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About 4.5 billion years agoReputable source · 2 sourcesWell documented

Earth settles into a layered core and a magnetic shield

On the timeline · around About 4.5 billion years ago · The Hadean EarthBuilding the PlanetsThe Hadean EarthEarth settles into a layered core and a magnetic shield4.5 Ga4.5 Ga4.5 Ga4.4 Ga4.4 Ga4.4 Ga

What happened

Heated by its own accretion and by the giant impact, the young Earth settled into the layers it still has: a solid inner core and a molten outer core of iron and nickel, a thick rocky mantle, and a thin crust. NASA puts the solid inner core at about 1,220 kilometres in radius, wrapped in a liquid outer core roughly 2,300 kilometres thick. That churning liquid metal, driven by heat leaking out of the core and twisted by Earth's spin, runs as a geodynamo: it sets up electric currents that produce Earth's magnetic field, which reaches out into space as the magnetosphere.

Why it matters

The magnetosphere shields the atmosphere from the solar wind, the stream of charged particles the Sun constantly throws off, which would otherwise strip the air away over time. Stable air and oceans are far harder to keep on a rocky planet with no magnetic shield, so this layering is part of what kept early Earth habitable.

How we know

NASA gives the iron-and-nickel core in its measured dimensions and ties Earth's magnetic field directly to that rotating molten core. The magnetosphere the field creates is not merely inferred, it is mapped, flown through and measured by spacecraft.

Sources

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Part of a timelineThe Formation of the Solar System11 events · The 800 million years that turned a collapsing cloud of gas into the Sun, the planets, and a habitable Earth, from the oldest solids we can date to the first oceans.View all →
Earth settles into a layered core and a magnetic shield · The Formation of the Solar System · SourcedStory