Motonori Matuyama (松山 基範 Matsuyama Motonori?, October 25, 1884 – January 27, 1958) was a Japanese geophysicist who was the first to surmise that the Earth's magnetic field had undergone reversals in the past. The era of reversed polarity preceding the current Brunhes era of normal polarity is called the Matuyama reversed chron and the boundary between them is called the Brunhes–Matuyama reversal.
Matuyama was born at Uyeda (now Usa) in Japan, the son of a Zen abbot. He was educated at the University of Hiroshima and Kyoto Imperial University, where he was appointed to a lectureship in 1913. After spending the period 1919–21 at the University of Chicago working with Thomas C. Chamberlin he was made professor of theoretical geology at Kyoto Imperial University. He conducted a gravity survey of Japan during the period 1927–32, extending this to also cover Korea and Manchuria, and studied marine gravity using the Vening–Meinesz pendulum apparatus in a submarine.
While rocks had earlier been found with polarities opposite to the present field and the hypothesis advanced that the field had reversed in the past, Matuyama was the first to conduct a disciplined study of the hypothesis. In 1926 he began collecting basalt specimens in Manchuria and Japan, and in 1929 published a paper showing that there was a clear correlation between the polarity and the stratigraphic position. He remarked that in the early Pleistocene the Earth's field had been reversed and that it had later changed to the present polarity. The period of reversed polarity, dating from , is now called the Matuyama reversed chron and the transition to normal polarity (like that of the present Earth's field) is the Brunhes-Matuyama reversal.
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