Discovering Hadean Earth

智力上的优点。地球历史的前5亿年--哈迪亚古代--是一段“失落”的时间，因为在这段时间里几乎没有保存下来的岩石记录。然而，Pi和他的同事们发现了来自西澳大利亚(杰克山)的碎屑状和捕虏晶状锆石样品，年龄在4.0到4.4Ga之间。一项大规模的分析活动已经确认了数以千计的这种古老的锆石，对这些颗粒的调查被解释为地球表面存在液态水，大陆地壳显著增长，成熟的沉积物再循环系统，可能是板块边界类型的过程在海甸期间的运作。这些证据表明，非常早期的行星可能比之前认为的更类似于今天的地球，这刺激了新的测量，并证明了新的测量是合理的。提出了分析发展、分析程序和实验，以解决以下问题：1)海德岛杰克山锆石是否可能是撞击形成的？2)海德岛锆石是否记录了~3.9Ga月球大灾难的陆上对应关系？3)3.9-4.3Ga锆石中的高丰度(低Lu/Hf)储集层发生了什么？4)4Ga锆石中的矿物包裹体是否保留了原始的海德岛记录？5)可用于研究海德岛锆石中的包裹体的气压计？6)海德岛锆石中的Pu-U变化是否反映了水介导的分馏作用？以及7)集体的同位素、矿物学和测温数据是Hadean大陆再循环和板块边界相互作用的证据吗？拟议的研究包括：1)激光烧蚀ICPMS测量3.9-3.6Ga锆石中的初始176Hf/177Hf，2)4个Ga锆石的U-Th-Pb离子探针深度剖面，3)陆地撞击熔体中形成的锆石的表征，4)裂变Xe同位素的Hadean Pu-U地球化学，5)Jack Hills锆石的Nd同位素体系，6)微米级白云母中Si/Al的纳米SIMS分析，7)Hadean白云母包裹体的K-Ca定年，以及8)过铝花岗岩碰撞的SiIn-In-Muscovite气压计的标定。这项研究将直接惠及该项目资助的加州大学洛杉矶分校研究生。一旦接受了离子微探针的培训，这些学生就会反过来为NSF支持的Keck同位素地球化学中心的访问者(包括许多研究生)提供支持(见下文)。已经确定了几个将用于产生本科生研究机会的小项目。研究成果具有国际意义，如果哈迪亚范式被推翻，可能与行星探索任务的结果类似。该项目展示了在全球感兴趣的领域中的科学和技术领导地位，帮助激发考虑从事科学和技术职业的年轻人的想象力，并为青年科学家提供培训机会。研究成果将通过高引文影响力的科学期刊向科学界传播，并通过持续的外联活动向公众传播(见http://sims.ess.ucla.edu/outreach/outreach.php).

Intellectual merit. The first 500 million years of Earth history - the Hadean Eon - is a period of 'lost' time as there is virtually no rock record preserved from this interval. However, the PI and colleagues have samples of detrital and xenocrystic zircons from western Australia (Jack Hills) with ages between 4.0 and 4.4 Ga. A massive analysis campaign has identified many thousands of these ancient zircons, and investigations of these grains have been interpreted to suggest the presence of liquid water at the Earth's surface, significant growth of continental crust, a mature sediment recycling system, and perhaps operation of plate boundary-type processes during the Hadean. Such evidence suggests the possibility that the very early planet was much more similar to the present day Earth than previously thought and this stimulates and justifies new measurements. Analytical developments, analysis programs, and experiments are proposed to address the following questions: 1) Could Hadean Jack Hills zircons have been formed by impacts? 2) Do Hadean zircons record the terrestrial counterpart to the ~3.9 Ga lunar cataclysm? 3) What happened to the highly enriched (low Lu/Hf) reservoir seen in 3.9- 4.3 Ga zircons? 4) Do mineral inclusions in 4 Ga zircons retain a pristine Hadean record? 5) Are available barometers applicable to inclusions in Hadean zircons? 6) Do Pu-U variations in Hadean zircons reflect water-mediated fractionation? and 7) Are the collective isotopic, mineralogical, and thermometry data evidence of Hadean continental recycling and plate boundary interactions? Proposed investigations include: 1) Laser ablation ICPMS measurement of initial 176Hf/177Hf in 3.9-3.6 Ga zircons, 2) U-Th-Pb ion microprobe depth profiling of 4 Ga zircons, and 3) characterization of zircons formed in terrestrial impact melts, 4) Hadean Pu-U geochemistry from fission Xe isotopes, 5) Nd isotopic systematics of Jack Hills zircon, 6) NanoSIMS analysis of Si/Al in micron-sized muscovite, 7) K-Ca dating of Hadean muscovite inclusions, and 8) calibration of the Si-in-muscovite barometer forperaluminous granitoids.Broader Impacts. This research will directly benefit the UCLA graduate students supported by this project. Once trained on the ion microprobe, these students in turn provide support to visitors (including numerous graduate students) to the NSF-supported Keck Center for Isotope Geochemistry (see below). Several small projects have been identified that will be used to engender undergraduate research opportunities.Research outcomes are of international interest and could be akin to the results of a planetary exploration mission if the Hadean paradigm is overturned. This project showcases scientific and technical leadership in a field of global interest, aids in capturing the imagination of young people considering a career in science and technology, and provides training opportunities for young scientists. Research results will be communicated to the scientific community via high citation impact scientific journals and to the public through sustained outreach activities (see http://sims.ess.ucla.edu/outreach/outreach.php).