Chemical composition and accretion history of terrestrial planets

1988 ◽  
Vol 325 (1587) ◽  
pp. 545-557 ◽  
Keyword(s):  
Bulk Composition ◽  
Parent Body ◽  
Conclusive Evidence ◽  
Martian Surface ◽  
Volatile Elements ◽  
The Earth ◽  
Material Component ◽  
History Of ◽  
Siderophile Elements ◽  
High Concentrations

The high concentrations of moderately siderophile elements (Ni, Co, etc.) in the Earth’s mantle and the similarity of their Cl normalized abundances to those of moderately volatile elements (F, Na, K, Rb) and some elements such as In, which under solar nebula conditions are highly volatile, are striking. To account for the observed abundances, inhomogeneous accretion of the Earth from two components has been proposed. In this model accretion started with the highly reduced component A devoid of all elements more volatile than Na, followed by accretion of more and more oxidized material (component B), containing all elements in Cl abundances. Recent observations have brought almost conclusive evidence that SNC meteorites are martian surface rocks ejected by huge impacts. By assuming that Mars is indeed the parent body of SNC meteorites, the bulk composition of Mars is estimated. The data on the composition of Mars obtained in this way clearly show that the two-component model is also valid for Mars. The striking depletion of all elements with chalcophile character in the martian mantle indicates that, contrary to the Earth, Mars accreted almost homogeneously (H. Wanke, Phil. Trans. R. Soc. Lond . A 303, 287 (1981)).

Constitution of terrestrial planets

1981 ◽  
Vol 303 (1477) ◽  
pp. 287-302 ◽  
Keyword(s):  
Bulk Composition ◽  
Parent Body ◽  
The Moon ◽  
Volatile Elements ◽  
Earth’S Mantle ◽  
The Earth ◽  
History Of ◽  
Relationship Of ◽  
Reduced State

Reliable estimates of the bulk composition are so far restricted to the three planetary objects from which we have samples for laboratory investigation, i.e. the Earth, the Moon and the eucrite parent asteroid. The last, the parent body of the eucrite— diogenite family of meteorites, an object that like Earth and Moon underwent magmatic differentiations, seems to have an almost chondritic composition except for a considerable depletion of all moderately volatile (Na, K, Rb, F, etc.) and highly volatile (Cl, Br, Cd, Pb, etc.) elements. The Moon is also depleted in moderately volatile and volatile elements compared to carbonaceous chondrites of type 1 (Cl) and also compared to the Earth. Again normalized to Cl and Si the Earth’s mantle and the Moon are slightly enriched in refractory lithophile elements and in magnesium. It might be that this enrichment is fictitious and only due to the normalization to Si and that both Earth’s mantle and Moon are depleted in Si, which partly entered the Earth’s core in metallic form. The striking depletion of the Earth’s mantle for the elements V, Cr and Mn can also be explained by their partial removal into the core. The similar abundances of V, Cr and Mn in the Moon and in the Earth’s mantle indicate the strong genetic relationship of Earth and Moon. Apart from their contents of metallic iron, all siderophile elements, moderately volatile and volatile elements, Earth and Moon are chemically very similar. It might well be that, with these exceptions and that of a varying degree of oxidation, all the inner planets have a similar chemistry. The chemical composition of the Earth’s mantle, for which reliable and accurate data have recently been obtained from the study of ultramafic nodules, yields important information about the accretion history of the Earth and that of the inner planets. It seems that accretion started with highly reduced material, with all Fe as metal and even Si and Cr, V and Mn partly in reduced state, followed by the accretion of more and more oxidized matter.

Chemistry and accretion history of Mars

1994 ◽  
Vol 349 (1690) ◽  
pp. 285-293 ◽  
Keyword(s):  
Bulk Composition ◽  
Volcanic Gases ◽  
Martian Surface ◽  
Volatile Elements ◽  
Water Ice ◽  
The Earth ◽  
History Of ◽  
The Mean ◽  
Wet Climate ◽  
Martian Regolith

Using element correlations observed in SNC meteorites and general cosmochemical constraints, Wänke & Dreibus (1988) have estimated the bulk composition of Mars. The mean abundance value for moderately volatile elements Na, P, K, F, and Rb and most of the volatile elements like Cl, Br, and I in the Martian mantle exceed the terrestrial values by about a factor of two. The striking depletion of all elements with chalcophile character (Cu, Co, Ni, etc.) indicates that Mars, contrary to the Earth, accreted homogeneously, which also explains the obvious low abundance of water and carbon. SNC meteorites and especially the shergottites are very dry rocks, they also contain very little carbon, while the concentrations of chlorine and especially sulphur are higher than those in terrestrial rocks. As a consequence we should expect SO 2 and HC1 to be the most abundant compounds in Martian volcanic gases. This might explain the dominance of sulphur and chlorine in the Viking soils. In turn SO 2 , being an excellent greenhouse gas, may have been of major importance for the warm and wet period in the ancient Martian history. Episodic release of larger quantities of SO 2 stored in liquid or solid SO 2 tables in the Martian regolith triggered by volcanic intrusions as suggested here could lead to a large number of warm and wet climate periods of the order of a hundred years, interrupted by much longer cold periods characterized by water ice and liquid of solid SO 2 . Sulphur (FeS) probably also governs the oxygen fugacity of the Martian surface rocks.

