Inner vs. Outer Core: Earth’s Molten Heart vs. Solid Dynamo Explained
The inner core is a solid iron-nickel sphere at Earth’s center, reaching ~5,400 °C. The outer core is its liquid iron-nickel shell that swirls and generates our magnetic field.
People hear “core” and picture one hot blob. Because both layers are scorching, they assume both are liquid. The surprise: the inner core stays solid under crushing pressure, while the outer core remains fluid—sparking the mix-up.
Key Differences
Inner core: solid, 1,220 km radius, 5,400 °C, spins slightly faster. Outer core: liquid, 2,260 km thick, 4,000–6,000 °C, creates magnetism. One anchors; the other dances.
Which One Should You Choose?
You can’t pick—both are vital. Without the solid inner core’s stability and the outer core’s motion, Earth would lack a magnetic shield, letting solar wind strip our atmosphere.
Examples and Daily Life
Your phone compass and aurora selfies rely on the outer core’s flow. GPS satellites dodge space radiation thanks to the magnetic bubble powered by that same molten dynamo.
Could the inner core melt?
Only if pressure drops—say, a cosmic impact removes overlying mass—then it could liquefy, collapsing the magnetic field.
How do we know the outer core is liquid?
Seismic waves called S-waves stop at the outer core, proving it’s fluid, while P-waves slow but pass through.