Earth's magnetic field
Heat escapes from Earth's core at a rate of about 47 terawatts. This energy drives convection currents in the liquid outer core, which extends to roughly 3400 kilometers below the surface. The outer core consists of molten iron and nickel alloys that flow continuously. These flows generate electric currents through a process known as the geodynamo. A feedback loop sustains this system: current loops create magnetic fields while changing magnetic fields induce electric currents. The Coriolis effect organizes these fluid motions into rolls aligned along the north-south polar axis. Without this motion, the dipole part of the field would vanish within tens of thousands of years. Scientists calculate the average magnetic field inside the outer core to be 25 gauss. That value is fifty times stronger than the field measured at the surface.
Charged particles leave the Sun's corona at speeds between 200 and 1000 kilometers per second. These streams form the solar wind and carry their own magnetic field called the interplanetary magnetic field. Earth's magnetosphere deflects most of these particles before they reach the atmosphere. The boundary where pressures balance is called the magnetopause. On the sunward side, this boundary sits about 10 Earth radii away. The opposite side stretches beyond 200 Earth radii into a long magnetotail. Inside this region lies the plasmasphere, a donut-shaped zone containing low-energy plasma. Two concentric tire-shaped regions called Van Allen radiation belts hold high-energy ions. Astronauts on the Moon risk lethal radiation exposure during violent solar eruptions. A particularly strong event in 2003 damaged more than one-third of NASA's satellites.
Evidence for past polarity flips exists in basalts and sediment cores taken from ocean floors. Reversals occur nearly randomly with intervals ranging from less than 0.1 million years to as much as 50 million years. The most recent geomagnetic reversal occurred approximately 780,000 years ago. This event is known as the Brunhes-Matuyama reversal. During an excursion, the dipole axis crosses the equator and returns to its original polarity. The Laschamp event took place 41,000 years ago during the last ice age. Magnetic minerals like magnetite record these changes when lava flows cool or sediments settle. New basalt records the reversed direction as it forms along mid-ocean ridges. Ships towing magnetometers detect symmetric stripes that reveal the age of the ocean floor below. Radiometric dating helps establish a geomagnetic polarity time scale used by geophysicists today.
Over the last two centuries, the dipole strength has decreased at a rate of about 6.3% per century. The North Magnetic Pole migrates northwestward across the Arctic landscape. In 1831, this pole sat near Cape Adelaide in the Boothia Peninsula. By 2001, it had moved to coordinates near Resolute Bay. Movement rates reached up to 55 kilometers per year in 2003. A westward drift occurs at roughly 0.2 degrees per year globally since around 1400 AD. Between 1000 AD and 1400 AD, the average drift was eastward instead. Scientists analyzed simulations showing maximum directional change rates reaching approximately 10 degrees per year. This speed is nearly one hundred times faster than current changes. Data from the THEMIS mission indicates field reduction when magnetic orientation aligns between Sun and Earth. Such alignment could cause blackouts during future solar storms affecting artificial satellites.
Carl Friedrich Gauss measured Earth's magnetic field strength for the first time in 1832. Modern measurement relies on satellites like Ørsted and CHAMP alongside ground-based observatories. The International Real-time Magnetic Observatory Network records data from over 100 interlinked stations worldwide since 1991. Governments operate units specializing in field measurements such as the British Geological Survey's Eskdalemuir Observatory. These facilities forecast magnetic conditions that sometimes disrupt communications or electric power grids. Military aircraft fly instruments called magnetic anomaly detectors to find submerged submarines. Commercial companies use these tools to identify ore bodies like the Kursk Magnetic Anomaly. Mathematical models convert discrete measurements into global predictions. The International Geomagnetic Reference Field updates every five years using spherical harmonics. The latest version includes 195 coefficients derived from satellite and observatory data. Researchers can now estimate field conditions back to the year 1590 using ship logs.
Animals including birds and turtles detect Earth's magnetic field to navigate during migration. Some researchers observed cows and wild deer aligning their bodies north-south while relaxing. This behavior disappears when animals stand under high-voltage power lines. European robins rely on a magnetic compass disrupted by weak electromagnetic fields between 2 kHz and 5 MHz. AM radio signals and ordinary electronic equipment generate frequencies that interfere with bird navigation. Neither cellphone signals nor power lines cause this specific disruption. Bacteria also utilize magnetoreception for orientation within their microscopic environments. Scientists study how these biological systems interact with natural background fields. Understanding these mechanisms helps explain why certain technologies affect animal behavior differently than expected.
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Common questions
What generates Earth's magnetic field and how does it work?
Convection currents in the liquid outer core generate electric currents through a process known as the geodynamo. This system consists of molten iron and nickel alloys flowing continuously to create a self-sustaining feedback loop between current loops and magnetic fields.
How far does Earth's magnetosphere extend from the planet on the sunward side and opposite side?
The boundary where pressures balance called the magnetopause sits about 10 Earth radii away on the sunward side. The opposite side stretches beyond 200 Earth radii into a long magnetotail containing the plasmasphere and Van Allen radiation belts.
When did the most recent geomagnetic reversal occur and what is its name?
The most recent geomagnetic reversal occurred approximately 780,000 years ago and is known as the Brunhes-Matuyama reversal. Reversals happen nearly randomly with intervals ranging from less than 0.1 million years to as much as 50 million years.
Where was the North Magnetic Pole located in 1831 and how fast has it moved recently?
In 1831 this pole sat near Cape Adelaide in the Boothia Peninsula before moving to coordinates near Resolute Bay by 2001. Movement rates reached up to 55 kilometers per year in 2003 while global westward drift occurs at roughly 0.2 degrees per year since around 1400 AD.
Who measured Earth's magnetic field strength for the first time and when did they do it?
Carl Friedrich Gauss measured Earth's magnetic field strength for the first time in 1832. Modern measurement relies on satellites like Ørsted and CHAMP alongside ground-based observatories that record data from over 100 interlinked stations worldwide since 1991.