CAREER:Exploring the early Earth with high-resolution paleomagnetism

在地球历史的最初20亿年（距今45到25亿年），地球上的条件与现代地球有很大的不同。地球历史上的关键事件，包括生命的兴起和大陆的形成，都发生在这段时间，但一些基本问题仍未得到解答。早期的地球是否呈现出我们今天所看到的熟悉的大陆漂移模式？第一批产氧生物是什么时候进化的？是否有一个类似于当今地球磁场的全球磁场，使大气层不受太阳风的影响？该项目将使用新一代磁场成像设备，该设备是最近从量子传感技术的进步中开发出来的，用于检查年龄在27亿至42亿年之间的岩石样本的磁性。这些实验有望对板块构造的起源、早期大气的演化以及产氧生命的兴起产生新的见解。与这些测量同时，该项目将与波士顿地区的中学教师一起开发一系列课程，包括通过分发给学校的太阳望远镜，由学生主导对太阳进行观测。这些观测将作为太阳属性随时间变化及其对早期地球表面条件影响的介绍。了解太古宙（40 - 25亿年前，或Ga）时期地球状况的根本挑战是缺乏可以追溯到那个时期的保存完好的岩石。因此，由于铁磁相的变质作用和化学蚀变，普遍存在的再磁化严重阻碍了恢复古代磁场信息的努力。该项目将应用最近开发的微米级磁成像技术，即量子钻石显微镜（QDM），来解决太古宙地球历史上的主要悬而未决的问题。QDM的高空间分辨率使其能够直接成像复杂蚀变岩石中的剩余磁化载体，从而有助于识别原始古磁信号。在任务1中，QDM将通过恢复来自南非巴伯顿绿岩带（BGB）新发现的3.3-4.2 Ga锆石群的磁信号来推断3.5 Ga之前地球发电机的存在。作为任务2的一部分，项目团队将在精心挑选的火成岩单元上应用QDM和传统的古地磁技术，以量化3.45 Ga岩石圈板块的流动性。最后，该项目的任务3将使用QDM来推断保存在2.78 Ga微陨石中的铁磁性氧化铁的来源，从而验证大氧化事件发生前几亿年前地球上层大气富含氧气的有争议的假设。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Conditions on the Earth during the first two billion years of its history (4.5 to 2.5 billion years before present) were vastly different from the modern Earth. Key events in Earth history, including the rise of life and the creation of continents, took place during this time, yet fundamental questions remain unanswered. Did the early Earth exhibit the familiar patterns of continental drift as we see today? When did the first oxygen-producing organisms evolve? Did a global magnetic field similar to that of the present-day isolate the atmosphere from loss to the solar wind? This project will use a new generation magnetic field imaging device, recently developed from advances in quantum sensing, to examine the magnetic properties of rock samples between 2.7 and 4.2 billion years in age. These experiments are expected to yield new insights into the initiation of plate tectonics, the evolution of the early atmosphere, and the rise of oxygen-producing life. In parallel with these measurements this project will develop a series of lessons with Boston-area middle school teachers involving student-led observations of the sun through solar telescopes distributed to the schools. These observations will serve as an introduction to changes in the sun's properties through time and its impact on surface conditions on the early Earth.The fundamental challenge to understanding conditions on Earth during the Archean Eon (4.0-2.5 billion years ago, or Ga) is the lack of well-preserved rocks dating from that time. Consequently, attempts to recover information about ancient magnetic fields have been severely hampered by pervasive remagnetization through metamorphism and chemical alteration of ferromagnetic phases. This project will apply a recently developed technology for micrometer-scale magnetic imaging, known as the quantum diamond microscope (QDM), to address major outstanding questions in Archean Earth history. The high spatial resolution of the QDM permits direct imaging of remanent magnetization carriers in complex, altered rocks, which aids the identification of primary paleomagnetic signals. In Task 1, the QDM will be used to infer the existence of the geodynamo before 3.5 Ga by recovering magnetic signals from a newly discovered population of 3.3-4.2 Ga zircons from the Barberton Greenstone Belt (BGB) of South Africa. As part of Task 2, the project team will apply both QDM and traditional paleomagnetic techniques on carefully selected igneous rock units to quantify the mobility of lithospheric plate at 3.45 Ga. Finally, Task 3 of the project will use the QDM to infer the origin of ferromagnetic iron oxides preserved in 2.78 Ga micrometeorites, thereby testing the controversial hypothesis that the upper atmosphere of the Earth was oxygen-rich several hundred million years before the Great Oxidation Event.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.