The Earth's Magnetic Field is generated by a mechanism called the "geomagnetic dynamo" occurring in the liquid outer core, composed of iron and nickel. The Earth's magnetic field can be roughly represented as that of a magnetic dipole, with a north pole and a south pole, forming the magnetosphere, a protective bubble around the planet.
The intense heat from the solid inner core (at about 6,000 K) generates a heat flux that causes thermal convection movements in the liquid outer core. It is the temperature difference between the inner and outer core that drives these convection movements. Hotter liquid metals rise while cooled elements sink, creating convection cells. This process occurs like in a pot of water on a heating plate, where the heat from the bottom of the pot creates convection currents in the water: heated water near the bottom rises to the surface while cooler water descends.
Due to the Coriolis effect from the Earth's rotation around its axis, the convection cells follow helical trajectories. Thanks to the influence of Earth's rotation, chaotic and turbulent movements follow certain major lines. The Coriolis force tends to align these convection movements into columns parallel to the Earth's axis of rotation. This alignment promotes a global organization of currents that allows a collective alignment of the magnetic field preferentially oriented along the Earth's rotation axis. This helps align and stabilize the magnetic field along an approximately north-south axis.
Furthermore, the movements of the liquid metal, which is conductive, generate electric currents that, in turn, create a magnetic field. This link between the movement of magnetic fields and the generation of electric currents creates what is known as electromagnetic induction. This positive feedback phenomenon amplifies the field until it reaches a stable (though fluctuating) configuration that constitutes the Earth's magnetic field.
Iron-containing minerals in volcanic and sedimentary rocks preserve the orientation of the Earth's magnetic field at the time of their formation, serving as paleomagnetic markers. By analyzing these rocks, geophysicists have been able to reconstruct a timeline of inversions, known as the magnetic chronology. These records show that the frequency of inversions varies widely over geological ages.
• The last magnetic polarity inversion, known as Brunhes-Matuyama, occurred about 780,000 years ago, marking the transition to the current normal polarity.
• The Olduvai inversion occurred about 1.8 million years ago.
• The Matuyama-Gauss inversion occurred about 2.58 million years ago.
• The Gauss-Gilbert inversion occurred about 3.6 million years ago.
• During the Cretaceous, polarity remained constant for about 40 million years (83 to 125 million years). This exceptional period of magnetic stability is called the "Cretaceous Normal Superchron".
• Another superchron, the Kiaman Superchron (Carboniferous - Permian, about 262 to 318 million years ago), but with an inverse polarity that remained constant for about 56 million years.
Plate Tectonics: The Invisible Engine Moving the Continents 
The Mystery of the Number 360: When Earth Imposes Its Geometry on the Circle 
Wet-Bulb Temperature: Humanity's Climate Time Bomb 
The Sky Ordered Our Week: Monday, Tuesday, Wednesday... 
Why Doesn't Earth's Atmosphere Escape into Space? 
Origins of Earth: Magmatic Chaos and the Birth of the Solid World 
Earth's Atmosphere: The Invisible Shield Protecting Life 
The Three Ages of Terrestrial Water: Multiple Origins 
From Carbon 14 to Uranium-Lead: The Science of Dating 
The Boundary of Space: Where Does It Really Begin? 
The Leap Second 
Planetary Alignments: A Fascinating but Relative
Phenomenon 
All Deserts of the World 
Earth's Paleoclimates and Carbon Dioxide 
Three Gorges Dam and Day Length 
International Date Line 
Start Date of the Seasons: A Complex Celestial Mechanism 
Reversal of the Earth's magnetic field over time 
3D Simulator: Revolutions of the Planets 
Geological Time and Mass Extinctions: From the Ordovician to the Cretaceous 
Earth History: Timeline Compressed into 24 Hours 
Earth's Water: An Extraterrestrial Origin? 
Reading the Sky: Understanding Declination and Right
Ascension 
Inversions of the Earth's Magnetic Field 
Earth's Magnetosphere: The Invisible Shield 
Fujita Scale: Classifying the Fury of Tornadoes 
Earth's Radioactivity: The Internal Energy of Our Planet 
The Deep Sea: Exploring the Deepest Ocean Trenches 
Why Are Days Getting Longer? 
The Depths of the Earth: From the Lithosphere to the Core 
Earth's Movements: How Earth Traces Its Spiral Through the Universe? 
How much is the sea level rising? 
The Life of Earth: Structure and Layers of the Earth 
The Eccentricity of Earth's Orbit: An Ellipse That Changes
Everything 
Little Ice Age: The History of a Natural Climatic Cooling 
The Quest for Time: How Ancient Civilizations Used
Astronomy? 
Van Allen Radiation Belt: A Shield Against Cosmic Particles 
Axis of rotation of the planets or obliquity 
The Cosmos in Our Measure: When Man Invents the Universe 
The Galilean Cut 
What is the pendulum fixed relative to? 
Problem of longitude at sea 
World population, still gallopingin 2008 
The Oldest Image of Earth from Space 
Earth's Obliquity and Variations in Its Axis of Rotation 
The Astronomical Unit Fixed: A Length, No Longer an Orbit 
One Molecule, Three States: Solid, Liquid, Gas on a Single Planet 
Simulator, the round of near-Earth cruisers 
Satellites that measure underwater relief 
Hadean's Hell 
The First Free Flight of an Astronaut in Space 
The first measurement of the Earth-Sun
distance 
La The Announced End of the World on December 21, 2012: A Millennial
Prophecy
The Equinoxes: An Astronomical Event
Milankovitch Cycles: The Astronomical Rhythm of Earth's Climate