Some people toughen under increased pressure. Some rocks do too. Squeezing a common, iron-bearing mineral at the hellish pressures deep within our planet makes the material much stiffer than geophysicists had expected. This response may explain why seismic waves travel particularly fast through some deep zones of rock, say the researchers who performed the experiment.
The lower mantle, a thick region of Earth's inner structure, lies just outside the planet's core. Using vibrations from earthquakes as probes, scientists have detected large volumes of lower-mantle material where seismic waves travel m