CSEDI Collaborative Research: The nature and timing of Earth's accretion

地球是由较小的岩石天体之间的一系列碰撞形成的。在这个过程中的某个时候，地球还获得了组成其大气和海洋的元素，称为挥发物。但地球是如何和何时形成的，以及它是如何和何时获得挥发物的，仍然非常不确定。这一点很重要，因为挥发性元素对我们所知的生命是必不可少的；如果我们能够理解地球是如何获得其挥发物的，这将有助于我们理解太阳系和其他地方的其他行星是如何做到这一点的。为了解决这个问题，调查人员使用了两个主要工具。一种是一系列天然的“时钟”，源自衰变的放射性元素；这些告诉我们事情发生得有多快。第二个是实验，以确定挥发性元素是否被隔离在地球的铁核中，或者它们是否留在了岩石和大气中。作为这项调查的一部分，该团队将对研究生和本科生--其中一些来自代表性不足的少数族裔--进行实验和分析技术培训，增加受过技术培训的劳动力。在这项建议中，调查人员探索挥发损失和核心封存对一系列中等挥发性和难熔元素的综合影响。他们将使用四个具有不同半衰期和化学特性的同位素计时器(Hf-W、Pd-Ag、U-Pb和I-Pu-Xe)来解开这两个影响。建模工作使用N体吸积模型，从而能够追踪物源和同位素演化；他们还建议对分配行为和地幔Xe同位素组成进行必要的实验测量。该团队将使用四个同位素系统来回答三个主要问题：1)大钉子或传统的吸积情景与观测结果更一致？2)随着吸积过程的进行，加入到地球中的物质的组成是如何变化的？3)吸积过程中和之后发生了多少挥发性损失？在回答这些问题时，研究人员将提供更有针对性的地球形成和最早演化的图景。这项拟议的研究涉及模型师、同位素地球化学家和高压矿物学家之间的跨学科合作。因此，它跨越了传统的学科界限，将为三个小组提供相互教育并整合实验、测量和建模的机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Earth formed by a series of collisions between smaller rocky bodies. At some point during this process, the Earth also acquired the elements, known as volatiles, that make up its atmosphere and oceans. But how and when the Earth formed, and how and when it acquired its volatiles, are still very uncertain. This matters, because the volatile elements are essential for life as we know it; if we can understand how the Earth acquired its volatiles, that will help us understand how other planets did so, in this solar system and elsewhere. To solve this problem the investigators use two main tools. One is a series of natural “clocks”, derived from radioactive elements that decay; these tell us how fast things happened. The second is experiments to determine whether the volatile elements were sequestered into the Earth’s iron core, or whether they were left behind in the rocks and atmosphere. As part of this investigation the team will train graduate and undergraduate students – some from under-represented minorities - in experimental and analytical techniques, adding to the technically-trained workforce.In this proposal the investigators explore the combined effects of volatile loss and core sequestration on a range of moderately volatile and refractory elements. They will use four isotopic chronometers (Hf-W, Pd-Ag, U-Pb and I-Pu-Xe), with different half-lives and chemical characteristics, to disentangle these two effects. The modeling efforts use N-body accretion models, allowing provenance to be tracked and isotopic evolution to be tracked; they also propose to carry out necessary experimental measurements on partitioning behavior and mantle Xe isotopic compositions. The team will use the four isotopic systems to answer three major questions: 1) are the Grand Tack or conventional accretion scenarios more consistent with the observations? 2) how did the composition of material added to the Earth change as accretion proceeded?; 3) how much volatile loss happened during and after accretion itself? In answering these questions the investigators will provide a more focused picture of the formation and earliest evolution of the Earth. The proposed research involves an inter-disciplinary collaboration between a modeler, an isotope geochemist and a high-pressure mineralogist. As such, it cuts across traditional disciplinary boundaries and will provide an opportunity for the three groups to educate each other and integrate experiments, measurements and modeling.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.