in what part of the earths internal structure can rocks melt
Structure of the Earth The average density of Earth is 7000551499999999999♠5.515 g/cm3.[8] Because the average density of surface material is only around 7000300000000000000♠3.0 g/cm3, we must conclude that denser materials exist within Earth's core. This result has been known since the Schiehallion experiment, performed in the 1770s. Charles Hutton in his 1778 report concluded that the mean density of the Earth must be about     9 5   {\displaystyle {\tfrac {9}{5}}}  that of surface rock, concluding that the interior of the Earth must be metallic. Hutton estimated this metallic portion to occupy some 65% of the diameter of the Earth.[9] Hutton's estimate on the mean density of the Earth was still about 20% too low, at 7000450000000000000♠4.5 g/cm3 Henry Cavendish in his torsion balance experiment of 1798 found a value of 7000545000000000000♠5.45 g/cm3, within 1% of the modern value.[10] Seismic measurements show that the core is divided into two parts, a "solid" inner core with a radius of ≈1,220 km[11] and a liquid outer core extending beyond it to a radius of ≈3,400 km. The densities are between 9,900 and 12,200 kg/m3 in the outer core and 12,600–13,000 kg/m3 in the inner core.[12]