The First Billion Years of the Geodynamo

地球发电机的第一个十亿年

• 批准号: 1015269
• 负责人: John Tarduno
• 金额: $ 48.66万
• 依托单位: University of Rochester
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1015269&HistoricalAwards=false
• 关键词: First; Billion; Years; Geodynamo

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.

地磁场的开始和性质对于了解地核、大气和地球生命的演变非常重要。地磁场产生于液态的外核，因此它是探测地核状况的探针。磁场还保护地球免受来自太阳的高能粒子流（“太阳风”）的影响;如果没有这个保护罩，地球可能会发展成为一个干燥和贫瘠的星球。早期地核地球发电机的记录，产生的领域是保存在古老的硅酸盐晶体从火成岩含有微小的磁性颗粒夹杂物。我们的数据表明，在34亿至34.5亿年前，地球发电机的存在，接近固体内核开始增长的极限。虽然磁场保护了地球大气层免受侵蚀，但太阳风的对峙程度大大降低，与现代极端太阳风暴期间的情况相似。这些条件表明，来自年轻太阳的强烈辐射可能通过促进轻元素和水的流失而改变了年轻地球的大气层。如果磁场在34.5亿年前就不存在，这种效应会更加明显，就像一些假设所建议的那样，或者如果一个更古老的地球发电机在内核生长之前产生了一个弱场。总的来说，这些因素表明年轻的地球比今天更富含水。了解这些问题的新前沿是获得超过34.5亿年的地磁场记录。我们正在研究地球发电机历史的第一个10亿年及其对地球演化的影响，通过研究来自6个古老大陆核（古陆）的年代久远的岩石单元。我们正在使用现有的方法相结合的单硅酸盐晶体磁性测量从原位火成岩寄主岩石和新的方法，涉及磁性分析的颗粒从沉积单元。使用罗切斯特大学的高灵敏度磁力计可以实现这些测量。 确定地球历史头10亿年期间地磁场的存在和强度，是研究早期地球环境（大气和生物圈）和地核的一系列科学家的广泛兴趣。调查涉及与来自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。我们的计划还整合了研究和教育工作。这项研究有助于撰写研究生论文，本科生正在实地和实验室接受培训。