Earth’s Core Is About 2.5 Years Younger Than Its Surface

Gravity makes time pass slightly slower deep inside Earth, leaving the core about 2.5 years younger than the surface after 4.5 billion years.

Physics

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Earth does not experience time at exactly the same rate everywhere. General relativity predicts that clocks deeper in a gravitational field tick slightly more slowly than clocks farther away. Because Earth has a huge amount of mass, this effect exists between its interior and its surface. The difference is extremely tiny from moment to moment, but Earth has existed for roughly 4.5 billion years, so the small rate difference adds up. Calculations that account for Earth’s changing density put the accumulated difference between the core and surface at about 2.5 years, with the core being younger. This does not mean the core formed later. The planet formed and evolved as a whole, while different locations experienced slightly different rates of elapsed time. The same basic effect is important in real technology: highly accurate clocks at different gravitational potentials do not tick at exactly the same rate, so relativistic corrections are needed in systems such as satellite navigation.

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