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Paleomagnetism: Definition and Meaning
Paleomagnetism helps to investigate the past direction, magnitude, and polarity of the earth's magnetic field, since during the formation of rocks, they lock in the record of the direction and intensity of the magnetic field. Paleomagnetic data has played an instrumental role in deciphering the history of our planet, giving supporting evidence for continental drift and global and regional plate tectonics.
Historical background
Geophysicists who specialize in paleomagnetism are called paleomagnetists. In 1849, French physicist Achilles Delesse observed that certain minerals in rocks positioned themselves in line with the earth’s magnetic field, in a way that tiny compasses were placed in the rocks. Later, in 1906, French physicist Bernard Brunhes observed that some rocks exhibit the exact reverse position of the magnetic properties. In the 1940s, a system for measuring the minute magnetic field in the magnetic minerals was invented by the British physicist, Patrick M.S. Blackett, which earned him the Noble Prize in 1948.
Magneto Stratigraphy
The geochronological correlation technique is used to date volcanic and sedimentary rock sequences using the record of geomagnetic reversals preserved in them. With this method, the Remnant Magnetic Signature (RMS) is measured. Remnant Magnetic Signature is the magnetic field of the rock that gives insights to the magnetic property of earth of the particular period.
Paleomagnetic Isochrones
Paleomagnetic isochrones are the imaginary lines joining the rocks having similar magnetic properties. Paleomagnetic isochrones that are found along the Mid-Oceanic Ridge of the Atlantic Ocean cite decisive evidence for the continental drift as well as sea-floor spreading. Evidently, the rate of sea floor spreading has been calculated by using the age of isochrones and the distance between them.
On moving away from the newly formed relief of the mid-oceanic ridge, the adjacent rocks exhibit an exact reversal of magnetic properties, namely Brunhes, Matuyama, Gauss, and Gilbert, where the latter is the oldest.
Features
The geo-magnetic reversal of the minerals in the rocks is evident.
On either side of the mid-oceanic ridge, normal and reversal anomalies in the magnetic field are found.
Paleomagnetic isochrones exhibit complete parallelism.
Paleomagnetic epochs and events for 4.5 million years were calculated using the parallelism in the time sequence.
Conclusion
On studying the age and width of magnetic strips using paleomagnetism, the average rate of shifting of the geomagnetic poles can be predicted. Under-water navigation and mining using location-dependent signatures is an interesting application of palaeomagnetism in recent times.
Frequently Asked Questions
What is Paleomagnetism?
Paleomagnetism is the study of the fossil magnetism in rocks, sediments, or archaeological materials used to determine the past configurations of the continents.
What is Remnant Magnetic Signature?
Remnant Magnetic Signature is the magnetic field of the rock that gives insights to the magnetic property of earth of the particular period.
What is Paleomagnetic isochrones?
Paleomagnetic isochrones are the imaginary lines joining the rocks having similar magnetic properties. Paleomagnetic isochrones that are found along the Mid-Oceanic Ridge of the Atlantic Ocean cite decisive evidence for the continental drift as well as sea-floor spreading.
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