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The Earth's magnetic field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons. Reversal occurrences are statistically random.
The polarity of the Earth's magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetism to track the past motion of continents.
A polarity chron, or in context chron, [4] is the time interval between polarity reversals of Earth's magnetic field. [5] It is the time interval represented by a magnetostratigraphic polarity unit. It represents a certain time period in geologic history where the Earth's magnetic field was in predominantly a "normal" or "reversed" position.
The Earth's magnetic field is approximately four times stronger today than it was during the Gauss–Matuyama reversal. [4] The reversal is thought to have weakened the shielding that the magnetic field provides the surface Earth, resulting in more exposure to ionizing radiation generated by the early Pleistocene supernova , and leaving the ...
Subduction polarity reversal is a geologic process in which two converging plates switch roles: The over-lying plate becomes the down-going plate, and vice versa. There are two basic units which make up a subduction zone .
Earth's magnetic polarity reversals in last 5 million years. Dark regions represent normal polarity (same as present field); light regions represent reversed polarity. Magnetostratigraphy uses the polarity reversal history of Earth's magnetic field recorded in rocks to determine the age of those rocks.
The Brunhes–Matuyama reversal, named after Bernard Brunhes and Motonori Matuyama, was a geologic event, approximately 781,000 years ago, when the Earth's magnetic field last underwent reversal. [ 1 ] [ 2 ] Estimations vary as to the abruptness of the reversal.
A geomagnetic excursion, like a geomagnetic reversal, is a significant change in the Earth's magnetic field.Unlike reversals, an excursion is not a long-term re-orientation of the large-scale field, but rather represents a dramatic, typically a (geologically) short-lived change in field intensity, with a variation in pole orientation of up to 45° from the previous position.