Japan-based name ‘Chibanian’ set to represent geologic age of last magnetic shift

The name “Chibanian,” based on a stratum discovered in Chiba Prefecture, is set to represent the geological age when the latest reversal of the Earth’s magnetic fields is believed to have occurred, a Japanese national research institute said Monday.

The National Institute of Polar Research said the term meaning “Chiba age” garnered more than 60 percent of votes, beating “Ionian,” a name related to stratums in Italy, for a geologic time period from 770,000 to 126,000 years ago in the first screening process at an international academic society.

Although the selection process is not over yet, Japanese researchers expect Chibanian to be formally adopted by the International Union of Geological Sciences by the end of next year, becoming the first name associated with a Japanese place to represent any geologic time period.

The Chiba stratum is exposed on a cliff in the city of Ichihara, along the Yoro River on the Boso Peninsula. In the stratum, minerals found in good condition clearly show that switching of north and south magnetic poles occurred 770,000 years ago.

In addition to minerals, the stratum is rich in fossils of microorganisms, including those of the sea, and volcanic ash, indicating the time when the stratum was deposited and changes in the environment back then, including the climate.

The Chiba stratum has been competing with two other stratums in Italy — one in Montalbano Jonico and another in Valle di Manche — to represent the period during which the Earth’s 11th switching of north and south magnetic poles took place.

“Our efforts bore fruit,” said Makoto Okada, a professor of paleomagnetic studies at Ibaraki University. “It’s a stratum on an unremarkable cliff, but we believe (the anticipated naming) will provide a good opportunity to people, especially children, to take an interest in Earth science.”

Boundaries in geochronology are established by composite sections with episodic depositions evidencing the planet’s 4.6 billion years of history, including drastic environmental changes.

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