<p>Good Acoustics The mystery of two continent-sized structures buried deep in the Earth's mantle has produced a new twist after scientists got a closer look at their composition, suggesting they might be even older than once thought. Well, a closer listen may be more accurate. "When there is a big earthquake, the whole Earth will expand and contract like a bell," Arwen Deuss, a seismologist at Utrecht University in the Netherlands and coauthor of a new paper published in the journal Nature, told New Scientist. "Earth becomes a musical instrument." And like an instrument, you can tell a lot about […]</p>