Archaeomagnetic dating

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Secular variation dating using archaeomagnetic directions and archaeointensities has been used for Neolithic and younger cultures.Directional dating can sometimes be as good as ±25 years.Magnetism occurs whenever electrically charged particles are in motion.The Earth's molten core has electric currents flowing through it.On the earth's surface, when you hold a compass and the needle points to north, it is actually pointing to magnetic north, not geographic (true) north.The Earth's magnetic north pole can change in orientation (from north to south and south to north), and has many times over the millions of years that this planet has existed.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.

The curve has been well-documented for Britain, but in many other areas of the world there is a lot less certainty in using this technique.The term that refers to changes in the Earth's magnetic field in the past is paleomagnetism.Any changes that occur in the magnetic field will occur all over the world; they can be used to correlate stratigraphic columns in different locations.These differences in magnetic orientation, which can give us an accurate date, are compared to a known curve of the movement of the earth's magnetic pole.This is not always a straightforward process - the curve sometimes doubles back on itself in a wave pattern reflecting the back and forth movements of the pole over time - therefore a sample can apparently give two or more separate dates, sometimes centuries apart.

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