Geologists have long wondered about the temperature of Earth’s mantle—the thick layer of rock that stretches from 20 to 1,800 miles underground, sandwiched between the core and crust of the planet. Sticking a thermometer to that depth hasn’t exactly been feasible, so researchers have used indirect methods. This year two geophysicists announced they may have found the answer in the barrel of a gun.
Kathleen Holland of Sandia National Laboratories and Thomas Ahrens of Caltech put pieces of olivine—a translucent gem—into an apparatus that is essentially a sealed giant high-powered cannon. They fired projectiles at the olivine at velocities up to four miles a second, creating a brief shock wave so intense it transformed the crystal structure of the olivine into two minerals thought to be major ingredients of the mantle—magnesiowüstite and perovskite. Seismic-wave data suggest that the lower mantle is partially molten, so the researchers blasted the rock to ...
