Paleomagnetism, Definition, Working, Significance, Diagram

The concept of palaeomagnetism was first introduced by French physicist Bernard Brunhes in 1906 to explore how volcanic rocks capture Earth's magnetic field direction upon cooling. The Earth's magnetic field is like a giant bar magnet that is slightly tilted from its rotational axis. It has north and south poles determined by the field line’s entry and exit points. 

Remarkably, the polarity of this field can be reversed, swapping the north and south poles. Magnetic minerals in rocks, such as magnetite, align with the magnetic field below the Curie temperature, causing the field's direction and intensity to be preserved at the time of formation. 

How Does Paleomagnetism Work?

Palaeomagnetism analyses the remnant magnetization of rocks caused by changes in the earth’s magnetism over time. This remnant magnetization refers to the permanent magnetization that rocks acquire as they cool and solidify from molten material or undergo chemical changes at low temperatures. 

Paleomagnetism Significance

The study of paleomagnetism not only helps us to understand the various geographical phenomena that happened in the past but with its study, we can make certain future geographical predictions.

• Predictions about the Earth's magnetic field change: It helps in understanding the past variations in Earth's magnetic field, which include countless reversals and flips (like polar wandering). By studying this, we can make informed predictions about the field's future behaviour.
• To understand the earth’s evolution: The study of palaeomagnetism is also known as fossil magnetism. It is an important source of information about the earth's evolution over time. Many rocks have kept this record since they were formed.
• Evidence supporting the plate tectonics theory: Paleomagnetism provides strong data supporting the hypothesis of plate tectonics. It records how magnetic minerals in the oceanic crust, particularly iron-rich basalt, align with the magnetic field, particularly along mid-ocean ridges, preserving the magnetic field's alignment at the time of formation.
• Documentation of magnetic field: It provides a detailed account of the direction of the Earth's magnetic field, with many rocks retaining this information since their origin.
• Dating rocks and fossils: Paleomagnetism can help date the origin of rocks, and magnetic reversals serve as a time scale for dating fossils found in certain rock layers.

Paleomagnetism: Earth’s Magnetism, Sea Floor Spreading and Plate Tectonics

Rocks contain tiny magnetic minerals that align themselves with the Earth's magnetic field when they form. By studying the orientation of these minerals, scientists can reconstruct the past positions of continents and the history of the Earth's magnetic field. Hence, palaeomagnetism acts as a proof for theories like seafloor spreading and plate tectonics.

Paleomagnetism UPSC PYQs

Consider the following:

1. Electromagnetic radiation
2. Geothermal energy
3. Gravitational force
4. Plate movements
5. Rotation of the earth
6. Revolution of the earth

Which of the above are responsible for bringing dynamic changes on the surface of the earth? (UPSC Prelims 2013)

1. 1, 2, 3 and 4 only
2. 1, 3, 5 and 6 only
3. 2, 4, 5 and 6 only
4. 1, 2, 3, 4, 5 and 6

Answer: (d)

Paleomagnetism FAQs

Q1. What is palaeomagnetism?

Ans. Palaeomagnetism is the study of Earth's ancient magnetic field, as recorded in rocks, sediments, and archaeological materials. It helps us understand how Earth's magnetism has changed over time.

Q2. How does palaeomagnetism work?

Ans. Palaeomagnetism works by analyzing the magnetic properties of rocks, which can capture the direction of Earth's magnetic field when they formed. This provides a record of how Earth's magnetism has shifted.

Q3. Why is palaeomagnetism significant?

Ans. Palaeomagnetism is significant because it gives insights into past geographical changes, helps predict future magnetic field shifts, and provides evidence of Earth's geological evolution. It also supports the theory of plate tectonics by showing how the ocean floor is continuously created and moved.

Q4. How does palaeomagnetism support the theories of sea-floor spreading and plate tectonics?

Ans. Palaeomagnetism shows that as magma rises at mid-ocean ridges and solidifies, minerals align with Earth's magnetic field, creating symmetrical polarity stripes on the ocean floor. This evidences continuous oceanic crust creation and supports plate tectonics by dating plate movements and sea-floor spreading.