The age of the Earth

Forty years ago, Patterson in his pioneering work on lead isotopes defined the age of the Earth and of the meteorites with 4.55 Ga. We reconsider the question of the age of the Earth and its relation to the age of the meteorites, and similar to Patterson's approach, we use lead isotope systematics. UPb investigations of three meteoritic objects on which early thermal and/or chemical events generated large U/Pb fractionations are outlined in this article: refractory inclusions of the Allende meteorite, phosphates in ordinary chondrites and basaltic achondrites. All these samples contain lead with highly radiogenic compositions (206Pb/204Pb > 150) and therefore their 207Pb206Pb age is almost independent of the isotopic composition associated with the measured 204Pb to within the precision of a few million years. The PbPb ages of the most radiogenic compositions measured in Allende refractory inclusions range from 4.568 to 4.565 Ga, the PbPb ages of secondary phosphates in equilibrated ordinary chondrites vary from 4.563 to 4.504 Ga, and basaltic achondrites show ages between 4.558 and 4.53 Ga. These age determinations indicate precise time constraints for the classical scenario concerning the formation of the first planetary objects of the solar system. Formation of the Allende refractory inclusions occurs at 4566+2/−1 Ma. Accretion of chondritic bodies occurred at a maximum of 3 Ma later. Eight million years after formation of the Allende inclusions, magmatic activity, including partial melting, magma segregation, and eruption occurs on planetary bodies. During the next 200 Ma thermal processing, shock perturbation, and heating takes place. The meaning of an “age of the Earth” is evaluated in relation to the major early processes, end of accretion, core formation, and atmosphere extraction. A similar value for the age of the Earth is found based on lead isotopes and IXe systematics; this age is about 0.1 Ga younger than that of primitive meteorites. PbPb and IXe terrestrial ages are interpreted as mean ages of core segregation and of atmosphere outgassing, respectively. Within this framework, the “age of the Earth” corresponds to the end of its accretion and to its early differentiation.

[1]  A. Provost,et al.  Topology in isotopic multispace and origin of mantle chemical heterogeneities , 1987 .

[2]  H. Wänke,et al.  Mantle Chemistry and Accretion History of the Earth , 1984 .

[3]  J. Minster,et al.  Absolute age of formation of chondrites studied by the 87Rb–87Sr method , 1982, Nature.

[4]  J. Gilluly,et al.  Principles of Geology , 1969 .

[5]  X. Kelvin.  THE AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. II. , 1899, Science.

[6]  B. Dupré,et al.  Lead-lead age of komatiitic lavas and limitations on the structure and evolution of the Precambrian mantle , 1986 .

[7]  T. Staudacher,et al.  Speculations about the cosmic origin of He and Ne in the interior of the Earth , 1993 .

[8]  G. Manhès,et al.  UThPb systematics of the eucrite "Juvinas": Precise age determination and evidence for exotic lead , 1984 .

[9]  E. Hubble.  A RELATION BETWEEN DISTANCE AND RADIAL VELOCITY AMONG EXTRA-GALACTIC NEBULAE. , 1929, Proceedings of the National Academy of Sciences of the United States of America.

[10]  G. Tilton,et al.  Isotopic lead investigations on the Allende carbonaceous chondrite , 1976 .

[11]  G. Mckay,et al.  Rare earth elements in Angra dos Reis and Lewis Cliff 86010, two meteorites with similar but distinct magma evolutions , 1990 .

[12]  S. Goldstein,et al.  The Pb isotopic compositions of lower crustal xenoliths and the evolution of lower crustal Pb , 1990 .

[13]  S. Galer,et al.  Age and isotopic relationships among the angrites Lewis Cliff 86010 and Angra dos Reis , 1992 .

[14]  G. Wasserburg,et al.  Sm-Nd isotopic evolution of chondrites and achondrites. II , 1984 .

[15]  G. Wetherill.  Discordant uranium‐lead ages: 2. Disordant ages resulting from diffusion of lead and uranium , 1963 .

[16]  G. Wasserburg,et al.  More anomalies from the Allende meteorite - Samarium , 1978 .

[17]  D. Unruh.  The UThPb age of equilibrated L chondrites and a solution to the excess radiogenic Pb problem in chondrites , 1982 .

