Maori ovens yield data on Earth’s magnetic field

BBC : A researcher in New Zealand is searching for abandoned Maori steam ovens, called hangi, in order to gather data on Earth’s magnetic field. Gillian Turner of Victoria University in Wellington spoke at the annual meeting of the American Geophysical Union, held this week in San Francisco. The ovens, which date back to about AD 1200, were pits in the ground filled with stones that were heated to very high temperatures for cooking food. The stones the Maori used tended to have a high concentration of magnetite, which became demagnetized as they were heated past their Curie temperature. As they cooled, they became remagnetized in the direction of the local field, writes Jonathan Amos for the BBC. Using radiocarbon analysis of the charcoal left by the firewood burned, Turner and her team are working to gather data on Earth’s magnetic field in the South Pacific from the past 800 years. Her ultimate goal is to gather data that covers the past 10 000 years, but to go deeper in time, she will need to find other sources, such as volcanic rocks and lake sediments.