Halliday Alex N
Department of Earth Sciences, ETH Zentrum, NO, Sonneggstrasse 5, Zürich, CH8092, Switzerland.
Nature. 2004 Feb 5;427(6974):505-9. doi: 10.1038/nature02275.
The degree to which efficient mixing of new material or losses of earlier accreted material to space characterize the growth of Earth-like planets is poorly constrained and probably changed with time. These processes can be studied by parallel modelling of data from different radiogenic isotope systems. The tungsten isotope composition of the silicate Earth yields a model timescale for accretion that is faster than current estimates based on terrestrial lead and xenon isotope data and strontium, tungsten and lead data for lunar samples. A probable explanation for this is that impacting core material did not always mix efficiently with the silicate portions of the Earth before being added to the Earth's core. Furthermore, tungsten and strontium isotope compositions of lunar samples provide evidence that the Moon-forming impacting protoplanet Theia was probably more like Mars, with a volatile-rich, oxidized mantle. Impact-driven erosion was probably a significant contributor to the variations in moderately volatile element abundance and oxidation found among the terrestrial planets.
新材料的有效混合或早期吸积物质向太空的损失在多大程度上表征类地行星的生长，目前约束不足，且可能随时间变化。这些过程可通过对来自不同放射性同位素系统的数据进行并行建模来研究。硅酸盐地球的钨同位素组成得出了一个吸积的模型时间尺度，该尺度比目前基于陆地铅和氙同位素数据以及月球样品的锶、钨和铅数据的估计要快。对此的一个可能解释是，撞击的核心物质在被添加到地球核心之前，并不总是能与地球的硅酸盐部分有效混合。此外，月球样品的钨和锶同位素组成提供了证据，表明形成月球的撞击原行星忒伊亚可能更像火星，具有富含挥发物的氧化地幔。撞击驱动的侵蚀可能是导致类地行星中中等挥发性元素丰度和氧化变化的一个重要因素。
