Mather, Kirtley F.

English

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 26 Article 5 1972 Moon, Then and Now Kirtley F. Mather Harvard University Follow this and additional works at: https://scholarworks.uark.edu/jaas Recommended Citation Mather, Kirtley F. (1972) "Moon, Then and Now," Journal of the Arkansas Academy of Science: Vol. 26 , Article 5. Available at: https://scholarworks.uark.edu/jaas/vol26/iss1/5 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. Arkansas Academy of Science Proceedings, Vol. XXVI,1972 11The Moon, Then and NowKIRTLEYF.MATHERProfessor of Geology, Emeritus, Harvard University, Cambridge, Massachusetts*FOREWORDDr. Mather wrote this article on the state ofmoon research in honor of the University ofArkansas Centennial Celebration and the specialexhibition of lunar material at the UniversityMuseum in connection with the 1972 meeting ofthe Arkansas Academy of Science at Fayetteville.The paper was written at the express request of Dr.Samuel C. Dellinger, Emeritus Professor ofZoology and former curator of the Museum at theUniversity of Arkansas. Dr. Mather taught geologyat the University of Arkansas from 1911 to 1914,and later was professor of geology at HarvardUniversity for nearly 30 years. He was awarded hisPh.D from the University of Chicago, wasassociated with the U.S. Geological Survey fornearly 35 years, and has received a number ofhonorary degrees. He has been a member andofficer of numerous professional organizations,and is a past president of the AmericanAssociation for the Advancement of Science. Dr.Mather is a prolificauthor, having produced manytechnical and popular works in the fields ofgeology, physiography, and education over thepast half century.The moon has changed scarcely at all since the University ofArkansas was founded in 1871 ,but our knowledge about it hasncreased by several orders ofmagnitude, most spectacularly asresult of the "moon walks" performed by Apollo astronautsince 20 July 1969. Anyone interested in selenology-the>eology ofthe moon--cannot but be thrilled by even the mostasual inspection of the samples of the moon's surfacematerials that they brought back to earth.IThis is not to say, however, that not much was known aboute moon ahundred years ago. Using his home-made telescope,Galileo (1564-1642) had published sketches of the moon'ssurface in 1609 showing several ofits largest craters, mountainranges, and irregularly circular plains. Those plains weredesignated as "maria" by Riccioli (1598-1671) in his notable"book about the moon," published in 1651. Init he named aarge number of the craters for famous scientists and)hilosophers, and gave highly imaginative names to many oflemaria. The majority ofRiccioli's names are still used todaynd some of them are now familiar to millions of people as aesult of coverage of the exploits of the Apollo crews by theews media; for example, Mare Tranquillitatis (the Sea ofranquillity), Mare Imbrium (the Imbrium Basin), and theraters named Copernicus and Archimedes.tLikewise, the 16th to 18th century astronomers hadmputed with increasing accuracy the size, mass, and averageecific gravity ofthe moon and its tidal effects on the earth asrevolved around our planet. The years since 1871 havetnessed only somewhat greater precision of measurementsncerning those bits of information. On the other hand,completely new instruments and techniques for observation ofPresent address: 1044 Stanford Drive. NEAlbuquerque, NM 87106such a remote object have been invented during those years andespecially during the last 10 or 15 of them. Combining theseinventions with the new physics and chemistry of "the atomicage" and the techniques of space transportation developed inthe even newer "space age," modern science and technologyhave given us an amazing amount of information about themoon.The colossal task of analyzing, correlating, and interpretingthe vast store of factual data now available is proceeding inhundreds of scientific laboratories around the world, but it hasbyno means been completed. Some important questions aboutthe moon and its history still remain unanswered. Even so, thewild, free-wheeling speculations, rampant a century or moreago, are now replaced by a few carefully restricted workinghypotheses, and a number ofsignificant generalizations may bestated with great confidence.The moon is composed ofrocks and minerals nearly the sameas rocks and minerals found here on earth. It came intoexistence approximately 4.6 billion years ago, at the same timeas the earth. Most selenologists consider that itwas formed byaccretion of planetesimals orbiting the growing earth andothers orbiting the sun. During the first 1.5 billion years ofitshistory, its thermal processes and internal activity wereprobably quite similar to those of the juvenile earth. Since then,unlike the earth, itapparently has been a slowly cooling bodylacking any significant deep-seated internal activity.Furthermore, because ofits small size, the moon has never hadsufficient gravitational force to retain an atmosphere andhydrosphere that could engender processes of erosion andsedimentation like those that have played an important role inthe evolution of the earth.Evidence from three seismometers (instruments that measuremoonquakes in the same way as earthquakes) left on themoon's surface by Apollo astronauts indicates that the moonhas a layered crust approximately 65 km (about 40 mi) thick,and there is some suggestion from the remanentpaleomagnetism detected in "moon rocks" that the moon hasan iron core which was molten during its infancy. Ifso, thatcore cannot have a radius greater than 0.2 the radius of themoon and it is therefore relatively much smaller than theearth's core. However, there is nothing to indicate that theinternal structure ofthe moon comprises a convective mantleresembling dynamically that portion of the earth between itscore and crust.Samples of the moon's surface materials from five ratherwidely scattered sites now have been studied directly here onearth. The specimens from one of the five localities werescooped up and retrieved by the unmanned USSR Luna 16spacecraft; the