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 ...
