Newly Named Chibanian Age Demarcates Earth’s Last Magnetic Flip

The time period, which spans 770,000 to 126,000 years ago, started with a reversal of the planet’s magnetic field.

kerry grens
| 2 min read
chibanian chiba prefecture japan yoro river earth magnetic field reversal polarity kazusa

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ABOVE: The Yoro River in Chiba Prefecture, Japan, has mineral deposits that document a reversal in the Earth’s magnetic field, which marked the start of the Chibanian.
© ISTOCK.COM, VOYATA

The International Union of Geological Sciences has designated the time in Earth’s history from 770,000 to 126,000 years ago as the Chibanian, notable for being the most recent reversal of the planet’s magnetic poles, The Japan Times reported January 17. It’s named for the Chiba Prefecture in Japan, where a deposition of minerals and marine fossils reveals the flip in polarity that occurred at the start of the Chibanian.

According to The Washington Post, iron within minerals of the deposition aligned with Earth’s magnetic field at the time the rocks cooled from a molten form, logging the field’s change in polarity. “This sedimentary sequence, called the Kazusa Group, has a total thickness of 3 kilometers with an anomalously high deposition rate ...

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Meet the Author

  • kerry grens

    Kerry Grens

    Kerry served as The Scientist’s news director until 2021. Before joining The Scientist in 2013, she was a stringer for Reuters Health, the senior health and science reporter at WHYY in Philadelphia, and the health and science reporter at New Hampshire Public Radio. Kerry got her start in journalism as a AAAS Mass Media fellow at KUNC in Colorado. She has a master’s in biological sciences from Stanford University and a biology degree from Loyola University Chicago.

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