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By tracking and cross-dating past changes in the location of the magnetic field, geophysicists have reconstructed a series of magnetic polar positions extending back more than 2,000 years. At archaeological sites, hearths constructed of iron-bearing clays are ideal for archaeolomagnetic sampling because they were subjected to repeated hot firings.
This series of dated positions is known as the "archaeomagnetic reference curve." (Stacey Lengyel, 2010.
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This means that although they are very similar chemically, they have different masses.
The total mass of the isotope is indicated by the numerical superscript.
A huge amount of work is currently underway to extend and improve the calibration curve.
Moving away from techniques, the most exciting thing about radiocarbon is what it reveals about our past and the world we live in.
The uncalibrated date is given with the unit BP (radiocarbon years before 1950).
The calibrated date is also presented, either in BC or AD or with the unit cal BP (calibrated before present - before 1950).
Radiocarbon dating was the first method that allowed archaeologists to place what they found in chronological order without the need for written records or coins.
In the 19th and early 20th century incredibly patient and careful archaeologists would link pottery and stone tools in different geographical areas by similarities in shape and patterning.
Now the curve extends (tentatively) to 50,000 years.