The Projectile of the Lappajärvi Impact Crater

1980 ◽  
Vol 35 (2) ◽  
pp. 197-203 ◽  
Author(s):  
Elke Göbel ◽  
Uwe Reimold ◽  
Hildegard Baddenhausen ◽  
Herbert Palme
Keyword(s):  
Impact Crater ◽  
Carbonaceous Chondrite ◽  
Volatile Elements ◽  
Rich Phase ◽  
Impact Melt ◽  
Siderophile Elements ◽  
High Concentrations ◽  
Impact Melts

Abstract Two impact melt samples from the Lappajärvi crater (Scandinavia) are highly enriched in siderophile elements, such as Ir, Re, and Os. This indicates the presence of a meteoritic component. The simultaneous enrichments of Ni, Co, Cr, and Se suggest a chondritic projectile. Because of the relatively large indigenous contributions to Ni, Co, and Cr, it is not possible to distinguish between a normal and a carbonaceous chondrite. The high concentrations of relatively volatile elements could point towards a volatile-rich projectile.The two melt samples have high Re/Ir ratios compared to chondritic ratios. Enrichment of Re relative to Ir is very unusual in terrestrial impact melts. Loss of Re, because of volatilisation under oxidizing conditions or by weathering is frequently observed.The high Re/Ir ratios and the high abundances of relatively volatile elements either indicate the presence of a volatile rich phase or they characterize a type of meteorite, which has not been sampled. Some lunar highland rocks have a pattern of meteoritic elements rather similar to that observed for the Lappajärvi meteorite.The Lappajärvi crater is, after Rocheehouart, the second European crater where a significant amount of meteoritic component has been found.A melt sample from the Lake St. Martin crater (Manitoba), did not show any enrichment in meteoritic elements.

scholarly journals Evaporative fractionation of volatile stable isotopes and their bearing on the origin of the Moon

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130259 ◽  
Author(s):  
James M. D. Day ◽  
Frederic Moynier
Keyword(s):  
Global Scale ◽  
Parent Body ◽  
The Moon ◽  
Magma Ocean ◽  
Volatile Elements ◽  
Giant Impact ◽  
The Earth ◽  
Present Distribution ◽  
Volatile Loss

The Moon is depleted in volatile elements relative to the Earth and Mars. Low abundances of volatile elements, fractionated stable isotope ratios of S, Cl, K and Zn, high μ ( 238 U/ 204 Pb) and long-term Rb/Sr depletion are distinguishing features of the Moon, relative to the Earth. These geochemical characteristics indicate both inheritance of volatile-depleted materials that formed the Moon and planets and subsequent evaporative loss of volatile elements that occurred during lunar formation and differentiation. Models of volatile loss through localized eruptive degassing are not consistent with the available S, Cl, Zn and K isotopes and abundance data for the Moon. The most probable cause of volatile depletion is global-scale evaporation resulting from a giant impact or a magma ocean phase where inefficient volatile loss during magmatic convection led to the present distribution of volatile elements within mantle and crustal reservoirs. Problems exist for models of planetary volatile depletion following giant impact. Most critically, in this model, the volatile loss requires preferential delivery and retention of late-accreted volatiles to the Earth compared with the Moon. Different proportions of late-accreted mass are computed to explain present-day distributions of volatile and moderately volatile elements (e.g. Pb, Zn; 5 to >10%) relative to highly siderophile elements (approx. 0.5%) for the Earth. Models of early magma ocean phases may be more effective in explaining the volatile loss. Basaltic materials (e.g. eucrites and angrites) from highly differentiated airless asteroids are volatile-depleted, like the Moon, whereas the Earth and Mars have proportionally greater volatile contents. Parent-body size and the existence of early atmospheres are therefore likely to represent fundamental controls on planetary volatile retention or loss.

Nickel for Your Thoughts: Urey and the Origin of the Moon

Science ◽  
1982 ◽  
Vol 217 (4563) ◽  
pp. 891-898 ◽  
Author(s):  
Stephen G. Brush
Keyword(s):  
Solar System ◽  
The Moon ◽  
Lunar Crust ◽  
Lunar Landing ◽  
The Earth ◽  
History Of ◽  
Siderophile Elements ◽  
Origin Of The Moon ◽  
Manned Lunar Landing

The theories of Harold C. Urey (1893-1981) on the origin of the moon are discussed in relation to earlier ideas, especially George Howard Darwin's fission hypothesis. Urey's espousal of the idea that the moon had been captured by the earth and has preserved information about the earliest history of the solar system led him to advocate a manned lunar landing. Results from the Apollo missions, in particular the deficiency of siderophile elements in the lunar crust, led him to abandon the capture selenogony and tentatively adopt the fission hypothesis.

