formed aboutExploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 13
  24. 24. THE MOON AND EARTH: extinctions are not understood. One possibility is thatINEXORABLY INTERTWINED some mass-extinction events were caused by peri- odic increases in the rate of impact on Earth. For The Moon ought to be especially alluring to example, the mass extinctions, which included thepeople curious about Earth. The two bodies formed demise of the dinosaurs, at the end of the Cretaceousnear each other, formed mantles and crusts early, period (65 million years ago), may have been causedshared the same post-formational bombardment, and by a large impact event. Attempts to test the idea byhave been bathed in the same flux of sunlight and dating impact craters on Earth are doomed becausesolar particles for the past 4.5 billion years. Here are there are too few of them. But the Moon has plentya few examples of the surprising ways in which lunar of craters formed during the past 600 million yearsscience can contribute to understanding how Earth (the period for which we have a rich fossil record).works and to unraveling its geological history. These could be dated and the reality of spikes in the Origin of the Earth-Moon System. No matter how impact record could be tested.the Moon formed, its creation must have had dra- How geologic processes operate. The Moon is amatic effects on Earth. Although most scientists have natural laboratory for the study of some of the geo-concluded that the Moon formed as a result of an logic processes that have shaped Earth. It is a greatenormous impact onto the growing Earth, we do not place to study the details of how impact craters formknow much about the details of that stupendous because there are so many well-preserved craters inevent. We do not know if the Moon was made mostly an enormous range of sizes. It is also one of the placesfrom Earth materials or mostly projectile, the kinds where volcanism has operated, but at lower gravityof chemical reactions that would have taken place in than on either Earth or Mars.the melt-vapor cloud, and precisely how the Moonwas assembled from this cloud. LIFE AND WORK AT Magma oceans. The concept that the Moon had a A MOON BASEmagma ocean has been a central tenet of lunar sci-ence since it sprung from fertile minds after the People will someday return to the Moon. Whenreturn of the first lunar samples in 1969. It is now they do, it will be to stay. They will build a base onbeing applied to Earth, Mars, and asteroids. This the Moon, the first settlement in the beginning of anview of the early stages of planet development is interplanetary migration that will eventually takevastly different from the view in the 1950s and them throughout the Solar System.1960s. Back then, most (not all) scientists believed There will be lots to do at a lunar base. Geologiststhe planets assembled cold, and then heated up. The will study the Moon with the intensity and vigorrealization that the Moon had a magma ocean changed they do on Earth, with emphasis on field studies.all that and has led to a whole new way of looking at Astronomers will make magnificent observations ofEarth’s earliest history. the universe. Solar scientists will study the solar Early bombardment history of Earth and Moon. wind directly and investigate past activity trapped inThe thousands of craters on the Moon’s surface layers of regolith. Writers and artists will be inspiredchronicle the impact record of Earth. Most of the by a landscape so different from Earth’s. Life scien-craters formed before 3.9 billion years ago. Some tists will study how people adapt to a gravity fieldscientists argue that the Moon suffered a cataclysmic one-sixth as strong as Earth’s, and figure out how tobombardment (a drastic increase in the number of grow plants in lunar greenhouses. Engineers willimpacting projectiles) between 3.85 and 4.0 billion investigate how to keep a complex facility operatingyears ago. If this happened and Earth was subjected continuously in a hostile environment. Mining andto the blitzkrieg as well, then development of Earth’s chemical engineers will determine how to extractearliest crust would have been affected. The intense resources from Moon rocks and regolith. The seem-bombardment could also have influenced the devel- ingly dry lunar surface contains plenty of the ingre-opment of life, perhaps delaying its appearance. dients to support life at a Moon base (oxygen and Impacts, extinctions, and the evolution of life on hydrogen for water, nitrogen and carbon for theEarth. The mechanisms of evolution and mass growth of plants), including the construction 14 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  25. 25. The Curatorial Facil- ity is one of the cleanest places you’ll ever see. To go inside, you must wear white suits, boots, hats, and gloves, outfits affection- ately known as “bunny suits.” Wipe a gloved hand on a stainless steel cabinet and you will not find a trace of dust because the air is filtered to remove potential contaminating particles. The samples are stored in a large vault, and only one at a time is moved to a glove box. You can pick up the rocks by jammingGeology at a Moon Base your hands into a pair ofThe best geology is done in the field. To understand rocks we must examine them up close, map their distributions, see the the black rubber gloves,structures in them, and chip off samples when necessary. The field geology done during the Apollo missions was hampered allowing you to turn a rockby the lack of time the astronauts could devote to it. But that will change when people live permanently on the Moon. over, to sense its mass andGeologists will be able to spend as much time as they need to decipher the story recorded by lunar rock formations. This density, to connect with it.painting shows three astronauts (one in the distance) examining the outside of a lava tube, an underground conduit that A stereomicroscope al-carried red-hot lava to an eruption site perhaps hundreds of kilometers away. lows you to look at it closely. If you decide you need a sample, and of course you have been approvedmaterials to build and maintain the base (regolith to obtain one, then expert lunar sample processorscan be molded into bricks; iron, titanium, and alumi- take over. The sample is photographed before andnum can be smelted and forged into tools and build- after the new sample is chipped off. This is timeing materials). It will be an exciting, high-tech, consuming, but valuable to be sure we know thefaraway place inhabited by adventurous souls. [See relationships of all samples to each other. In manythe Unit 3 