The Big Questions: Physics by Brooks Michael

Author:Brooks, Michael [Brooks, Michael]
Language: eng
Format: mobi, epub, azw3
Publisher: Quercus
Published: 2012-01-04T16:00:00+00:00

For a period of time, during a reversal there is no clearly defined field. So, could this happen with the Earth’s magnetic field, with potentially disastrous results? Unfortunately, even these simulations have not yet proved accurate enough for us to make forecasts for the Earth’s field. The best we can do, it seems, is to look at the evidence frozen into the planet’s rocky crust, and try to extrapolate our findings.

Written in the rocks

In the molten rock that pours from volcanoes and the gaps between tectonic plates in mid-ocean ridges, magnetic crystals – tiny grains of magnetite, for example – are free to move, and will orient themselves to the direction of the Earth’s magnetic field. When that rock cools, that orientation is frozen in, creating a rock whose magnetic field points towards its era’s magnetic north. By dating rocks and noting their magnetic orientation, researchers can build up a picture of how the direction of ‘north’ has changed over millennia. This is how we gained the first evidence for a shield failure. In 1904, geomagnetic studies of the Massif Central mountains of southern France revealed that the orientation of the magnetic crystals in the rocks was significantly shifted from what it would be today. In the 1920s, similar observations were made across the world, and the field of palaeomagnetism was born.

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