Determination of the intensity of the Earth´s magnetic paleofield by analysis of fossil magnetotactic bacteria

磁发电机的产生和演化关键取决于行星体的热历史。到目前为止，在地球热演化的模型中存在相当大的分歧。模型的约束条件可以通过从古地磁测量重建地球磁场来设置。不幸的是，随着年龄的增长，适合于古地震烈度研究的岩石数量急剧下降，前寒武纪虚拟偶极矩的计算也存在相当大的不确定性。因此，获得关于磁场存在和强度的独立信息至关重要，这不是基于古地磁信号的保存。我们建议从趋磁细菌的化石遗骸中获得这种独立的信息，趋磁细菌的存在只有在足够强的磁场存在下才有可能。在晚太古代的叠层石石灰岩中发现了可能的趋磁细菌化石。如果这些发现得到证实，它们提供了一种探测当时磁场的新方法，可以与古地磁数据进行交叉检查。因此，我们计划对地球上最古老的沉积岩中趋磁细菌化石遗骸的存在进行系统的调查，并根据其特征磁性推断其存在时的磁场强度。我们将利用最新的进展，在化石趋磁细菌的检测使用磁性测量筛选一个大集合的前寒武纪碳酸盐岩和硅质岩叠层石结构。

The onset and evolution of a magnetic dynamo depends critically on the thermal history of a planetary body. Until now, there is considerable disagreement in models for the thermal evolution of the Earth. Model constraints can be set by the reconstruction of the Earth s magnetic field from paleomagnetic measurements. Unfortunately, the number of rocks suited for paleointensity studies drops precipitously as we move back in age, and Precambrian virtual dipole moment calculations suffer from considerable uncertainties. Therefore, it is crucial to obtain independent information on the existence and strength of a magnetic field, which is not based on the preservation of a paleomagnetic signal. We propose to obtain such independent information from fossil remains of magnetotactic bacteria, whose existence is possible only in presence of a sufficiently strong magnetic field. Putative fossil remains of magnetotactic bacteria have been found in Late Archean stromatolitic limestones. If these findings are confirmed, they provide a new way of probing the magnetic field at that time, which can be cross-checked with paleomagnetic data. Therefore, we plan to conduct a systematic investigation for the occurrence of fossil remains of magnetotactic bacteria in the Earth s oldest sedimentary rocks and to deduce from their characteristic magnetic properties the intensity of the magnetic field at the time of their existence. We will take advantage from the recent advances in the detection of fossil magnetotactic bacteria using magnetic measurements to screen a large collection of Precambrian carbonates and cherts with stromatolite structures.