Apparent polar wander
Encyclopedia
Apparent polar wander is the imaginary movement of the Earth
's magnetic pole
s relative to a continent
while regarding the continent being studied as fixed in position, as determined by paleomagnetic
data. It is used in the study of plate tectonics
to interpret how continents move, join and split as they drift across the Earth's surface.
Apparent polar wander can be displayed on a map as an apparent polar wander curve: a line tracing the path of the magnetic pole throughout a given time period which is superimposed on a fixed representation of a continent. In reality it is unlikely that the magnetic poles wander significantly away from the geographic poles of the Earth, although they do undergo periodic geomagnetic reversal
, because theory shows that the Earth's magnetic field remains aligned to the Earth's rotational axis when averaged over time. Instead the continents drift across the surface of the Earth, driven by the mechanisms of plate tectonics. Although an apparent polar wander curve does not show the real situation, it has the advantages of not implying knowledge of the historical longitude
of continents, which is difficult to determine, and allows the motions of more than a single continent to be displayed clearly on a single diagram.
Apparent polar wander curves can show how a supercontinent
breaks up. Two or more joined continents will have the same or similar curves until they split, at which point the curves diverge. Conversely the curves can be used to show how landmasses come together in the process of supercontinent formation.
.
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's magnetic pole
Poles of astronomical bodies
The poles of astronomical bodies are determined based on their axis of rotation in relation to the celestial poles of the celestial sphere.-Geographic poles:...
s relative to a continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
while regarding the continent being studied as fixed in position, as determined by paleomagnetic
Paleomagnetism
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of...
data. It is used in the study of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
to interpret how continents move, join and split as they drift across the Earth's surface.
Apparent polar wander can be displayed on a map as an apparent polar wander curve: a line tracing the path of the magnetic pole throughout a given time period which is superimposed on a fixed representation of a continent. In reality it is unlikely that the magnetic poles wander significantly away from the geographic poles of the Earth, although they do undergo periodic geomagnetic reversal
Geomagnetic reversal
A geomagnetic reversal is a change in the Earth's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse...
, because theory shows that the Earth's magnetic field remains aligned to the Earth's rotational axis when averaged over time. Instead the continents drift across the surface of the Earth, driven by the mechanisms of plate tectonics. Although an apparent polar wander curve does not show the real situation, it has the advantages of not implying knowledge of the historical longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
of continents, which is difficult to determine, and allows the motions of more than a single continent to be displayed clearly on a single diagram.
Apparent polar wander curves can show how a supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
breaks up. Two or more joined continents will have the same or similar curves until they split, at which point the curves diverge. Conversely the curves can be used to show how landmasses come together in the process of supercontinent formation.
Development of the technique
The technique was first developed by Creer et al. in 1954. At this time plate tectonics was not the dominant theory it is now and it was thought that APW curves represented the rotation of the entire Earth relative to its axis of rotation, a hypothesis known as true polar wanderTrue polar wander
True polar wander is a solid-body rotation of a planet or moon with respect to its spin axis, causing the geographic locations of the North and South Poles to change, or "wander". In a stable state, the largest moments of inertia axis is aligned with the spin axis, with the smaller two moment of...
.