others were collected by the crews of Apollo11,12, 14, and 15. The petrologists report that the specimens theyhave studied represent three major types ofrock and fragmentsderived from them. The oldest are rather coarsely crystallizedigneous rocks, such as anorthosite, composed largely ofplagioclase feldspar, that were formed by comparatively slowcrystallization from fairly large bodies ofmolten magma about4 billion years ago. They are characteristic of the moon'shighlands and include David Scott's "genesis rock" (identified11Journal of the Arkansas Academy of Science, Vol. 26 [1972], Art. 5Published by Arkansas Academy of Science, 1972Iii12 Arkansas Academy of Science Proceedings, Vol.XXVI,1972IKirtleyF.Matherby Scott as anorthosite while he was on the moon during theApollo 15 mission; the designation "genesis rock" waspromptly coined by a reporter in Houston and has since beenwidely used). They come as close to representing thecomponents ofthe original lunar surface as we are likely to get.Intermediate in age is a basaltic type of fine-grained igneousrock, notably rich inpotassium (symbol K),rare earth elements(symbol REE), and phosphorus (symbol P), and hence called"KREEP basalt." Many fragments of this kind of basalt werescattered around by the impact ofincoming meteorites, most ofwhich were much smaller than the huge projectile responsiblefor forming the Imbrium Basin, just beyond the rim of whichApollo 15 landed. The third major type of rock consists of>asalts much more similar to those at many places on theearth's surface; they are sometimes referred to as "normal>asalts" in contrast to the older "KREEP basalts." Allof theocks thus far dated by radioactive methods are between 3.1and 3.7 billion years old. They occur characteristically as lavalows that flooded pre-existing basins-most, ifnot all of whichwere formed by impacting meteorites-to produce the existingmaria.Fragments of these ancient rocks were scattered by theexplosive impact of meteorites bombarding the face of themoon during the last 3 billion years, in general in decreasingnumbers as the millenia went by. In some places theirdistribution is in a pattern of rays, radiating from craters likeCopernicus. In many places where they accumulated to aconsiderable thickness, the fragments form breccias, solidifieday compaction under the weight of the overburden or bycementation by shock-melted glass. Some of the loosefragments in the rock collections are glazed on one or moresides by such glass. This material is particularly abundant inthe "fines" of the lunar samples.Ingeneral the relative age of the craters that pockmark themoon's surface can be inferred from the extent of rounding orsoftening of their originally sharp peripheral rims. Rocks areFractured and shattered by expansion and contraction due tohe great changes in surface temperature between the excessiveleat of the long days and the deep freeze of the long nightseach equal in length to 14 earth days). Gravity pulls theloosened particles down slope, even though its force on themoon is about one-fifth of its force at the surface of the earth.Lunar talus slopes and cones are similar to analogousandforms on earth. The impact of micrometeorites may movedust particles fromplace to place inmuch the same way as theyare moved about by terrestrial breezes. Almost everywhere thesolid rock of the lunar crust is veneered with lunar "soil"--jetter designated as regolith--from a few centimeters to manymeters thick. Fortunately the loose particles of the lunarregolith are compacted rapidly under their own weight so that'moon walkers" and their vehicles leave footprints and tracksbut do not sink far into the regolith.The overwhelming majority ofthe lunar craters were formedby impact ofmeteorites or planetesimals; they are definitely notofvolcanic origin. Infact, outpouring oflava and other kinds ofvolcanic activity seem to have ceased, for all practical purposes,some 3 billion years ago. Even so, there is still a slightpossibility that some volcanic cones and /or craters may yet beidentified as exploration ofthe moon continues, and that recentor even currently active volcanism may be detected somewhereon its surface. The report from the Soviet Union that anemission ofgas from the crater Alphonsus was observed in1958should not be totally discarded as an aberration of instrumentsor men, even though that observation has never been confirmedor repeated elsewhere.The age-old question as to whether there is life on the moon,even though itmight be some kind of livingcreature whollydifferent from any known on earth, has now been answeredquite definitely in the negative. According to N.W. Hinners(1971, p. 448): "...no life forms have been found, nor haveorganic molecules been unambiguously identified as beingindigenous to the moon. The virtually complete lack of waterand the four-plus billion years of exposure to a harsh spaceenvironment make eventual detection of lunar life unlikely."ACKNOWLEDGMENTSThe writer thanks Dr. Klaus Keil, Director ofthe Institute of Meteoritics, University of NewMexico, for supplying helpful documents andreading critically the first draft of this article. Thewriter, however, is solely responsible for itscontents, including any inadvertent errors it maycontain.REFERENCESAPOLLO 15PRELIMINARYEXAMINATIONTEAM. 1972.The Apollo 15 lunar samples: a preliminary description.Science 175:363-375.BAUMGARTEN, PETER (Editor and Compiler). 1970.Nagel's encyclopedia-guide. The moon. (Transl. fromGerman by Jutta M.Fielden, Geneva, Switzerland.GUEST, JOHN (Editor). 1971. The earth and its satellite.David McKay Company, New York.HAMMOND, ALLENL. 1972. Lunar research; no agreementon evolutionary models. Science 175:868-870.HINNERS, N. W. 1971. The new moon; a view. Revs.Geophys. Space Phys. 9:447-552.LEVINSON, ALFRED A., and S ROSS TAYLOR. 1971.Moon rocks and minerals. Pergamon Press.MASON, BRIAN, and WILLIAMMELLSON. 1970. Thelunar rocks. Wiley-Interscience, New York.MUTCH, THOMAS A. 1970. Geology ofthe moon. PrincetonUniv. Press.12Journal of the Arkansas Academy of Science, Vol. 26 [1972], Art. 5https://scholarworks.uark.edu/jaas/vol26/iss1/5

