There is no pattern to these changes, which seem to take place at random. Chrons last from between 0.1 and 1million years (see diagram) with an average of 450,000 years. Most reversals take between 1,000 and 10,000 years to happen.
The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago; and may have happened very quickly, within a human lifetime. A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period. That reversal lasted only about 440 years with the actual change of polarity lasting around 250 years. During this change the strength of the magnetic field weakened to 5% of its present strength. Brief disruptions that do not result in reversal are called geomagnetic excursions.
The past record of geomagnetic reversals was first noticed by observing the magnetic stripe reversals on the ocean floor. This soon led to the development of the theory of plate tectonics. The relatively constant rate at which the sea floor spreads causes "stripes" in the basalt. From these past magnetic fields polarity can be inferred. Data is got by towing a magnetometer along the sea floor.
No existing unsubducted sea floor is more than about 180 million years old, so other methods are used for detecting older reversals. Most sedimentary rocks have tiny amounts of iron rich minerals. Their orientation reflects the magnetic field when they formed. The rocks keep that record unless they get changed by some later process.
A "superchron" is a polarity interval lasting at least 10million years. There are two well-established superchrons, the Cretaceous Normal and the Kiaman.
The Cretaceous Normal (also called the Cretaceous Superchron or C34) lasted for almost 40million years. Between the Cretaceous Normal and the present, the frequency has generally increased slowly.
The Kiaman Reverse Superchron lasted from the late Carboniferous to the late Permian. That is more than 50million years, from 312 to 262 million years ago (mya). The magnetic field had reversed polarity. The name "Kiaman" derives from the Australian village of Kiama, where some of the first geological evidence of the superchron was found in 1925.
The magnetic field of the Earth, and of other planets that have magnetic fields, is caused by dynamo action of molten iron in the planetary core. This convection (movement) generates electric currents which in turn give rise to magnetic fields. In simulations of planetary dynamos, reversals occur from the underlying dynamics. For example, Gary Glatzmaier and collaborator Paul Roberts of UCLA ran a numerical model of the coupling between electromagnetism and fluid dynamics in the Earth's interior. Their simulation reproduced key features of the magnetic field over more than 40,000 years of simulated time and the computer-generated field reversed itself. Global field reversals at irregular intervals have also been observed in a laboratory liquid metal experiment VKS2.
As far as we know, there is no effect on life. Studies have been done to see if reversals relate in any way to extinction events. Statistical analysis shows no evidence for a correlation between reversals and extinctions.
Chron
A chron is a general term in Earth science. It means a period of time, usually less than a million years.
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Root (disambiguation)
Root may refer to:
Root of a function
In mathematics, a root of a function "f" is a number x that turns the value of "f" to 0:
Because polynomials are also functions, roots are real things.
The fundamental theorem of algebra says every polynomial with complex coefficients has at least one (complex) root. Using the fundamental theorem of algebra and the polynomial remainder theorem together shows that every complex polynomial of degree "n" has exactly "n" complex roots, and some of them may be equal.
De Moivre's formula
In mathematics, de Moivre's formula or de Moivre's theorem is an equation named after Abraham de Moivre. It states that for any real number "x" and integer "n",
formula_1
The formulation of De Moivre's formula for any complex numbers formula_2 (with modulus formula_3 and angle formula_4) is as follows:
formula_5
Here, formula_6 is Euler's number, and formula_7 is often called the polar form of the complex number formula_2.
The formula is very important because it connects complex numbers and trigonometry. It can be proved using the trigonometry form of complex numbers by mathematical induction, with the help of some trigonometrical identities. It can also be proved using Euler's formula as well.
By using this formula, any equation of the form formula_9, where "w" is complex, can be solved.
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Jon English
Jonathan James "Jon" English (26 March 1949 – 9 March 2016) was an English-born Australian singer, songwriter, musician and actor. He was an early member of the band Sebastian Hardie. He played the role of Judas Iscariot in the Australian production of the stage musical "Jesus Christ Superstar" in 1972. He also performed in Gilbert and Sullivan's operettas "The Pirates of Penzance", "The Mikado" and "H.M.S. Pinafore" from 1984. He also acted in a number of television series. As a solo singer, his best known songs were "Turn the Page", "Hollywood Seven", "Words are Not Enough", "Six Ribbons" and "Hot Town".
English was born in Hampstead, London. He moved to Sydney as a child in 1961. He had four children. He was a fan of the Parramatta Eels.
English died from an aortic aneurysm caused by surgery problems on 9 March 2016 in Newcastle, New South Wales. He was 66.
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Beechcraft Super King Air is a modern variant.
Beechcraft King Air are known in the US Army as U-21 Ute, for light transport duties. In US Navy it known as T-44 Pegasus, a trainer.
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The company was previously named Eurocopter. The name change was made 1 January 2014. It's a part of the Airbus company.
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