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1.
Nature ; 436(7051): 655-9, 2005 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-16079836

RESUMO

The nitrogen in lunar soils is correlated to the surface and therefore clearly implanted from outside. The straightforward interpretation is that the nitrogen is implanted by the solar wind, but this explanation has difficulties accounting for both the abundance of nitrogen and a variation of the order of 30 per cent in the 15N/14N ratio. Here we propose that most of the nitrogen and some of the other volatile elements in lunar soils may actually have come from the Earth's atmosphere rather than the solar wind. We infer that this hypothesis is quantitatively reasonable if the escape of atmospheric gases, and implantation into lunar soil grains, occurred at a time when the Earth had essentially no geomagnetic field. Thus, evidence preserved in lunar soils might be useful in constraining when the geomagnetic field first appeared. This hypothesis could be tested by examination of lunar farside soils, which should lack the terrestrial component.


Assuntos
Planeta Terra , Meio Ambiente Extraterreno/química , Sedimentos Geológicos/química , Modelos Teóricos , Lua , Nitrogênio/análise , Gases Nobres/análise , Atmosfera/química , História Antiga , Íons/análise , Magnetismo , Isótopos de Nitrogênio , Vento
2.
Science ; 175(4020): 423-5, 1972 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-17731363

RESUMO

The last lava flow in the Hadley Rille area of Mare Imbrium, as inferred from an argon-40-argon-39 experiment on a plagioclase separate from the lunar basalt 15555, occurred 3.31+/-0.03x10(9) years ago. An argon-40-argon-39 experiment on a whole rock sample shows significant loss of radiogenic argon-40 and yields a well-defined, high-temperature plateau indicating a lower age of 3.22+/-0.03x10(9) years. A cosmic-ray exposure age of 90+/-10x10(6) years is determined from the ratio of spallogenic argon-38 to calcium.

3.
Science ; 156(3772): 233-6, 1967 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-17741144

RESUMO

Measurements of the accumulation of Xe(l29) from radioactive decay of extinct 1(129) in meteorites show that the 1(129)/ 1(127) ratio in high-temperature minerals in diverse chondrites was 10(-4) at the time of cooling. The uniformity in the ratio indicates that the minerals cooled simultaneously within 1 or 2 million years.

4.
Science ; 167(3918): 463-6, 1970 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-17781453

RESUMO

The (87)Rb-(87)Sr internal isochrons for five rocks yield an age of 3.65 +/-0.05 x 10(9) years which presumably dates the formation of the Sea of Tranquillity. Potassium-argon ages are consistent with this result. The soil has a model age of 4.5 x10(9) years, which is best regarded as the time of initial differentiation of the lunar crust. A peculiar rock fragment from the soil gave a model age of 4.44 x 10(9) years. Relative abundances of alkalis do not suggest differential volatilization. The irradiation history of lunar rocks is inferred from isotopic measurements of gadolinium, vanadium, and cosmogenic rare gases. Spallation xenon spectra exhibit a high and variable (131)Xe/(126)Xe ratio. No evidence for (129)I was found. The isotopic composition of solar-wind xenon is distinct from that of the atmosphere and of the average for carbonaceous chondrites, but the krypton composition appears similar to average carbonaceous chondrite krypton.

5.
Science ; 175(4023): 795, 1972 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-17836140
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