1. Which layer is made up of liquid iron? A. crust B. inner core 2. What is the heat source for convection currents? A. inner core B. crust C. asthenosphere 3. About 80% of Earth's volume is found in this layer called A. crust B. outer core C. inner core 4. What does "molten" mean? A. liquid B. gas C. solid D. hot 5. All of the elements are commonly found in the Earth's crust EXCEPT A. oxygen B. calcium C. silicon C. outer core D. mantle D. mantle D. mantle D. iron​