Archaeomagnetic dating

Archaeomagnetic dating relies on the measuring the orientation of iron particles in burnt deposits towards the magnetic pole.The pole moves around, but magnetised deposits stay fixed on its position at the time of burning.Then the discs and the small blocks of soil attached beneath them are carefully removed.

In order to harden the clay permanently, one must heat it above a certain temperature (the Curie point) for a specified amount of time.This correlation process is called magnetostratigraphy. Lava, clay, lake and ocean sediments all contain microscopic iron particles.When lava and clay are heated, or lake and ocean sediments settle through the water, they acquire a magnetization parallel to the Earth's magnetic field.We can measure the difference between their orientation and the present position of the pole, which can give us the date of the burning episode.

When material such as clay or earth is heated to above 650 degrees Celsius (the Curie Point), such as in a hearth or kiln, the existing magnetism of iron particles in the soil is wiped clean and they are re-magnetised.The term that refers to changes in the Earth's magnetic field in the past is paleomagnetism.


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