Moon, Then and Now

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 26 Article 51972Moon, Then and NowKirtley F. MatherHarvard UniversityFollow this and additional works at: http://scholarworks.uark.edu/jaasThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationMather, Kirtley F. (1972) "Moon, Then and Now," Journal of the Arkansas Academy of Science: Vol. 26 , Article 5.Available at: http://scholarworks.uark.edu/jaas/vol26/iss1/5Arkansas Academy of Science Proceedings, Vol. XXVI,1972 11The Moon, Then and NowKIRTLEYF.MATHERProfessor of Geology, Emeritus, Harvard University, Cambridge, Massachusetts*FOREWORDDr. Mather wrote this article on the state ofmoon research in honor of the University ofArkansas Centennial Celebration and the specialexhibition of lunar material at the UniversityMuseum in connection with the 1972 meeting ofthe Arkansas Academy of Science at Fayetteville.The paper was written at the express request of Dr.Samuel C. Dellinger, Emeritus Professor ofZoology and former curator of the Museum at theUniversity of Arkansas. Dr. Mather taught geologyat the University of Arkansas from 1911 to 1914,and later was professor of geology at HarvardUniversity for nearly 30 years. He was awarded hisPh.D from the University of Chicago, wasassociated with the U.S. Geological Survey fornearly 35 years, and has received a number ofhonorary degrees. He has been a member andofficer of numerous professional organizations,and is a past president of the AmericanAssociation for the Advancement of Science. Dr.Mather is a prolificauthor, having produced manytechnical and popular works in the fields ofgeology, physiography, and education over thepast half century.The moon has changed scarcely at all since the University ofArkansas was founded in 1871 ,but our knowledge about it hasncreased by several orders ofmagnitude, most spectacularly asresult of the "moon walks" performed by Apollo astronautsince 20 July 1969. Anyone interested in selenology - the>eology ofthe moon -- cannot but be thrilled by even the mostasual inspection of the samples of the moon's surfacematerials that they brought back to earth.IThis is not to say, however, that not much was known aboute moon ahundred years ago. Using his home-made telescope,Galileo (1564-1642) had published sketches of the moon'ssurface in 1609 showing several ofits largest craters, mountainranges, and irregularly circular plains. Those plains weredesignated as "maria" by Riccioli (1598-1671) in his notable"book about the moon," published in 1651. Init he named aarge number of the craters for famous scientists and)hilosophers, and gave highly imaginative names to many oflemaria. The majority ofRiccioli's names are still used todaynd some of them are now familiar to millions of people as aesult of coverage of the exploits of the Apollo crews by theews media; for example, Mare Tranquillitatis (the Sea ofranquillity), Mare Imbrium (the Imbrium Basin), and theraters named Copernicus and Archimedes.tLikewise, the 16th to 18th century astronomers hadmputed with increasing accuracy the size, mass, and averageecific gravity ofthe moon and its tidal effects on the earth asrevolved around our planet. The years since 1871 havetnessed only somewhat greater precision of measurementsncerning those bits of information. On the other hand,completely new instruments and techniques for observation ofPresent address: 1044 Stanford Drive. NEAlbuquerque, NM 87106such a remote object have been invented during those years andespecially during the last 10 or 15 of them. Combining theseinventions with the new physics and chemistry of "the atomicage" and the techniques of space transportation developed inthe even newer "space age," modern science and technologyhave given us an amazing amount of information about themoon.The colossal task of analyzing, correlating, and interpretingthe vast store of factual data now available is proceeding inhundreds of scientific laboratories around the world, but it hasbyno means been completed. Some important questions aboutthe moon and its history still remain unanswered. Even so, thewild, free-wheeling speculations, rampant a century or