The Institute for Marine Resources and Environment, a division of the National Institute of Advanced Industrial Science and Technology ( AIST) has discovered that the direction and strength of the earth's magnetic field have a periodic component of about 100,000 years. Because this periodicity corresponds to the period of both changes in the eccentricity of the earth's orbit and the glacial/interglacial periods, it is clear that there is a relation between these variations and the earth's magnetic field. It had previously been believed that the variations in the magnetic field were only related with the outer core, but it must now be understood within the context of all variations in the earth system.

These results appear in the March 29 edition of the journal "Science."

• It had previously been believed that magnetic field variations had not a long-term component of longer than about 10,000 years.
  
  The magnetic field originates from and is maintained by fluid flows in the earth's outer core. It had been believed to be independent of other fields, and it was predicted from the physical properties of the outer core that there would not be a long-term component of longer than about 10,000 years.


• However, the AIST has discovered records in marine sediments that show a long-term periodic component of 100,000 years in variations in the past magnetic field.
  
  Using a high-sensitivity magnetometer to measure remanent magnetization of marine sediments, we obtained a continuous record of variations in strength and inclination of magnetic field that have occurred in the past 2.3 million years. Frequency analysis of this record has led to the discovery of a long-term periodic component of 100,000 years.
   
• It is clear now that magnetic field variations must be understood within the context of variations in the earth system.
  
  The 100,000-year period of variation corresponds with variation in the eccentricity of earth's orbit and the period of the glacial/interglacial cycles. Therefore, magnetic field changes must be understood within the context of variations in the earth system.
  
  To understand the mechanism of this 100,000-year period of variation, we plan to collect and analyze data from a larger number of locations. Furthermore, we will consider the geomagnetic field as one of the basic environments of the Earth, and investigate possible relation between the geomagnetic field and the biosphere including human being.