CAREER: Habitability of the Hadean Earth - A South African perspective

地球是已知的唯一拥有生命的行星，但地球何时变得适合居住仍存在争议。最初，地球不适合居住，因为它被岩浆海洋覆盖，经常受到巨大的撞击。随着时间的推移，第一个地壳结晶，海洋沉淀，大陆开始形成。然而，我们不知道这些过程是什么时候发生的，也不知道地球何时变得宜居。这是因为缺少地球最初的5.5亿年历史--Hadean Eon的摇滚记录。当时仅存的材料是锆石。我们的大部分知识来自于赫迪亚锆石的单一位置，即澳大利亚的杰克山。最近，Pi的团队在南非发现了Hadean锆石。这为进入Hadean Eon提供了第二个镜头。这些锆石中的微量元素和同位素将有助于解决对地球宜居性至关重要的过程。这包括板块构造的开始，地幔的放出气体，以及海平面以上地壳的出现。拟议的研究提供了将研究和教育经验结合在一起的共生机会。少年派将创建一个博物馆展览，在哈佛自然历史博物馆和埃斯瓦蒂尼的Ngwenya博物馆展出。这项研究也为来自少数族裔的本科生提供了大量的研究机会。最后，将分发改进的本科生和研究生教材，以便更广泛地使用。该项目支持一名女性早期职业科学家、一名博士后研究员和10名本科生研究助理。拟议的工作将通过分析大量统计上可靠的锆石，并通过拓宽和整合锆石同位素(Hf、O、Si)以及痕量和稀土元素地球化学分析，创建杰克山以外的第一个Hadean锆石大型数据集。这项研究考察了南非绿砂岩床中的Hadean锆石，这些锆石之前是通过单独的拨款收集、提取和测定年代的。首先，通过对锆石Hf、O同位素、微量元素的综合研究和模拟，验证锆石是形成于停滞盖层环境还是活动盖层环境(即板块构造)。其次，它将评估地幔成因的锆石中氧化还原敏感的Ce异常，以评估地幔的氧化状态。与来自Singhbhum Craton和Jack Hills的Hadean锆石数据的比较将提供对地幔不均一性的限制。第三，它将评估同位素(O，Si)和地球化学替代物(Al，P)，以测试粘土的生成和大气水的存在，作为大陆出现的替代物。研究成果将通过在期刊上发表文章、在会议上发表演讲和提交到在线数据库来传播。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Earth is the only planet known to harbor life, but when Earth became habitable is still debated. Initially, Earth was uninhabitable because it was covered by a magma ocean and frequently struck by giant impactors. Through time, the first crust crystallized, oceans precipitated, and continents started forming. Yet, we don't know when these processes occurred and when Earth became habitable. This is due to lack of a rock record for Earth’s first ~550 million years of history, the Hadean Eon. The only remaining materials from that time are zircons. Most of our knowledge comes from a single location of Hadean zircons, the Jack Hills in Australia. Recently, the PI’s team discovered Hadean zircon in South Africa. This offers a second lens into the Hadean Eon. Trace elements and isotopes of these zircons will help address processes key to Earth’s habitability. This includes the onset of plate tectonics, outgassing from the mantle, and the emergence of crust above sea level. The proposed research offers symbiotic opportunities to integrate research and educational experiences. The PI will create a museum exhibit to be shown at the Harvard Museum of Natural History and the Ngwenya museum in Eswatini. The research also offers abundant research opportunities for undergraduates from underrepresented minorities. Lastly, improved undergraduate and graduate teaching materials will be disseminated for broader use. The project supports one female early career scientist, one postdoctoral researcher, and 10 undergraduate research assistants.The proposed work will create the first large dataset of Hadean zircon outside the Jack Hills by analyzing a statistically robust number of zircons and by broadening and integrating zircon isotopic (Hf, O, Si) and trace and rare earth element geochemical analyses. The research examines Hadean zircons from the Green Sandstone Bed, South Africa, that were previously collected, extracted, and dated through a separate grant. Firstly, the research will test whether the zircons formed in a stagnant-lid or mobile-lid (i.e., plate tectonics) environment through an integrated study of zircon Hf and O isotopes, trace elements and with modeling. Secondly, it will assess redox-sensitive Ce anomalies in mantle-derived zircons to evaluate the oxidation state of the mantle. A comparison to data from Hadean zircons of the Singhbhum Craton and the Jack Hills will provide constraints on mantle heterogeneity. Thirdly, it will assess isotopic (O, Si) and geochemical proxies (Al, P) to test for the generation of clays and the presence of meteoric waters as proxies for continental emergence through time. The research results will be disseminated through articles in journals, presentations at conferences, and submission to online databases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.