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

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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.