Drilled Core Exposes Previously Unseen Layer of Earth's Crust

Since the 1950s, scientists have been trying to drill through the oceanic crust to expose the mantle below. Although that goal remains out of reach--the crust is more than four miles thick--a new drilling project at the bottom of the Pacific Ocean has reached almost a mile below the sea-floor and exposed what lies beneath the uppermost layer of crust for the first time.