The discovery of bricks engraved with the names of Mesopotamian kings dating back several millennia B.C. BC has highlighted the existence of an unusual period of very high magnetic field intensity between the years -1050 and -550.
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[EN VIDÉO] Geomagnetism or the secrets of earth magnetism The magnetism present everywhere on earth has fascinated people for a long time. Before its creation…
Since its formation, the Earth has been surrounded by a strong magnetic field, which can be imagined as a gigantic dipole on a planetary scale. This field created by the Earth's core protects us from the sun's harmful radiation. However, we know that neither its intensity nor its direction has been constant over time. This can be seen in certain rocks that can record the properties of this magnetic field at a given time. This is particularly true for volcanic rocks.
These are actually formed by the cooling and crystallization of a magma magma. When it reaches the surface and cools, the ferromagnesian minerals it contains “store” the intensity and direction of the surrounding magnetic field. The subsequent analysis of these volcanic rocks thus makes it possible to reconstruct the properties of the magnetic field and its variations over geological time. This is called paleomagnetismpaleomagnetism.
Terracotta stones that reveal the history of the Earth's magnetic field
This ability of rocks to “record” the orientation of the magnetic field is also very useful in archeology. It allows the identification of buried human artifacts, particularly ceramics or terracotta bricks. The magnetism of these artifacts can also be used to better understand the history of the magnetic field. One then speaks of archaeomagnetism.
This happened when examining these Mesopotamian-era bricks found in Iraq. They have the peculiarity that when they were made, the names of the ruling kings were engraved, which allowed archaeologists to date them precisely to the Iron Age, i.e. between the 3rd and 1st millennium BC. BC, to date. The properties of the magnetic field of this period were thus captured by the iron oxides present in the bricks at the time of firing.
The detection of a period of high intensity of the magnetic field
The results of these analyzes were published in the scientific journal PNAS. In particular, they made it possible to confirm the existence of a very particular magnetic anomaly known as the “Levantine Iron Age geomagnetic anomaly”. Previous studies at sites in China, Bulgaria and the Azores had actually hypothesized that there was an unusually strong magnetic field between the years -1050 and -550.
A hypothesis supported by these new results, which also allow a precise dating of this period of high intensity. In addition, the data shows that the magnetic field changed during the reign of King Nebuchadnezzar II between 604 and 562 B.C. BC changed dramatically in a very short time, which illustrates the possibility of such a very rapid development of the geomagnetic sphere.