Comparative chemical history of the Earth, the Moon and parent body of achondrite

1977 ◽  
Vol 285 (1327) ◽  
pp. 55-67 ◽  
Keyword(s):  
Major Elements ◽  
Parent Body ◽  
Chemical Fractionation ◽  
The Moon ◽  
Molten Layer ◽  
The Earth ◽  
Lunar Samples ◽  
History Of ◽  
Chemical History ◽  
Major Chemical

Chronological studies on the lunar samples suggest that major chemical fractionation occurred at 4.4 Ga. It is inferred from both whole-rock Rb-Sr isochron and Nd-Sm systematics. It is stressed that any models on the lunar petrogenesis and evolution should reconcile with this early fractionation. A model for chemical evolution of the Moon (extensive fractional crystallization of a molten layer, followed by impact melting and mixing of melts) is discussed to account for phase relations and r.e.e. abundances. Similar chronological characteristics are observed for achondrite parent body. Achondrite parent body experienced a similar evolutionary history to the Moon starting with a slightly different initial composition (major elements). In the Earth, on the contrary, chemical differentiation has continued (or is still continuing) as indicated by chronological and isotopic evidence.

The Bulk Composition of the Eucrite Parent Asteroid and its Bearing on Planetary Evolution

1980 ◽  
Vol 35 (2) ◽  
pp. 204-216 ◽  
Author(s):  
Gerlind Dreibus ◽  
Heinrich Wänke
Keyword(s):  
Genetic Relationship ◽  
Bulk Composition ◽  
Building Blocks ◽  
Parent Body ◽  
Strong Indication ◽  
Volatile Elements ◽  
Planetary Evolution ◽  
Incompatible Elements ◽  
Relationship Of ◽  
Binary Mixing

Abstract It is shown that howardites fit extraordinary well into a binary mixing diagram for both their major and trace element compositions. Eucrites and diogenites would be suitable endmembers. In the mixing diagram computed from the elemental compositions of howardites, we find at a certain position a composition with very special features. This composition designated PR* contains all refractory incompatible elements in almost C 1, i.e. primitive, abundances. If 43% olivine is added to PR* in order to match the C 1 value for the Mg/Si ratio, a composition is obtained which has almost exact C 1 abundance values for all lithophile elements of non-volatile character. Because of its probable genetic relation we have used an olivine composition equal to that of pallasites. An eucrite parent body (EPB) with eucrites, diogenites and pallasites as the major building blocks has been previously suggested by various authors.The bulk composition of the EPB, resulting from our computations is found to be almost chondritic, but with a considerable depletion of volatile and moderately volatile elements. A comparison of the bulk composition of the EPB with that of Earth and Moon reveals a number of remarkable differences. Thus, the similarity of the composition of the silicate phases of Earth and Moon becomes even more remarkable and must be taken as strong indication for the genetic relationship of Earth and Moon.

George Hoggart Toulmin: politics and geology

1978 ◽  
Vol 8 (4) ◽  
pp. 481-481
Author(s):  
ROY PORTER
Keyword(s):  
French Revolution ◽  
Social Order ◽  
Lower Class ◽  
Great Distance ◽  
The Earth ◽  
Christian View ◽  
The Social ◽  
French Enlightenment ◽  
Political Conservatism ◽  
History Of

The physician George Hoggart Toulmin (1754–1817) propounded his theory of the Earth in a number of works beginning with The antiquity and duration of the world (1780) and ending with his The eternity of the universe (1789). It bore many resemblances to James Hutton's "Theory of the Earth" (1788) in stressing the uniformity of Nature, the gradual destruction and recreation of the continents and the unfathomable age of the Earth. In Toulmin's view, the progress of the proper theory of the Earth and of political advancement were inseparable from each other. For he analysed the commonly accepted geological ideas of his day (which postulated that the Earth had been created at no great distance of time by God; that God had intervened in Earth history on occasions like the Deluge to punish man; and that all Nature had been fabricated by God to serve man) and argued they were symptomatic of a society trapped in ignorance and superstition, and held down by priestcraft and political tyranny. In this respect he shared the outlook of the more radical figures of the French Enlightenment such as Helvétius and the Baron d'Holbach. He believed that the advance of freedom and knowledge would bring about improved understanding of the history and nature of the Earth, as a consequence of which Man would better understand the terms of his own existence, and learn to live in peace, harmony and civilization. Yet Toulmin's hopes were tempered by his naturalistic view of the history of the Earth and of Man. For Time destroyed everything — continents and civilizations. The fundamental law of things was cyclicality not progress. This latent political conservatism and pessimism became explicit in Toulmin's volume of verse, Illustration of affection, published posthumously in 1819. In those poems he signalled his disapproval of the French Revolution and of Napoleonic imperialism. He now argued that all was for the best in the social order, and he abandoned his own earlier atheistic religious radicalism, now subscribing to a more Christian view of God. Toulmin's earlier geological views had run into considerable opposition from orthodox religious elements. They were largely ignored by the geological community in late eighteenth and early nineteenth century Britain, but were revived and reprinted by lower class radicals such as Richard Carlile. This paper is to be published in the American journal, The Journal for the History of Ideas in 1978 (in press).

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