古强度数据的可靠性评估研究

The geomagnetic field is important for life on Earth: it protects our planet from harmful solar radiation, which would interfere with our satellite communications and power infrastructure, it may potentially have a significant influence on climate, and is also likely to have played a key role for early life on Earth. However, despite being one of the oldest known features of Earth, many aspects of how the field is generated and how it has evolved over time are poorly understood..The geomagnetic field has been highly variable over geological time. Two extreme examples are superchrons, where the magnetic fields polarity remained constant for 10’s of millions of years and the field strength (paleointensity) was thought to be unusually high, and archeomagnetic spikes, where paleointensity can reach twice as strong as the present day and change at rates 10 times faster than anything that has been directly observed. Such dramatic observations, however, remain controversial due to ambiguities in the data available (sites of similar ages, but from different studies, often yield distinct results). .Part of this ambiguity arises from the diverse nature of a paleointensity data, where analyses of long term trends rely on data measured using multiple methods. Unfortunately, there are no systematical studies that explore how different methods influence the final results obtained. This is largely due to the time consuming nature of undertaking a paleointensity experiment, which makes such and extensive study impractical. Recent numerical simulations, however, strongly suggest that the four main paleointensity methods, which were often assumed to yield equivalent results, can behave very differently, even under the most ideal of conditions..In this project, I will use a combined experimental and theoretical approach to provide the first, and most detailed analysis of paleointensity methods. The work will obtain an extensive experimental data set from several different paleointensity methods. This will be the largest-to-date data set of this type, which will allow a comprehensive comparison and statistical analysis of how the different methods influence the final results. Such an extensive data set would be unique in the history of paleointensity studies and would have great potential for yielding invaluable insight into paleointensity data and advances on current methods..These new data will then be combined with magnetic theory to expand our ability to realistically simulate paleointensity results. This will bring together, for the first time, magnetic theories of alternating field demagnetization, thermoremanent and anhysteretic remanent magnetizations to establish state-of-the-art paleointensity models. Such models are necessary to generate the large amounts data necessary to systematically explore paleointensity methods and how they impact our interpretations of geodynamo behavior over geologic time.

地磁场对地球上的生命起着至关重要的作用。地磁场不仅保护地球生物免受太阳风和宇宙射线的侵袭，而且在维护地球环境稳定中扮演重要角色。但是，目前对于地磁场的起源和演变还缺乏深入认识，造成这种现象的主要原因之一就是难于获得准确的古地磁场强度数据。不同实验方法产生强度数据的多样性是造成古地磁强度数据不确定性的原因之一。但是，目前关于不同实验方法对强度最终结果产生何种影响还缺乏系统研究。.本项目将采用实验和模拟分析相结合的研究方法，系统研究并评估不同实验方法对古强度结果产生的影响。利用不同的强度测量方法获得多组数据，通过综合对比分析来研究不同方法对最终结果的影响，结合基于磁学理论的模拟研究，进一步提高古强度结果的可靠性。本项目还将结合交变退磁、热剩磁和非磁滞剩磁的磁学理论，进而建立先进的古强度模型。本项目研究结果将为探索古强度数据的可靠性以及解释地质时期地球动力学的机制提供可靠的数据支持。

地磁场古强度研究有助于回答地球演化历史相关的重大科学问题，同时又是古地磁领域极具挑战性的工作。该项目致力于对古强度实验分析方法提出新的认识，并建立新的古强度实验材料筛选标准，从而获得精确的古强度结果，为认识地磁场演化历史提供依据。受该项目支持，目前已发表11篇论文（其中3篇项目负责人为第一作者），部分论文发表在Proceedings of the National Academy of Sciences (PNAS)、National Science Review等高水平综合期刊上。.在该项目的支持下，我们提出了一种新的预测样品是否适合古强度实验的方法。通过对特定样品进行重复实验，发现样品的基本磁学性质与其在强度实验中的表现存在相关性。该方法可用于实验前样品筛选，并可用来分析判断已发表强度数据的可靠性。.该成果发表在PNAS上，长期以来样品岩石磁学性质和古强度结果之间的关系一直受关注，但之前一直没有建立明确的关系，我们的结果是古强度研究中的一个重要突破。.该成果被应用到中国近几千年及白垩纪超静磁期(CNS)以来地磁场强度研究中。白垩纪超静磁期地磁场强度的研究涉及到地磁场强度与地磁倒转频率之间关系的科学问题。之前有研究提出二者之间存在关系，但由于数据质量和可靠性参差不齐，该问题一直存在争议。我们的工作旨在探讨古强度研究方法和数据可靠性这一根本问题，为讨论上述科学问题提供了一种广泛接受的分析方法。