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Origin of the earth and moon
BOOK REVIEWS
Rambler, L. Margulis and E. Barghoorn (Natural mechanisms of protection of a blue-green alga against ultraviolet light). and C. Folsome (Synthetic organic microstructures as model systems of early protobionts). In general the editor seems to have taken care to ensure that each paper follows a standard format. Although attractively produced the photographs are of a poor quality as are a number of the line drawings. There exists some duplication of references (i.e. the Barghoorn and Tyler, 1965 paper is found in six different lists) which may have been avoided if there had been just one listing. In the preface the editor indicates that “The latest information available on this subject was critically examined. .“, however, it should be pointed out that some degree of provincialism is evident. Of the 33 participating scientists 22 were from the United States and 7 from Great Britain. A summary paper outlining the general conclusions of the meeting would have been a valuable addition. These minor Raws, however. should not detract from the obvious value of this volume. It is indeed rare to find an informative, reasonably priced book on so fascinating a topic, It should be on the shelf of every scientist who has an interest in keeping up with the latest information regarding the question “How did life begln’!”
Chemical Evolution of the Early Precambrian, edited by PONNAMPERUMA. Academic Press, 1977, 221 pp. $I 5.00 (Hard cover). CYRIL
“How DID LIFE BEGIN'? is one of the most puzzling questions facing science today, and one that is bound to generate considerable debate. This question was one of the major concerns of the Second College Park Colloquium on Chemical Evolution held in late 1975 at the University of Maryland. Thirty-three of the worlds leading authorities gathered to present a series of papers dealing with virtually every aspect of the chemical evolution of the early Precambrian. These papers have been organized and edited by Cyril Ponnamperuma and represent the latest thinking on the subject. PIlthough the organization of the book appears haphazard the 22 individual contributions can be grouped into three broad areas: papers dealing with the physical characteristics of Precambrian rocks and the evolution of the atmosphere: the significance and distribution of individual chemical groups; and finally papers dealing with specific types of Precambrian organisms. Because of space limitations. it is not possible to review each individual contribution. Most are well written and all are informative and deserve attention. Of particular interest are the contributions by R. Siever (Early Precambrian weathering and sedimentation: an impressionistic view), C. B. Moore and D. Welch (Carbon contents of early Precambrian Rocks), M.
Origin of the Earth and Moon, by Springer -Veriag, 1979. 295 pp. 324.80.
A. E. RINGWOOD.
Trr~ IMPORTANCE of the question addressed by this book hardly needs to be argued. Nor does the stature of A. E. Ringwood of the Australian National tlniversity, Canberra, who has published thoughtful and imaginative papers on this topic for two decades. Ringwood’s perception of the pertinent data and the planet-forming processes thev seem to call for evolve with time: the book under review represents the most recent summing-up of his views. It is divided into three parts. The first, “Composition and Constitution of the Earth,” contains descriptive chapters on the gross structure and the geochemistry of Earth, with some emphasis on those properties that lead to the interpretations in chapters to come; a chapter on the core. with Ringwood’s current view of its composition; and a summary chapter marshalling the boundary conditions, as the author sees them, for the origin of the earth. The second section, “Origin of the Earth”, contains two chapters that competently review astronomical and cosmochemical thinking about the origin of the solar system and the planets generally. Two more chapters set forth Ringwood’s own past and present thought about the origin of the earth in particular. The third section, “The Moon and Planets,” contains a chapter that reviews the properties of the other terrestrial planets. and applies the model developed by the author in the last section to them individually; a chapter reviewing the constitution and composition of the moon; one setting forth in detail the geochemical regularities that Ringwood considers the key to an understanding of the moon; and a
final chapter containing his model for the origin of the moon. It should be stressed that this book is not a review of the subject of planetary origin. It is an exposition of one man’s thinking on the subject, with enough discussion of other alternatives to place the problem in context and allow Ringwood to argue the superiority of his views. Readers familiar with the field will find (and will expect to find) much of it controversial. Major concepts that will not meet with universal agreement are: (1) The earth’s mantle is essentially uniform in chemical composition from top to bottom, and significantly depleted in Si relative to chondritic meteorites (Si.‘Mg - 0.84 x cosmic). (2) The light element in Earth’s core is principally 0. not S, Si, or C. (3) Earth’s mantle was not melted during accretion or core formation. [If it had been, Ringwood argues. it would have differentiated subsequently into a Skaergaard-like sequence, which (1) above rules out.] Core-formation proceeded via melting and segregation of eutectic proportions of Fe and Fe0 in the mantle, coupled with vigorous solidstate convection of the mantle. The phase relations applicable to this situation are somewhat speculative. (4) The terrestrial planets are compounded large11 of mixtures of two basic pre-planetary components. Component A has the cosmic proportions of elements, including the full complement of volatiles; it was quite slmllar to Cl carbonaceous chondrites. The other and more abundant component (B) was depleted in volatiles (including Si; this accounts for the Si deficiency of Earth’s mantle). Its Fe was fully reduced. Variations in the proportions of these two components account for most of the differences in the ma-
