At long last, ocean drillers exhume a bounty of rocks from Earth’s mantle

In 1961, geologists off the Pacific coast of Mexico embarked on a daring journey to a foreign land—the planet’s interior. From a ship, they aimed to drill through the thin veneer of Earth’s crust and grab a sample of the mantle, the 2900-kilometer-thick layer of dense rock that fuels volcanic eruptions and makes up most of the planet’s mass. The drill only got a couple hundred meters below the seabed before the project foundered under spiraling costs. But the quest—one of geology’s holy grails—remained.