Researchers can now demonstrate that a short-lived change in the earth?s magnetic field really did take place about ten million years ago. Before this, they had evidence that the magnetic fields had reversed, but felt this could have been caused by chemical or physical processes that had altered the magnetic signals in the sediment they were studying.

The Netherlands Organization for Scientific Research announced that Utrecht University researchers have developed a better method of identifying the magnetic signals in old geological strata. Particles of iron in sediments orient themselves in accordance with the local magnetic field of the earth. As the sediment consolidates over the course of several decades, the particles of iron continue to lie in the direction of the original magnetic field. Thus they preserve the data on the state of the magnetic field that existed when the sediment was being deposited.

The researchers developed a method which gets information from the carriers of the magnetic signal in sediments, which include the iron oxides magnetite and hematite. In an organically rich layer in the eastern Mediterranean, they found that bacteria had formed organic material. With this new method, they can distinguish between this kind of bacterial material and the original magnetic signal.

Studies of the earth?s past magnetic field are important for our understanding of the ?geodynamo??the theory that the geomagnetic field is generated in the center of the earth. According to this theory, the electricity that runs through the molten iron of the earth?s outer core causes the magnetic field. The earth?s magnetic field now points south, meaning that a compass needle points north. Some 800,000 years ago, a compass needle would have pointed south, having previously pointed north.

The question is: What caused this reversal and will it happen again? And how will it effect us if it does?


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