activities beginning on Page 99.] cases, we can determine the orientation a specific part of a rock was in on the surface of the MoonWHERE MOON ROCKS before collection.HANG OUT A select small number of pieces of the Moon are on display in public museums, and only three pieces Since arrival on Earth, lunar samples have been can actually be touched. These so-called lunartreated with the respect they deserve. Most of the "touchstones" were all cut from the same Apollo 17treasure of Apollo is stored at the Lunar Curatorial basaltic rock. One touchstone is housed at theFacility at the Johnson Space Center, Houston, Texas. Smithsonian Air and Space Museum in Washington,A small percentage is stored in an auxiliary facility at D.C. Another touchstone is at the Space CenterBrooks Air Force Base near San Antonio, Texas, Houston facility adjacent to the Johnson Space Cen-placed there in case a disaster, such as a hurricane, ter. A third touchstone is on long-term loan to thebefalls Houston and the samples are destroyed. Many Museo de Las Ciencias at the Universidad Nacionalsmall samples are also in the laboratories of investi- Autonoma de Mexico. Visitors to these exhibitsgators around the world, where enthusiastic scien- marvel at the unique experience of touching a piecetists keep trying to wring out the Moon’s secrets. of the Moon with their bare hands.Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 15
  26. 26. The Original Moon Four and a half æons ago a dark, dusty cloud deformed. Sun became star; Earth became large, and Moon, a new world, was born. This Earth/Moon pair, once linked so close, would later be forced apart. Images of young intimate ties we only perceive in part. Both Earth and Moon were strongly stripped of their mantle siderophiles. But Moon alone was doomed to thirst from depletion of volatiles.Safe haven for precious rocksNASA stores the lunar sample collection in a specially constructed facility called the Lunar Curatorial Moon holds secrets of ages pastFacility at the Johnson Space Center in Houston, Texas. The priceless materials remain in a nitrogen when planets dueled for space.atmosphere, which is far less reactive chemically than normal oxygen-rich air. Scientists working in the As primordial crust evolvedfacility wear lint-free outfits affectionately known as “bunny suits,” and handle the samples in glove raw violence reworked Moon’s face.boxes. In this photograph, Roberta Score is examining a piece of an Apollo 16 rock, while Andrea Mosie After the first half billion years(left) looks on. huge permanent scars appeared; ancient feldspathic crust survived with a mafic mantle mirror. But then there grew from half-lived depths a new warmth set free inside.SCIENTISTS AS POETS Rivers and floods of partial melt resurfaced the low ‘frontside’. Scientists do not view the world in purely objective ways. Thus evolved the Original MoonEach has biases and a unique way of looking at the world. Science in those turbulent times.is not done solely with piles of data, hundreds of graphs, or pages Now we paint from fragments of cluesof equations. It is done with the heart and soul, too. Sometimes the reasons and the rhymes:a scientist is moved to write about it in elegant prose like thatwritten by Loren Eisley or in poetry, like the poem written by Sister planet;Professor Carlé Pieters of Brown University. Dr. Pieters holds Modified clone; Captured migrant;her doctorate from MIT and is an expert in remote sensing of Big splash disowned?planetary surfaces. She is especially well known for her tele-scopic observations of the Moon. The poem first appeared in the The Truth in some or all of thesefrontispiece of Origin of the Moon, published by the Lunar and will tickle, delight,Planetary Institute. temper, and tease. — Carlé Pieters 16 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ
  27. 27. Moon ABCs Fact Sheet Property Earth Moon Brain Busters Equatorial 12,756 km 3,476 km How long would it take to drive diameter around the Moons equator at 80 km per hour? Surface area 510 million 37.8 million The Moons surface area is square km square km similar to that of one of Earths continents. Which one? Mass 5.98 x 1024 kg 7.35 x 1022 kg What percentage of Earths mass is the Moons mass? Volume --- --- Can you calculate the volumes of Earth and the Moon? Density 5.52 grams per 3.34 grams per Check this by calculating the cubic cm cubic cm density from the mass and volume. Surface 9.8 m/sec/sec 1.63 m/sec/sec What fraction of Earths gravity is gravity the Moons gravity? Crust Silicate rocks. Silicate rocks. What portion of each body is Continents Highlands crust? dominated by dominated by granites. Ocean feldspar-rich crust dominated rocks and maria by basalt. by basalt. Mantle Silicate rocks Similar to Earth. Collect some silicate rocks and dominated by determine the density. Is the minerals density greater or lesser than the containing iron Earth/Moons density? Why? and magnesium.Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ 17
  28. 28. Moon ABCs Fact Sheet Property Earth Moon Brain BustersCore Iron, nickel metal Same, but core is What portion of each body is much smaller core?Sediment or Silicon and Silicon and oxygen Do you think life ever existedRegolith oxygen bound in bound in minerals, on the Moon? minerals that glass produced by Why or why not? contain water, meteorite impacts, plus organic small amounts of materials. gases (e.g., hydrogen) implanted by the solar wind. No water or organic materials.Atmosphere 78 % nitrogen, Basically none. Some Could you breathe the lunar(main 21 % oxygen carbon gases (CO2 , atmosphere?constituents) CO, and methane), but very little of them. Pressure is about one- trillionth of Earths atmospheric pressure.Length of day 23.93 hours 27.3 Earth days How long does daylight last (sidereal on the Moon? rotation period)Surface Air temperature Surface temperature Why are the temperatures oftemperature ranges from ranges from -193oC Earth and the Moon so -88oC (winter in (night in polar different? polar regions) to regions) to 111 Co o 58 C (summer in (day in equatorial tropical regions). regions).Surface 25 % land 84 % heavily-cratered Compare maps of Earth andfeatures (seven continents) highlands. the Moon. Is there any with varied terrain 16 % basalt-covered evidence that plate tectonics of mountains, maria. operated on the Moon? plains, river val- Impact craters-- leys. Ocean floor some with bright rays, characterized by crater chains, and mountains, plains. rilles.18 Exploring the Moon -- A Teachers Guide with Activities, NASA EG-1997-10-116-HQ

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