Why are most rocks on Earth much younger than the planet itself?

The rocks on Earth are not all the same age. In fact, most are significantly younger than the planet itself. The oldest sections of the oceanic crust are thought to be 200 million years old—a blink of an eye in the planet's billion-year lifespan. What is going on here? "Earth is an active planet," explains Boyet, a geochemist at the University of Clermont Auvergne in France. "This makes it different to other planets in our solar system, as well as to our moon."

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