[18]  C. Patterson,et al.  Age of meteorites and the earth , 1956 .

[19]  G. Desborough,et al.  U-Th-Pb and Rb-Sr systematics of Allende and U-Th-Pb systematics of Orgueil , 1976 .

[20]  G. Cressey,et al.  Thallium and lead in the Allende C3V carbonaceous chondrite. A study of the matrix phase , 1984 .

[21]  J. Wasson,et al.  Compositions of chondrites , 1988, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[22]  J. Silk,et al.  Dust Grains in a Hot Gas. Basic Physics , 1974 .

[23]  M. Tatsumoto,et al.  Time Differences in the Formation of Meteorites as Determined from the Ratio of Lead-207 to Lead-206 , 1973, Science.

[24]  K. Marti,et al.  Search for extinct146Sm, 1. The isotopic abundance of142Nd in the Juvinas meteorite , 1975 .

[25]  F. Podosek.  Dating of meteorites by the high-temperature release of iodine-correlated Xe129 , 1970 .

[26]  L. Grossman.  Petrography and mineral chemistry of Ca-rich inclusions in the Allende meteorite , 1975 .

[27]  E. Rutherford.  Origin of Actinium and Age of the Earth , 1929, Nature.

[28]  F. Podosek,et al.  Chondrite chronology by initial 87Sr/86Sr in phosphates? , 1991 .

[29]  G. Manhès,et al.  UPb systematics of phosphates from equilibrated ordinary chondrites , 1994 .

[30]  H. Barnes,et al.  Geochemistry of Hydrothermal Ore Deposits , 1968 .

[31]  G. Tilton,et al.  Sphene: Uranium-Lead Ages , 1968, Science.

[32]  John A. Wood,et al.  A chemical-petrologic classification for the chondritic meteorites. , 1967 .

[33]  J. Minster,et al.  87Rb87Sr dating of LL chondrites , 1981 .

[34]  G. Dreibus,et al.  Iodine abundances in oceanic basalts: implications for Earth dynamics , 1992 .

[35]  J. Minster,et al.  87Rb-87Sr Dating of L Chondrites: Effects of Shock and Brecciation , 1979 .

[36]  J. S. Dickey,et al.  Ca-Al rich phases in the allende meteorite , 1970 .

[37]  G. Wasserburg.  Isotopic abundances: inferences on solar system and planetary evolution , 1987 .

[38]  R. K. O’nions,et al.  The Lead, Neodymium and Strontium Isotopic Structure of Ocean Ridge Basalts , 1982 .

[39]  F. Hoyle,et al.  Nucleosynthesis during the Early History of the Solar System , 1962 .

[40]  L. L. Lundberg,et al.  Correlated study of initial Sr-87/Sr-86 and Al-Mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the Allende meteorite , 1991 .

[41]  G. Wasserburg,et al.  Sm-Nd isotopic evolution of chondrites , 1980 .

[42]  C. Patterson.  The Pb207/Pb206 ages of some stone meteorites , 1955 .

[43]  G. Wasserburg,et al.  Isotopic and chemical investigations on Angra dos Reis , 1977 .

[44]  J. H. Reynolds.  ISOTOPIC COMPOSITION OF PRIMORDIAL XENON , 1960 .

[45]  J. Minster,et al.  87Rb87Sr chronology of H chondrites: Constraint and speculations on the early evolution of their parent body , 1979 .

[46]  G. Tilton,et al.  Age of the Earth. , 1955, Science.

[47]  A. Holmes.  An Estimate of the Age of The Earth , 1946, Nature.

[48]  Ronghua Xu,et al.  The Pb-isotope geochemistry of granitoids from the Himalaya-Tibet collision zone: implications for crustal evolution , 1985 .

[49]  D. Clayton.  Cosmic Chemical Memory: A New Astronomy , 1985 .

[50]  A. H. Jaffey,et al.  Precision Measurement of Half-Lives and Specific Activities of U-235 and U238 , 1971 .

[51]  G. Wetherill.  Radiometric Chronology of the Early Solar System , 1975 .

[52]  J. Birck,et al.  Chronology and chemical history of the parent body of basaltic achondrites studied by the 87Rb-87Sr method , 1978 .

[53]  J. Birck,et al.  Manganese—chromium isotope systematics and the development of the early Solar System , 1988, Nature.

