Final answer:
Some layers of Earth are liquid while others are solid due to the interplay of temperature and pressure, with the core, mantle, and crust being affected differently by these factors.
Step-by-step explanation:
The reason why some layers of Earth are liquid and some solid can be attributed to the interplay of both temperature and pressure inside Earth. Substance state, whether solid, liquid, or gas, is the result of a balance between the particles' energy and the forces between them. This is strongly influenced by temperature, as it determines the energy of the particles. Therefore, the correct answer is a) because of the interplay of temperature and pressure.
Specifically, Earth's interior is divided into the core, mantle, and crust based on chemical composition, and into the lithosphere and asthenosphere based on mechanical properties. The solid inner core is under incredible pressure and composed of an iron and nickel alloy, while the outer core is liquid and generates Earth's magnetic field. The mantle behaves plastically and can deform, indicating a semi-solid state. The Earth's crust, which is solid, includes both continental and oceanic types and is the outermost layer.
Temperature and pressure differences within Earth facilitate the existence of both solid and liquid layers. The solidus line in a Pressure and Temperature graph of crustal rocks illustrates the conditions under which rocks transition from solid to liquid states.