Age of the Moon: An Isotopic Study of Uranium-Thorium-Lead Systematics of Lunar Samples
Tóm tắt
Concentrations of U, Th, and Pb in Apollo 11 samples studied are low (U. 0.16 to 0.87; Th, 0.53 to 3.4; Pb, 0.29 to 1.7, in ppm) but the extremely radiogenic lead in samples allows radiometric dating. The fine dust and the breccia have a concordant age of 4.66 billion years on the basis of 207 Pb/ 206 Pb, 206 Pb/ 238 U, 207 Pb/ 235 U, and 208 Pb/ 232 Th ratios. This age is comparable with the age of meteorites and with the age generally accepted for the earth. Six crystalline and vesicular samples are distinctly younger than the dust and breccia. The 238 U/ 235 U ratio is the same as that in earth rocks, and 234 U is in radioactive equilibrium with parent 238 U.
Từ khóa
Tài liệu tham khảo
BATE, G, THORIUM IN STONE METEORITES BY NEUTRON ACTIVATION ANALYSIS, GEOCHIMICA ET COSMOCHIMICA ACTA 16: 88 (1959).
BURNETT, D.S., EVIDENCE FOR FORMATION OF AN IRON METEORITE AT 3.8 BY 109 YEARS, EARTH AND PLANETARY SCIENCE LETTERS 2: 137 (1967).
BURNETT, D.S., 7RB-87SR AGES OF SILICATE INCLUSIONS IN IRON METEORITES, EARTH AND PLANETARY SCIENCE LETTERS 2: 397 (1967).
CAMERON, A.E., MASS SPECTROMETRY OF NANOGRAM-SIZE SAMPLES OF LEAD, ANALYTICAL CHEMISTRY 41: 525 (1969).
CHOW, T.J., THE OCCURRENCE AND SIGNIFICANCE OF LEAD ISOTOPES IN PELAGIC SEDIMENTS, GEOCHIMICA ET COSMOCHIMICA ACTA 26: 263 (1962).
KNIGHT, R. J., GEOLOGICAL SOCIETY OF AMERICA SPECIAL PAPERS 101 218 (1968).
Oversby V. M. Journal of Geophysical Research in press.
PATTERSON, C, THE SIGNIFICANCE OF LEAD ISOTOPES IN DETRITAL FELDSPAR WITH RESPECT TO CHEMICAL DIFFERENTIATION WITHIN THE EARTHS MANTLE, GEOCHIMICA ET COSMOCHIMICA ACTA 28: 1 (1964).
REED, G.W., DETERMINATIONS OF CONCENTRATIONS OF HEAVY ELEMENTS IN METEORITES BY ACTIVATION ANALYSIS, GEOCHIMICA ET COSMOCHIMICA ACTA 20: 122 (1960).
ROSHOLT, J. N., U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 575-B 133 (1967).
RUSSELL, R.D., DATING GALENAS BY MEANS OF THEIR ISOTOPIC CONSTITUTIONS .2., GEOCHIMICA ET COSMOCHIMICA ACTA 19: 41 (1960).