3.  Gravitational Contraction ◦ Gravity pulled Earth’s center together causing friction that released heat energy. ◦ This thermal energy is left over from the formation of Earth.

5.  Radioactivite Elements Decaying ◦ Heavy elements in Earth’s core give off heat energy as they break down. ◦ Uranium and potassium (isotopes).

8.  Radiation ◦ The transfer of thermal energy by electromagnetic waves. ◦ Radioactive elements in Earth’s core transfer thermal energy to the matter around them through radiation.

10.  Conduction ◦ The transfer of thermal energy between objects that touch.  Solids ◦ Conduction occurs between the metals of the inner core and the rocks in the crust.

12.  Convection ◦ The transfer of thermal energy by the movement of heated material from one place to another.  Liquids and gasses ◦ Convection occurs in the liquid outer core and the semi-liquid mantle.

14.  The transfer of thermal energy and matter through the mantle.  Hotter parts of the mantle become less dense and rise.  Cooler parts of the mantle become more dense and sink.

18.  The thermal energy from radioactivity in Earth’s core powers convection currents in the mantle.

19.  Energy and matter are continuously transferred through Earth’s interior. ◦ Thermal energy ◦ Radioactive energy ◦ Seismic waves