Investigating the chronological relationship of different strata or measuring their ages is called chronology. The Earth's magnetic field has repeatedly reversed. In many cases, strata contain a record of the magnetic field at the time they were formed (natural remanent magnetism), and by measuring the ages and magnetization of many strata, a "time scale of geomagnetic reversals" has been created that records the history of geomagnetic reversals. Geomagnetic chronology is a method of chronology that uses the time scale to measure the magnetic state of each strata. For some time, a method called geological chronology has been used to determine the relative temporal relationships of distant strata using widely distributed fossils. Source: Heibonsha World Encyclopedia, 2nd Edition Information |
各地層の年代的上下関係を調べたり,あるいは年代を測定することを編年という。地磁気は逆転を繰り返してきた。地層には,それが形成されたときの地磁気が記録されている場合が多く(自然残留磁気),地層の年代と地層の磁化のようすを多数測定することにより地磁気逆転の歴史を記録した〈地磁気逆転のタイムスケール〉が作られている。地磁気編年とは各地層の磁気のようすを測定し,このタイムスケールを利用して行う編年をいう。 以前より,地質編年といって,広く分布する化石を利用し,互いに離れた地層の時間的上下関係を相対的に決定することが行われてきた。
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