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Book reviews
terial properties of Earth, Venus and Mars. Component B does not correspond to a known class or component of chondritic meteorites. Ringwood does not believe the raw materials of the terrestrial planets were necessarily very similar to chondrites. (5) Close similarities in the inferred compositions (especially siderophile trace element abundances) of the mantles of Earth and Moon require that the moon was once part of the earth. (6) The moon was probably formed by the glancing collision of a major planetesimal with Earth, ejecting terrestrial mantle material which later reconstituted itself into the moon. Details of the process are not specified. Items (3), (4) and (6) constitute a major departure from Ringwood’s earlier view, which was that Earth was not only melted but boiled and distilled by the energy of accretlon and core formation; the distillation of volatile Si was responsible for the Si depletion of the residual mantle. Condensation and re-accretion of distilled vapors spun off from the earth produced the moon. It might reasonably be asked if the publication of a whole book is justified to air the opinions of one scientist. In some cases even a journal article seems a questionable use of our forest resources. In the present instance the answer has to be yes. It is hard to think of any other single
worker in the field whose expertise across the disciplines of geochemistry, geophysics, and petrology makes him more qualified to address the problem than Ringwood. A book instead of a journal article is required to explain Ringwood’s position because he has followed up, in scholarly detail, so many of the essential ramifications of an obviously complicated problem. This makes “Origin of the Earth and Moon” sound intimidating. but in fact it is clearly and lucidly written, well-produced, remarkably free of typographical errors, and highly readable. On top of this, its price is surprisingly moderate for this day and age. A person interested in this field cannot afford to ignore Ringwood’s book. He may disagree with some of the author’s conclusions, but should study carefully the data he argues from and the constraints and boundary conditions he derives. I don’t think, however, I would recommend the book as a classroom text. Not unless the teacher is prepared to keep a cabinet of strong antidotes close at hand, and dose his students with them frequently.
Haward-Smithsonian Center for Astrophysics 60 Garden Street Cambridge, MA 0213X. U.S.A.
J. A. Wool
Rambler, L. Margulis and E. Barghoorn (Natural mechanisms of protection of a blue-green alga against ultraviolet light). and C. Folsome (Synthetic organic microstructures as model systems of early protobionts). In general the editor seems to have taken care to ensure that each paper follows a standard format. Although attractively produced the photographs are of a poor quality as are a number of the line drawings. There exists some duplication of references (i.e. the Barghoorn and Tyler, 1965 paper is found in six different lists) which may have been avoided if there had been just one listing. In the preface the editor indicates that “The latest information available on this subject was critically examined. .“, however, it should be pointed out that some degree of provincialism is evident. Of the 33 participating scientists 22 were from the United States and 7 from Great Britain. A summary paper outlining the general conclusions of the meeting would have been a valuable addition. These minor Raws, however. should not detract from the obvious value of this volume. It is indeed rare to find an informative, reasonably priced book on so fascinating a topic, It should be on the shelf of every scientist who has an interest in keeping up with the latest information regarding the question “How did life begln’!”
Chemical Evolution of the Early Precambrian, edited by PONNAMPERUMA. Academic Press, 1977, 221 pp. $I 5.00 (Hard cover). CYRIL
“How DID LIFE BEGIN'? is one of the most puzzling questions facing science today, and one that is bound to generate considerable debate. This question was one of the major concerns of the Second College Park Colloquium on Chemical Evolution held in late 1975 at the University of Maryland. Thirty-three of the worlds leading authorities gathered to present a series of papers dealing with virtually every aspect of the chemical evolution of the early Precambrian. These papers have been organized and edited by Cyril Ponnamperuma and represent the latest thinking on the subject. PIlthough the organization of the book appears haphazard the 22 individual contributions can be grouped into three broad areas: papers dealing with the physical characteristics of Precambrian rocks and the evolution of the atmosphere: the significance and distribution of individual chemical groups; and finally papers dealing with specific types of Precambrian organisms. Because of space limitations. it is not possible to review each individual contribution. Most are well written and all are informative and deserve attention. Of particular interest are the contributions by R. Siever (Early Precambrian weathering and sedimentation: an impressionistic view), C. B. Moore and D. Welch (Carbon contents of early Precambrian Rocks), M.
Origin of the Earth and Moon, by Springer -Veriag, 1979. 295 pp. 324.80.
