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147Sm-143Nd systematics of Earth are inconsistent with a superchondritic Sm/Nd ratio.

ABSTRACT: The relationship between the compositions of the Earth and chondritic meteorites is at the center of many important debates. A basic assumption in most models for the Earth's composition is that the refractory elements are present in chondritic proportions relative to each other. This assumption is now challenged by recent (142)Nd/(144)Nd ratio studies suggesting that the bulk silicate Earth (BSE) might have an Sm/Nd ratio 6% higher than chondrites (i.e., the BSE is superchondritic). This has led to the proposal that the present-day (143)Nd/(144)Nd ratio of BSE is similar to that of some deep mantle plumes rather than chondrites. Our reexamination of the long-lived (147)Sm-(143)Nd isotope systematics of the depleted mantle and the continental crust shows that the BSE, reconstructed using the depleted mantle and continental crust, has (143)Nd/(144)Nd and Sm/Nd ratios close to chondritic values. The small difference in the ratio of (142)Nd/(144)Nd between ordinary chondrites and the Earth must be due to a process different from mantle-crust differentiation, such as incomplete mixing of distinct nucleosynthetic components in the solar nebula.

SUBMITTER: Huang S

PROVIDER: S-EPMC3612654 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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147Sm-143Nd systematics of Earth are inconsistent with a superchondritic Sm/Nd ratio.

Huang Shichun S Jacobsen Stein B SB Mukhopadhyay Sujoy S

Proceedings of the National Academy of Sciences of the United States of America 20130311 13

The relationship between the compositions of the Earth and chondritic meteorites is at the center of many important debates. A basic assumption in most models for the Earth's composition is that the refractory elements are present in chondritic proportions relative to each other. This assumption is now challenged by recent (142)Nd/(144)Nd ratio studies suggesting that the bulk silicate Earth (BSE) might have an Sm/Nd ratio 6% higher than chondrites (i.e., the BSE is superchondritic). This has le ...[more]

PMID: 23479630

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Project description:Biomedical implants and devices for tissue engineering in clinics, mainly made of polymers and stiff metallic materials, require possibly secondary surgery or life-long medicine. Biodegradable metals for biomedical implants and devices exhibit huge potential to improve the prognosis of patients. In this work, we developed a new type of biodegradable binary zinc (Zn) alloys with 16 rare earth elements (REEs) including Sc, Y, La to Nd, and Sm to Lu, respectively. The effects of REEs on the alloy microstructure, mechanical properties, corrosion behavior and in vitro and in vivo biocompatibility of Zn were systematically investigated using pure Zn as control. All Zn-RE alloys generally exhibited improved mechanical properties, and biocompatibilities compared to pure Zn, especially the tensile strength and ductility of Zn-RE alloys were dramatically enhanced. Among the Zn-RE alloys, different REEs presented enhancement effects at varied extent. Y, Ho and Lu were the three elements displaying greatest improvements in majority of alloys properties, while Eu, Gd and Dy exhibited least improvement. Furthermore, the Zn-RE alloys were comparable with other Zn alloys and also exhibited superior properties to Mg-RE alloys. The in vivo experiment using Zn–La, Zn–Ce, and Zn–Nd alloys as tibia bone implants in rabbit demonstrated the excellent tissue biocompatibility and much more obvious osseointegration than the pure Zn control group. This work presented the significant potential of the developed Zn-RE binary alloys as novel degradable metal for biomedical implants and devices. Graphical abstract (a) Material preparation and characterizations. (b) Mechanical Properties and (c) Bone-implant interfaces.Image 1 Highlights • Novel binary Zn alloys with 16 rare earth elements including Sc, Y, La–Nd, Sm–Lu were firstly developed.• The alloying of rare earth element increased the tensile strength and elongation rate of pure Zn.• The Y, Ho, and Lu were the three elements that signficantly improved most of properties of Zn.• The binary Zn-RE alloys display superior property enhancement from rare earth element compared to Mg-RE alloys.• The in vivo implantation of the Zn–La, Zn–Ce, and Zn–Nd alloys exhibited much more obvious osseointegration than the pure Zn.

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147Sm-143Nd systematics of Earth are inconsistent with a superchondritic Sm/Nd ratio.

Publications

147Sm-143Nd systematics of Earth are inconsistent with a superchondritic Sm/Nd ratio.

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