Stirring stuff

 作者:綦颗     |      日期:2019-03-07 04:10:03
By Mark Schrope AFTER decades of trying, researchers have finally recreated the effect that is thought to produce the Earth’s magnetic field. The centre of the Earth is believed to consist of a solid inner core surrounded by a fluid outer core of molten iron and nickel. The core is too hot to create a permanent magnetic field like that in a bar magnet. So early this century, researchers proposed the dynamo theory, which suggests that when liquid metal such as the material that forms the outer core flows under certain conditions,