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理解地球核心、大气和生命的演化非常重要。地磁场是在液态外核中产生的，因此是一个探测核心条件的探测器。该磁场还保护地球免受来自太阳的高能粒子(“太阳风”)的伤害；如果没有这种保护屏障，地球可能会发展成一个干燥而贫瘠的星球。产生磁场的早期核心地球发电机的记录保存在来自火成岩的古老硅酸盐晶体中，这些晶体含有微小的磁性颗粒包裹体。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。虽然此时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。如果像一些假说所说的那样，在34.5亿年前没有磁场，或者如果在内核生长之前较老的地球发电机产生了弱场，这样的影响会更加明显。总体而言，这些考虑表明，年轻的地球比今天更富水。更多了解这些问题的新前沿是获取超过34.5亿年的地磁场记录。我们正在通过研究大陆(克拉通)6个古老核心(克拉通)的定年岩石单位来调查地球发电机历史的第一个10亿年及其对地球演化的影响。我们正在使用现有的从原地火成岩中进行单硅酸盐晶体磁性测量的方法和对沉积单元中的颗粒进行磁性分析的新方法。这些测量可以使用罗切斯特大学的高灵敏度磁力计来实现。研究早期地球环境(大气层和生物圈)和地球核心的一系列科学家对确定地球历史最初10亿年期间地磁场的存在和强度具有广泛的兴趣。这项调查涉及与几个国家的地质学家的国际合作，以及跨越天体物理和空间物理的多学科合作。我们的项目还整合了研究和教育方面的努力。这项研究正在为毕业论文做出贡献，本科生正在接受实地和实验室的培训。