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The isotope 146Sm undergoes α-decay to 142Nd, with a half-life of 103 million years. Measurable variations in the 142Nd/144Nd values of rocks resulting from Sm–Nd fractionation could therefore only have been produced within about 400 million years of the Solar System’s formation (that is, when 146Sm was extant). The 142Nd/144Nd compositions of terrestrial rocks are accordingly a sensitive monitor of the main silicate differentiation events that took place in the early Earth. High 142Nd/144Nd values measured in some Archaean rocks from Greenland hint at the existence of an early incompatible-element-depleted mantle. Here we present measurements of low 142Nd/144Nd values in 1.48-gigayear-(Gyr)-old lithospheric mantle-derived alkaline rocks from the Khariar nepheline syenite complex in southeastern India. These data suggest that a reservoir that was relatively enriched in incompatible elements formed at least 4.2 Gyr ago and traces of its isotopic signature persisted within the lithospheric root of the Bastar craton until at least 1.48 Gyr ago. These low 142Nd/144Nd compositions may represent a diluted signature of a Hadean (4 to 4.57 Gyr ago) enriched reservoir that is characterized by even lower values. That no evidence of the early depleted mantle has been observed in rocks younger than 3.6 Gyr (refs 3, 4, 7) implies that such domains had effectively mixed back into the convecting mantle by then. In contrast, some early enriched components apparently escaped this fate. Thus, the mantle sampled by magmatism since 3.6 Gyr ago may be biased towards a depleted composition that would be balanced by relatively more enriched reservoirs that are ‘hidden’ in Hadean crust, the D′′ layer of the lowermost mantle or, as we propose here, also within the roots of old cratons. [ABSTRACT FROM AUTHOR]

The recent discovery of diamond–graphite inclusions in the Earth’s oldest zircon grains (formed up to 4,252 Myr ago) from the Jack Hills metasediments in Western Australia provides a unique opportunity to investigate Earth’s earliest known carbon reservoir. Here we report ion microprobe analyses of the carbon isotope composition of these diamond–graphite inclusions. The observed δ13CPDB values (expressed using the PeeDee Belemnite standard) range between -5 per mil and -58 per mil with a median of -31 per mil. This extends beyond typical mantle values of around -6 per mil to values observed in metamorphic and some eclogitic diamonds that are interpreted to reflect deep subduction of low-δ13CPDB biogenic surface carbon. Low δ13CPDB values may also be produced by inorganic chemical reactions, and therefore are not unambiguous evidence for life on Earth as early as 4,250 Myr ago. Regardless, our results suggest that a low-δ13CPDB reservoir may have existed on the early Earth. [ABSTRACT FROM AUTHOR]

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same δ37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition. [ABSTRACT FROM AUTHOR]

The article reviews a report from Andersen et al published in the issue on how using isotope ratios of the element uranium through multiple-collector inductively coupled plasma mass spectrometers (MCICPMS) provides temporal constraints on crystal-recycling processes. It focuses on the hypothesis that oceanic crust, when returned to the Earth's mantle during collisions between tectonic plates, could influence the chemistry of Earth's interior and can be seen in ocean island basalts (OIBS).

This article discusses a study which examined sulphur isotopes in rocks from the ridge beneath the Atlantic Ocean. Conducted by J. Labidi et al., the study used an analytic technique to recover sulphur from rock samples and analyzed fingerprints of the isotopes. Results suggested that a substantial fraction of sulphur at the surface of the Earth is left over from the formation of its core.

The article reports on the findings of the study concerning the tungsten-isotope measurement of lunar rocks and formation of the moon. It reveals that the moon comprises 30 percent of the Earth's mass and it's crust was formed 70-150 million years after the accretion of solar system. It is believed that the moon was formed 62-90 million years after the solar system and 16 million years after the Earth's core and lunar crust. Furthermore, the findings support the slower rate of magma-ocean solidification obtained from the samarium and neodymium data.