Why does the earth's magnetic field change its polarity??
Who has not played explorer and tried to orientate himself with a compass? Since the 15. In the sixteenth century, the orientation property of these small magnetized needles was well known to seafarers. It reflects the existence of the earth's magnetic field reflect, which in addition to a reliable orientation, protects the earth and its biosphere from solar radiation. However, the magnetic field of the Earth is anything but stable. The magnetic poles are in fact not fixed and their position changes over the years until they are reversed.
These reversals of the magnetic field, when the north pole becomes the south pole and vice versa, have occurred hundreds of times in the history of the Earth. But why does the magnetic field reverse episodically?? What is the origin. The engine of these reversals?
What is the magnetic field of the earth?
Let us imagine a large dipole magnet placed in the center of the Earth. The magnetic lines of force generated by this magnet represent what is known as the Earth's magnetic field. These lines of force intersect the Earth's surface at an angle that varies with latitude. They "enter" vertically at one point, is called the north magnetic pole, and emerge in the same way at the south magnetic pole. At the magnetic equator the field lines are horizontal. Currently, the magnetic axis is offset from the Earth's rotational axis, which means that the magnetic and geographic poles do not coincide. The magnetic north pole is currently located in Siberia and the magnetic south pole in Terre Adelie, off Antarctica.
The origin of the magnetic field of the Earth
If the image of a large dipolar magnet at the center of the Earth allows a first approximation to understanding the magnetic field, its origin is much more complex. Everything takes place at the level of the Earth's core, which acts like a self-sustaining dynamo. Due to temperature variations with depth, of the earth rotation and the Coriolis forces the liquid iron that forms the outer core flows with strong convection currents structured in swirling columns parallel to the Earth's rotation axis. It is this strong convective motion that creates a dynamo effect that gives rise to the magnetic field.
Magnetic field reversals over time
In the early 1900s, scientists discovered that rocks of volcanic origin had different directions of magnetization. Some measurements showed magnetization in the same direction as the current magnetic field, while others showed completely opposite magnetization, resulting in "magnetic anomalies" emerged. These observations gave rise to the idea that the Earth's magnetic field could reverse episodically. This hypothesis has been corroborated over time, and there are now scales of magnetic polarities that record and date the various reversals in Earth's history.
These scales define periods of "normal" polarity when the measured field is identical to the current field, and periods of "reverse" polarity when the measured field is in the opposite direction. It is clear that the reversals are neither regular nor of equal duration. The time intervals corresponding to a stable polarity (normal or reversed) are called chrons and are numbered starting from the current (C0). The duration of each chronicle is extremely variable, ranging from less than a million years to tens of millions of years (called a superchronicle). Also their frequency is very chaotic. The magnetic field has reversed about 300 times in the last 200 million years. The last inversion took place before 773.000 years takes place.
The origin of the reversals of the Earth's magnetic field
The measurements show that the poles are not fixed, but moving. In the last twenty years, the north pole has moved several hundred kilometers and is currently moving about 55 km/year. On the other hand, the south pole moves only 10 km/year. These variabilities mean that the two magnetic poles are not necessarily at opposite ends of the Earth. It is related to the complex Dynamics of the magnetic field together, which is not only dipolar, but has multipolar components. This multipolarity is related to the movements of liquid iron in the earth's core. Disturbances in the nucleus can alter the convective structures and create secondary magnetic loops that add to the main dipole. This multipolar component would be able to temporarily weaken the Earth's dipole, resulting in either a complete reversal of the magnetic field or a restoration of the poles to their original position after a period of "excursion".
So, just before a reversal, the magnetic poles seem to follow complex and tortuous paths on the Earth's surface, associated with a drastic decrease in magnetic field strength, but without the field disappearing completely. However, the exact mechanisms associated with magnetic field inversions are still poorly understood, including the origin of disturbances in the Earth's core. In any case, a reversal seems to occur in a relatively short period of time (1).000 to a maximum of 20.000 years to occur.
So, is the current acceleration of the movement of the magnetic north pole equivalent to A short-term inversion? Nothing is less certain, because the south pole remains relatively stable. The current state of our knowledge does not allow us to predict when the next excursion or reversal will occur.