moreago, are now replaced by a few carefully restricted workinghypotheses, and a number ofsignificant generalizations may bestated with great confidence.The moon is composed ofrocks and minerals nearly the sameas rocks and minerals found here on earth. It came intoexistence approximately 4.6 billion years ago, at the same timeas the earth. Most selenologists consider that itwas formed byaccretion of planetesimals orbiting the growing earth andothers orbiting the sun. During the first 1.5 billion years ofitshistory, its thermal processes and internal activity wereprobably quite similar to those of the juvenile earth. Since then,unlike the earth, itapparently has been a slowly cooling bodylacking any significant deep-seated internal activity.Furthermore, because ofits small size, the moon has never hadsufficient gravitational force to retain an atmosphere andhydrosphere that could engender processes of erosion andsedimentation like those that have played an important role inthe evolution of the earth.Evidence from three seismometers (instruments that measuremoonquakes in the same way as earthquakes) left on themoon's surface by Apollo astronauts indicates that the moonhas a layered crust approximately 65 km (about 40 mi) thick,and there is some suggestion from the remanentpaleomagnetism detected in "moon rocks" that the moon hasan iron core which was molten during its infancy. Ifso, thatcore cannot have a radius greater than 0.2 the radius of themoon and it is therefore relatively much smaller than theearth's core. However, there is nothing to indicate that theinternal structure ofthe moon comprises a convective mantleresembling dynamically that portion of the earth between itscore and crust.Samples of the moon's surface materials from five ratherwidely scattered sites now have been studied directly here onearth. The specimens from one of the five localities werescooped up and retrieved by the unmanned USSR Luna 16spacecraft; the others were collected by the crews of Apollo11,12, 14, and 15. The petrologists report that the specimens theyhave studied represent three major types ofrock and fragmentsderived from them. The oldest are rather coarsely crystallizedigneous rocks, such as anorthosite, composed largely ofplagioclase feldspar, that were formed by comparatively slowcrystallization from fairly large bodies ofmolten magma about4 billion years ago. They are characteristic of the moon'shighlands and include David Scott's "genesis rock" (identified11Journal of the Arkansas Academy of Science, Vol. 26 [1972], Art. 5Published by Arkansas Academy of Science, 1972Iii12 Arkansas Academy of Science Proceedings, Vol.XXVI,1972IKirtleyF.Matherby Scott as anorthosite while he was on the moon during theApollo 15 mission; the designation "genesis rock" waspromptly coined by a reporter in Houston and has since beenwidely used). They come as close to representing thecomponents ofthe original lunar surface as we are likely to get.Intermediate in age is a basaltic type of fine-grained igneousrock, notably rich inpotassium (symbol K),rare earth elements(symbol REE), and phosphorus (symbol P), and hence called"KREEP basalt." Many fragments of this kind of basalt werescattered around by the impact ofincoming meteorites, most ofwhich were much smaller than the huge projectile responsiblefor forming the Imbrium Basin, just beyond the rim of whichApollo 15 landed. The third major type of rock consists of>asalts much more similar to those at many places on theearth's surface; they are sometimes referred to as "normal>asalts" in contrast to the older "KREEP basalts." Allof theocks thus far dated by radioactive methods are between 3.1and 3.7 billion years old. They occur characteristically as lavalows that flooded pre-existing basins -most, ifnot all of whichwere formed by impacting meteorites - to produce the existingmaria.Fragments of these ancient rocks were scattered by theexplosive impact of meteorites bombarding the face of themoon during the last 3 billion years, in general in decreasingnumbers as the millenia went by. In some places theirdistribution is in a pattern of rays, radiating from craters likeCopernicus. In