Earth's magnetic field is powered by a swirling ocean of molten iron and nickel as hot as the Sun's surface.

The Earth's outer core is a layer of liquid iron and nickel roughly 2,260 kilometers thick. It begins approximately 2,890 kilometers beneath the surface. Temperatures here range from 4,500 to 5,500 degrees Celsius, which is comparable to the 5,505 degree Celsius surface of the Sun. This intense heat is maintained by the decay of radioactive elements and residual heat from Earth's formation 4.5 billion years ago.The geodynamo theory explains how the magnetic field is sustained. As the Earth rotates, the Coriolis effect causes the molten metal to swirl in helical patterns. This kinetic energy transforms into magnetic energy through electromagnetic induction. This process was first mathematically described by physicist Walter Elsasser in the 1940s. His work laid the foundation for modern geophysics.This magnetic field extends tens of thousands of kilometers into space, forming the magnetosphere. It acts as a vital barrier against the solar wind, which consists of charged particles from the Sun. Research from NASA's MAVEN mission suggests that Mars lost its atmosphere because its internal core cooled and its magnetic field failed. This comparison highlights why Earth's active core is essential for supporting life and liquid water.