The First Billion Years of the Geodynamo

地磁场的发生和性质对了解地核、大气和地球生命的演化具有重要意义。地磁场是在液态的外地核中产生的，因此是地核状况的探测。磁场还保护地球免受来自太阳的高能粒子流（“太阳风”）的伤害；如果没有这个保护层，地球可能会变成一个干燥贫瘠的星球。产生磁场的早期地核地球发电机的记录保存在火成岩中的古代硅酸盐晶体中，这些岩石含有微小的磁性颗粒包裹体。我们的数据表明，在34亿到34.5亿年前，接近固体内核开始增长的极限，地球发电机的存在。当时，磁场保护了地球大气层免受侵蚀，太阳风的作用大大减弱，这与现代极端太阳风暴期间的情况类似。这些情况表明，来自年轻太阳的强烈辐射可能通过促进轻元素和水的损失而改变了年轻地球的大气层。如果在34.5亿年前没有磁场，或者在内核生长之前有一个更古老的地球发电机产生了一个弱磁场，那么这种影响就会更加明显。总的来说，这些考虑表明年轻的地球比现在更富水。了解这些问题的新前沿是获得超过34.5亿年前的地磁场记录。我们正在通过研究6个古代大陆（克拉通）岩心的年代确定的岩石单元，研究地球动力学历史的前10亿年及其对地球演化的影响。我们结合了现有的原位火成岩单硅酸盐晶体磁性测量方法和沉积单元颗粒磁性分析的新方法。使用罗切斯特大学的高灵敏度磁力计可以实现这些测量。确定地球历史上第一个十亿年间地磁场的存在和强度对研究早期地球环境（大气和生物圈）和地核的一系列科学家具有广泛的兴趣。这项调查涉及到与几个国家的地质学家的国际合作，以及跨越天体物理学和空间物理学的多学科合作。我们的项目还整合了研究和教育工作。这项研究有助于研究生论文，本科生正在接受实地和实验室的培训。

The onset and nature of the geomagnetic field is important for understanding the evolution of the core, atmosphere and life on Earth. The geomagnetic field is generated in the liquid outer core, and hence is a probe of core conditions. The field also protects Earth from energetic particles streaming from the Sun (the "solar wind"); without this protective shield Earth might have developed into a dry and barren planet. A record of the early core geodynamo that generated the field is preserved in ancient silicate crystals from igneous rocks that contain minute magnetic grain inclusions. Our data indicate the presence of a geodynamo between 3.4 and 3.45 billion years ago, near the limit for the start of growth of the solid inner-core. While the magnetic field sheltered Earth's atmosphere from erosion at this time, the standoff of the solar wind was greatly reduced, and similar to that seen during modern extreme solar storms. These conditions suggest that intense radiation from the young Sun may have modified the atmosphere of the young Earth by promoting loss of light elements and water. Such effects would have been more pronounced if the field were absent prior to 3.45 billion years ago, as suggested in some hypotheses, or if an older geodynamo prior to inner core growth produced a weak field. In general, these considerations suggest the young Earth was more water-rich than today. The new frontier to learn more about these issues is obtaining geomagnetic field records that are more than 3.45 billion-years-old.We are investigating the first billion years of geodynamo history and its implications for Earth evolution through the study of well-dated rock units from 6 ancient cores of continents (cratons). We are using a combination of existing methods of single silicate crystal magnetic measurements from in situ igneous host rocks and new approaches involving magnetic analyses of grains from sedimentary units. These measurements are achievable using highly sensitive magnetometers at the University of Rochester. Determination of the presence and strength of the geomagnetic field during the first billion years of Earth history is of broad interest to a range of scientists who study early Earth environments (atmosphere and biosphere) and the core. The investigation involves international collaboration with geologists from several countries, and multidisciplinary collaborations spanning astrophysics and space physics. Our program also integrates research and educational efforts. The study is contributing to graduate theses and undergraduates are receiving training in the field and the laboratory.