many places where they accumulated to aconsiderable thickness, the fragments form breccias, solidifieday compaction under the weight of the overburden or bycementation by shock-melted glass. Some of the loosefragments in the rock collections are glazed on one or moresides by such glass. This material is particularly abundant inthe "fines" of the lunar samples.Ingeneral the relative age of the craters that pockmark themoon's surface can be inferred from the extent of rounding orsoftening of their originally sharp peripheral rims. Rocks areFractured and shattered by expansion and contraction due tohe great changes in surface temperature between the excessiveleat of the long days and the deep freeze of the long nightseach equal in length to 14 earth days). Gravity pulls theloosened particles down slope, even though its force on themoon is about one-fifth of its force at the surface of the earth.Lunar talus slopes and cones are similar to analogousandforms on earth. The impact of micrometeorites may movedust particles fromplace to place inmuch the same way as theyare moved about by terrestrial breezes. Almost everywhere thesolid rock of the lunar crust is veneered with lunar "soil" --jetter designated as regolith -- from a few centimeters to manymeters thick. Fortunately the loose particles of the lunarregolith are compacted rapidly under their own weight so that'moon walkers" and their vehicles leave footprints and tracksbut do not sink far into the regolith.The overwhelming majority ofthe lunar craters were formedby impact ofmeteorites or planetesimals; they are definitely notofvolcanic origin. Infact, outpouring oflava and other kinds ofvolcanic activity seem to have ceased, for all practical purposes,some 3 billion years ago. Even so, there is still a slightpossibility that some volcanic cones and /or craters may yet beidentified as exploration ofthe moon continues, and that recentor even currently active volcanism may be detected somewhereon its surface. The report from the Soviet Union that anemission ofgas from the crater Alphonsus was observed in1958should not be totally discarded as an aberration of instrumentsor men, even though that observation has never been confirmedor repeated elsewhere.The age-old question as to whether there is life on the moon,even though itmight be some kind of livingcreature whollydifferent from any known on earth, has now been answeredquite definitely in the negative. According to N.W. Hinners(1971, p. 448): "...no life forms have been found, nor haveorganic molecules been unambiguously identified as beingindigenous to the moon. The virtually complete lack of waterand the four-plus billion years of exposure to a harsh spaceenvironment make eventual detection of lunar life unlikely."ACKNOWLEDGMENTSThe writer thanks Dr. Klaus Keil, Director ofthe Institute of Meteoritics, University of NewMexico, for supplying helpful documents andreading critically the first draft of this article. Thewriter, however, is solely responsible for itscontents, including any inadvertent errors it maycontain.REFERENCESAPOLLO 15PRELIMINARYEXAMINATIONTEAM. 1972.The Apollo 15 lunar samples: a preliminary description.Science 175:363-375.BAUMGARTEN, PETER (Editor and Compiler). 1970.Nagel's encyclopedia-guide. The moon. (Transl. fromGerman by Jutta M.Fielden, Geneva, Switzerland.GUEST, JOHN (Editor). 1971. The earth and its satellite.David McKay Company, New York.HAMMOND, ALLENL. 1972. Lunar research; no agreementon evolutionary models. Science 175:868-870.HINNERS, N. W. 1971. The new moon; a view. Revs.Geophys. Space Phys. 9:447-552.LEVINSON, ALFRED A., and S ROSS TAYLOR. 1971.Moon rocks and minerals. Pergamon Press.MASON, BRIAN, and WILLIAMMELLSON. 1970. Thelunar rocks. Wiley-Interscience, New York.MUTCH, THOMAS A. 1970. Geology ofthe moon. PrincetonUniv. Press.12Journal of the Arkansas Academy of Science, Vol. 26 [1972], Art. 5http://scholarworks.uark.edu/jaas/vol26/iss1/5

https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2931&amp;context=jaas

Moon, Then and Now

Abstract

Similar works

Full text

Available Versions

UARK (University of Arkansas )

ScholarWorks@UARK