Book contents
- Frontmatter
- Contents
- Preface to the second edition
- Preface to the first edition
- Preface to the English edition
- 1 Heat from within
- 2 At the time of the Earth’s birth
- 3 Formation of the layered structure of the Earth
- 4 Time scale of the Earth’s evolution
- 5 Plate tectonics revolution
- 6 Evolution of the mantle
- 7 Origin of the atmosphere and oceans
- 8 Isotopes as DNA of nature
- 9 The Earth’s magnetism
- 10 The Moon
- 11 The past and future of the evolving Earth
- References
- Index
9 - The Earth’s magnetism
Published online by Cambridge University Press: 05 May 2012
- Frontmatter
- Contents
- Preface to the second edition
- Preface to the first edition
- Preface to the English edition
- 1 Heat from within
- 2 At the time of the Earth’s birth
- 3 Formation of the layered structure of the Earth
- 4 Time scale of the Earth’s evolution
- 5 Plate tectonics revolution
- 6 Evolution of the mantle
- 7 Origin of the atmosphere and oceans
- 8 Isotopes as DNA of nature
- 9 The Earth’s magnetism
- 10 The Moon
- 11 The past and future of the evolving Earth
- References
- Index
Summary
MAGNETIC MINERALS IN ROCKS: SMALLER IS BETTER
As mentioned in Chapter 5, paleomagnetic studies suggest that remanent magnetization imprinted on volcanic rocks has been preserved for hundreds of millions of years without changing its direction and intensity. How can such remarkable stability be possible? To answer this question, we first need to introduce some basic concepts of rock magnetism. Magnetic materials such as iron, nickel, and iron oxide (typically magnetite) are said to be ferromagnetic, meaning that when subjected to an external magnetic field, they are magnetized strongly in parallel to the magnetic field. Even after the removal of the applied magnetic field they still retain a noticeable amount of magnetization, which is called remanent magnetization.
Ferromagnetism is retained only below the critical temperature known as the Curie temperature. This phenomenon was discovered by the French physicist Pierre Curie (the husband of Marie Curie). For example, the Curie temperatures of iron, nickel, and magnetite are 770 °C, 358 °C, and 585 °C, respectively. Above the Curie temperature, ferromagnetism disappears, and these materials no longer exhibit magnetization.
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- Information
- The EarthIts Birth and Growth, pp. 104 - 112Publisher: Cambridge University PressPrint publication year: 2012
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