[54]  G. Wetherill,et al.  Rubidium-strontium age of hypersthene (L) chondrites , 1968 .

[55]  G. Wasserburg,et al.  The isotopic abundance of26Mg and limits on26Al in the early solar system , 1970 .

[56]  G. Tilton.  Isotopic lead ages of chondritic meteorites , 1973 .

[57]  E. Rutherford M.A. D.Sc.,et al.  LXIV. The cause and nature of radioactivity.—Part II , 1902 .

[58]  G. Wasserburg,et al.  The identification of early condensates from the solar nebula , 1973 .

[59]  P. K. Kuroda.  Nuclear Fission in the Early History of the Earth , 1960, Nature.

[60]  G. Wasserburg,et al.  Initial strontium isotopic abundances and the resolution of small time differences in the formation of planetary objects , 1968 .

[61]  H. Craig,et al.  The composition of the stone meteorites and the origin of the meteorites , 1953 .

[62]  G. Tilton,et al.  Early planetary metamorphism in chondritic meteorites , 1985 .

[63]  D. Wark,et al.  The nature and origin of type B1 and B2 CaAl-rich inclusions in the Allende meteorite , 1982 .

[64]  G. Manhès,et al.  Comparative uranium-thorium-lead and rubidium-strontium study of the Saint Sèverin amphoterite: consequences for early solar system chronology , 1978 .

[65]  S. Bergh.  Size and age of the universe. , 1981 .

[66]  N. Grevesse,et al.  Abundances of the elements: Meteoritic and solar , 1989 .

[67]  V. Murthy,et al.  Primary isochron of zero age for meteorites and the Earth , 1962 .

[68]  R. Clayton,et al.  A Component of Primitive Nuclear Composition in Carbonaceous Meteorites , 1973, Science.

[69]  E. Anders,et al.  Meteorites and the Early Solar System , 1971 .

[70]  M. Gaffey,et al.  Meteoritic parent bodies: nature, number, size and relation to present-day asteroids. , 1989 .

[71]  P. M. Jeffery,et al.  Origin of excess Xe129 in stone meteorites , 1961 .

[72]  L. Nyquist,et al.  THE ISOTOPIC RECORD OF LUNAR VOLCANISM , 1992 .

[73]  G. Wasserburg,et al.  Initial strontium for a chondrite and the determination of a metamorphism or formation interval , 1969 .

[74]  G. Wasserburg,et al.  The isotopic composition of uranium and lead in Allende inclusions and meteoritic phosphates , 1981 .

[75]  G. Wasserburg,et al.  Correction [to “Demonstration of 26Mg excess in Allende and evidence for 26Al”] , 1976 .

[76]  G. Wasserburg,et al.  Endemic isotopic anomalies in titanium , 1980 .

[77]  D. Clayton.  Extinct Radioactivities: Trapped Residuals of Presolar Grains , 1975 .

[78]  G. Wetherill.  Accumulation of the Terrestrial Planets , 1985 .

[79]  R. L. Stanton,et al.  Anomalous leads and the emplacement of lead sulfide ores , 1959 .

[80]  R. Hinton,et al.  Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites , 1984, Nature.

[81]  Albrecht W. Hofmann,et al.  The chemical composition of the Earth , 1995 .

[82]  A. Nier,et al.  The Isotopic Constitution of Lead and the Measurement of Geological Time. III , 1941 .

[83]  D. Clayton.  Interstellar fossil Mg-26 and its possible relationship to excess meteoritic Mg-26 , 1986 .

[84]  G. Manhès,et al.  U-Pb systematics in iron meteorites: Uniformity of primordial lead , 1985 .

[85]  A. Birch.  Biosynthesis of polyketides and related compounds. , 1967, Science.

[86]  J. Birck,et al.  Chromium isotopic anomalies in Allende Refractory Inclusions , 1984 .

[87]  W. White.  238U/204Pb in MORB and open system evolution of the depleted mantle , 1993 .

[88]  G. Wetherill,et al.  Rubidium‐strontium age of amphoterite (LL) chondrites , 1969 .

[89]  V. Safronov,et al.  Evolution of the protoplanetary cloud and formation of the earth and the planets , 1972 .

[90]  G. Wasserburg,et al.  U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks , 1972 .