A. E. RINGWOOD.
Trr~ IMPORTANCE of the question addressed by this book hardly needs to be argued. Nor does the stature of A. E. Ringwood of the Australian National tlniversity, Canberra, who has published thoughtful and imaginative papers on this topic for two decades. Ringwood’s perception of the pertinent data and the planet-forming processes thev seem to call for evolve with time: the book under review represents the most recent summing-up of his views. It is divided into three parts. The first, “Composition and Constitution of the Earth,” contains descriptive chapters on the gross structure and the geochemistry of Earth, with some emphasis on those properties that lead to the interpretations in chapters to come; a chapter on the core. with Ringwood’s current view of its composition; and a summary chapter marshalling the boundary conditions, as the author sees them, for the origin of the earth. The second section, “Origin of the Earth”, contains two chapters that competently review astronomical and cosmochemical thinking about the origin of the solar system and the planets generally. Two more chapters set forth Ringwood’s own past and present thought about the origin of the earth in particular. The third section, “The Moon and Planets,” contains a chapter that reviews the properties of the other terrestrial planets. and applies the model developed by the author in the last section to them individually; a chapter reviewing the constitution and composition of the moon; one setting forth in detail the geochemical regularities that Ringwood considers the key to an understanding of the moon; and a
final chapter containing his model for the origin of the moon. It should be stressed that this book is not a review of the subject of planetary origin. It is an exposition of one man’s thinking on the subject, with enough discussion of other alternatives to place the problem in context and allow Ringwood to argue the superiority of his views. Readers familiar with the field will find (and will expect to find) much of it controversial. Major concepts that will not meet with universal agreement are: (1) The earth’s mantle is essentially uniform in chemical composition from top to bottom, and significantly depleted in Si relative to chondritic meteorites (Si.‘Mg - 0.84 x cosmic). (2) The light element in Earth’s core is principally 0. not S, Si, or C. (3) Earth’s mantle was not melted during accretion or core formation. [If it had been, Ringwood argues. it would have differentiated subsequently into a Skaergaard-like sequence, which (1) above rules out.] Core-formation proceeded via melting and segregation of eutectic proportions of Fe and Fe0 in the mantle, coupled with vigorous solidstate convection of the mantle. The phase relations applicable to this situation are somewhat speculative. (4) The terrestrial planets are compounded large11 of mixtures of two basic pre-planetary components. Component A has the cosmic proportions of elements, including the full complement of volatiles; it was quite slmllar to Cl carbonaceous chondrites. The other and more abundant component (B) was depleted in volatiles (including Si; this accounts for the Si deficiency of Earth’s mantle). Its Fe was fully reduced. Variations in the proportions of these two components account for most of the differences in the ma-
1621
1622
Book reviews
terial properties of Earth, Venus and Mars. Component B does not correspond to a known class or component of chondritic meteorites. Ringwood does not believe the raw materials of the terrestrial planets were necessarily very similar to chondrites. (5) Close similarities in the inferred compositions (especially siderophile trace element abundances) of the mantles of Earth and Moon require that the moon was once part of the earth. (6) The moon was probably formed by the glancing collision of a major planetesimal with Earth, ejecting terrestrial mantle material which later reconstituted itself into the moon. Details of the process are not specified. Items (3), (4) and (6) constitute a major departure from Ringwood’s earlier view, which was that Earth was not only melted but boiled and distilled by the energy of accretlon and core formation; the distillation of volatile Si was responsible for the Si depletion of the residual mantle. Condensation and re-accretion of distilled vapors spun off from the earth produced the moon. It might reasonably be asked if the publication of a whole book is justified to air the opinions of one scientist. In some cases even a journal article seems a questionable use of our forest resources. In the present instance the answer has to be yes. It is hard to think of any other single
worker in the field whose expertise across the disciplines of geochemistry, geophysics, and petrology makes him more qualified to address the problem than Ringwood. A book instead of a journal article is required to explain Ringwood’s position because he has followed up, in scholarly detail, so many of the essential ramifications of an obviously complicated problem. This makes “Origin of the Earth and Moon” sound intimidating. but in fact it is clearly and lucidly written, well-produced, remarkably free of typographical errors, and highly readable. On top of this, its price is surprisingly moderate for this day and age. A person interested in this field cannot afford to ignore Ringwood’s book. He may disagree with some of the author’s conclusions, but should study carefully the data he argues from and the constraints and boundary conditions he derives. I don’t think, however, I would recommend the book as a classroom text. Not unless the teacher is prepared to keep a cabinet of strong antidotes close at hand, and dose his students with them frequently.
Haward-Smithsonian Center for Astrophysics 60 Garden Street Cambridge, MA 0213X. U.S.A.
J. A. Wool