The International geological organization has decided to name a geological age represented by a 770,000-year-old stratum discovered near Tokyo "Chibanian."
A group of scientists, including those at Ibaraki University and the National Institute of Polar Research, filed a request with the International Union of Geological Sciences to register the stratum as a site representing a geological age.
The scientists said the stratum provides evidence of the Earth's most recent switching of its north and south geomagnetic poles.
The International Union of Geological Sciences voted for the registration of the stratum on Friday in the organization's executive board meeting held in South Korea.
It decided to name the geological age "Chibanian" after Chiba Prefecture, where the stratum was discovered. The period spans from about 770,000 years ago to about 120,000 years ago.
Geologists divide the Earth's 4.6 billion-year history into 117 geological ages. This is the first time for a stratum in Japan to be recognized as representing such an age.
During the Chibanian age, important events in the Earth's history took place such as the birth of modern human beings -- homo sapiens.
High school textbooks are expected to have references to the "Chibanian" age.