The center of Earth is younger than the outer surface
Our home planet is young at heart. According to new calculations, Earth’s center is more than two years younger than its surface.
In Einstein’s general theory of relativity, massive objects warp the fabric of spacetime, creating a gravitational pull and slowing time nearby. So a clock placed at Earth’s center will tick ever-so-slightly slower than a clock at its surface. Such time shifts are determined by the gravitational potential, a measure of the amount of work it would take to move an object from one place to another. Since climbing up from Earth’s center would be a struggle against gravity, clocks down deep would run slow relative to surface timepieces.
Over the 4.5 billion years of Earth’s history, the gradual shaving off of fractions of a second adds up to a core that’s 2.5 years younger than the planet’s crust, researchers estimate in the May European Journal of Physics. Theoretical physicist Richard Feynman had suggested in the 1960s that the core was younger, but only by a few days.
The new calculation neglects geological processes, which have a larger impact on the planet’s age. For example, Earth’s core probably formed earlier than its crust. Instead, says study author Ulrik Uggerhøj of Aarhus University in Denmark, the calculation serves as an illustration of gravity’s influence on time — very close to home.