The correct answer is Mantle Explanation & Key Takeaways: • The main source of magma is the upper part of the mantle, particularly the asthenosphere: • Asthenosphere • This layer is located in the upper mantle, beneath the lithosphere, and is made up of semi-fused and solid materials. • It's considered the main source of magma that reaches the surface during volcanic eruptions. • Magma • Magma is a mixture of molten or semi-molten rock, volatiles, and solids. • It's produced when the mantle or crust melts in various tectonic settings, such as continental rift zones, mid-ocean ridges, subduction zones, and hotspots. • The Earth's core is a major energy source for the planet. • It stores energy from radioactive decay and core-mantle segregation, and produces heat as the inner core continues to grow. Related Concepts: • Crust • The crust is made of solid rock, mostly basalt and granite. • There are two types of crust: oceanic and continental. • Oceanic crust is denser and thinner, while continental crust is thicker and less dense. • Inner core • The inner core is made of extremely hot metal, mostly iron and nickel, under incredible pressure. • The pressure is so high that it prevents the iron from melting, making the inner core solid. • Outer core: The third layer, located about 1,800 miles below the crust