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"d, James M"
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Zinc isotopic evidence for the origin of the Moon
Lunar magmatic rocks are shown to be enriched in the heavy isotopes of zinc and to have lower zinc concentrations than terrestrial or Martian igneous rocks; these variations represent the large-scale evaporation of zinc, most probably in the aftermath of the Moon-forming giant impact event.
Zinc supports giant-impact theory of Moon formation
The heavily favoured theory for the origin of the Earth–Moon system is a giant impact between the proto-Earth and a Mars-sized body. Such a cataclysmic event would have left its mark on the isotopic composition of the Moon, because light isotopes evaporate more readily than heavier ones. Zinc in particular is a powerful indicator of the volatile histories of planets — it undergoes strong isotopic fractionation in planetary rocks, but is hardly fractionated following volcanic activity on Earth. This study compares high-precision zinc isotopic data for lunar basalts, Martian meteorites and terrestrial igneous rocks, and finds that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or Martian samples. The authors conclude that these variations are the result of large-scale evaporation of zinc in the aftermath of the Moon-forming giant-impact event.
Volatile elements have a fundamental role in the evolution of planets. But how budgets of volatiles were set in planets, and the nature and extent of volatile-depletion of planetary bodies during the earliest stages of Solar System formation remain poorly understood
1
,
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. The Moon is considered to be volatile-depleted and so it has been predicted that volatile loss should have fractionated stable isotopes of moderately volatile elements
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. One such element, zinc, exhibits strong isotopic fractionation during volatilization in planetary rocks
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,
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, but is hardly fractionated during terrestrial igneous processes
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, making it a powerful tracer of the volatile histories of planets. Here we present high-precision zinc isotopic and abundance data which show that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or Martian igneous rocks. Conversely, Earth and Mars have broadly chondritic zinc isotopic compositions. We show that these variations represent large-scale evaporation of zinc, most probably in the aftermath of the Moon-forming event, rather than small-scale evaporation processes during volcanism. Our results therefore represent evidence for volatile depletion of the Moon through evaporation, and are consistent with a giant impact origin for the Earth and Moon.
Journal Article
Peter Pan
The adventures of the three Darling children in Never-Never Land with Peter Pan, the boy who would not grow up.
Book
Tungsten-182 heterogeneity in modern ocean island basalts
New tungsten isotope data for modern ocean island basalts (OIB) from Hawaii, Samoa, and Iceland reveal variable 182W/184W, ranging from that of the ambient upper mantle to ratios as much as 18 parts per million lower. The tungsten isotopic data negatively correlate with ³He/⁴He. These data indicate that each OIB system accesses domains within Earth that formed within the first 60 million years of solar system history. Combined isotopic and chemical characteristics projected for these ancient domains indicate that they contain metal and are repositories of noble gases. We suggest that the most likely source candidates are mega–ultralow-velocity zones, which lie beneath Hawaii, Samoa, and Iceland but not beneath hot spots whose OIB yield normal 182W and homogeneously low ³He/⁴He.
Journal Article
Stochastic Late Accretion to Earth, the Moon, and Mars
Core formation should have stripped the terrestrial, lunar, and martian mantles of highly siderophile elements (HSEs). Instead, each world has disparate, yet elevated HSE abundances. Late accretion may offer a solution, provided that ≥0.5% Earth masses of broadly chondritic planetesimals reach Earth's mantle and that approximately 10 and approximately 1200 times less mass goes to Mars and the Moon, respectively. We show that leftover planetesimal populations dominated by massive projectiles can explain these additions, with our inferred size distribution matching those derived from the inner asteroid belt, ancient martian impact basins, and planetary accretion models. The largest late terrestrial impactors, at 2500 to 3000 kilometers in diameter, potentially modified Earth's obliquity by approximately 10°, whereas those for the Moon, at approximately 250 to 300 kilometers, may have delivered water to its mantle.
Journal Article
Superman : President Luthor
His fame bolstered after helping to rebuild Gotham City after an earthquake, billionaire Lex Luthor decides to run for the highest office in the land, the American presidency.
Book
A changing thermal regime revealed from shallow to deep basalt source melting in the Moon
Sample return missions have provided the basis for understanding the thermochemical evolution of the Moon. Mare basalt sources are likely to have originated from partial melting of lunar magma ocean cumulates after solidification from an initially molten state. Some of the Apollo mare basalts show evidence for the presence in their source of a late-stage radiogenic heat-producing incompatible element-rich layer, known for its enrichment in potassium, rare-earth elements, and phosphorus (KREEP). Here we show the most depleted lunar meteorite, Asuka-881757, and associated mare basalts, represent ancient (~3.9 Ga) partial melts of KREEP-free Fe-rich mantle. Petrological modeling demonstrates that these basalts were generated at lower temperatures and shallower depths than typical Apollo mare basalts. Calculated mantle potential temperatures of these rocks suggest a relatively cooler mantle source and lower surface heat flow than those associated with later-erupted mare basalts, suggesting a fundamental shift in melting regime in the Moon from ~3.9 to ~3.3 Ga.
Ancient (~3.9 Ga) KREEP-free basalts were sourced from a relatively cool and shallow pyroxene-rich mantle distinct from later-erupted (<3.8 Ga) KREEP-bearing basalts, indicating a fundamental change in melting regimes in the Moon.
Journal Article