Most of the Earth’s volume is contained in the mantle, a rocky layer 2,970 kilometres (1,845 miles) thick, sandwiched between the planet’s core and crust. Despite temperatures approaching 4,300 degrees Celsius (7,772 degrees Fahrenheit) near the core, most of the mantle is solid due to the huge pressure it is under. Earthquakes are an important source of information about what lies beneath our feet. By studying how seismological waves spread through the planet, geologists can deduce its structure. Certain waves, for example, can’t travel through liquids, leading scientists to conclude that the planet’s outer core is liquid.