In a new paper published this month, National Science Foundation-funded researchers offered an answer to one of Earth science's fundamental questions: Where do continents form? The mantle is Earth's thickest layer, spanning about 1,800 miles between the planet's core and its thin outer crust. Earth scientists believe that little, if anything, moves between the mantle and core, but the mantle and everything above it -- seafloor, oceans, continents and atmosphere -- are connected, and many of the atoms on Earth's surface today, including the atoms in humans and other living things, have cycled through the mantle one or more times in Earth's 4.6 billion years. The rocks in continents are an exception. Geologists have found some that are up to 4 billion years old, which means they were formed near the surface and stayed on the surface, without being recycled into the mantle. That's due in part to the nature of continental crust, which is far less dense than the basaltic rocks beneath Earth's oceans. It's no coincidence that Earth is the only rocky planet known to have both continents and life.
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