Scientist of the Day - Motonori Matuyama

Motonori Matuyama, a Japanese geophysicist, was born Oct. 25, 1884. In 1929, Matuyama made the rather bold suggestion that the Earth's magnetic field had once been reversed from its present orientation, so that at one time, a compass needle would have pointed south instead of north. His evidence came from igneous rocks in Japan and Manchuria, which indicated by their residual magnetic fields that, when they cooled millions of years ago, the Earth's north magnetic pole had been in the vicinity of the south geographic pole. As it turns out, the same suggestion had been made once before, by a French physicist, Bernard Brunhes, in 1905. Neither man made many converts, which is not surprising, since at the time the source of the Earth’s magnetic field was poorly understood, and radiometric dating was in its infancy. However, in 1959, it was proposed once again that the Earth's magnetic field reversed itself periodically, and by 1963 the evidence for it was being used to demonstrate the reality of sea-floor spreading and lay the basis for plate tectonics.

We now know that for the past .78 million years, the Earth's magnetic field has been normal (magnetic north being north), and that before this period, from 2.6 million to .78 million years ago, the magnetic field was reversed. The period between reversals is called a "chron", and the last chron before the present one, when the field was reversed, is called the Matuyama chron, in honor of our scientist of the day. The present chron is named the Brunhes chron, after the other early proponent of the idea of geomagnetic reversals. The last reversal, which occurred .78 million years ago, is called the Brunhes-Matuyama reversal. There were other chrons and other reversals before the Brunhes and the Matuyama, and they carry the names of Carl Friedrich Gauss and William Gilbert and other pioneers in the study of the earth's magnetism. We see above a simple chart that shows the last four chrons (second image). You will note that there are short-lived mini-reversals within each chron, such as the Jaramillo event within the Matuyama chron; the second chart (third image) shows how our understanding of the complexity of Earth’s magnetic reversals progressed in just the first decade of plate tectonics.

Matuyama’s paper appeared in the Proceedings of the Imperial Academy of Japan for 1929. We have this volume in the Library’s serials collection. There are very few portraits of Matuyama available, and all are of low resolution. We show you the best one we could find (fourth image).

Dr. William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to ashworthw@umkc.edu.