No, not all magma comes from the Earth's core. While the core is a source of heat that drives the process, most magma actually originates from the Earth's mantle, specifically from the asthenosphere.

Here's why:

* The Earth's core is incredibly hot and dense: The pressure and temperatures are so extreme that the core is primarily composed of solid iron and nickel, with a liquid outer core. While the core provides the heat source, the extreme conditions don't allow for large-scale melting.

* The asthenosphere is a partially molten layer: This layer within the upper mantle is hot enough to allow for some rock to melt. This molten rock, called magma, can then rise towards the surface.

* Magma formation in the asthenosphere: Melting in the asthenosphere is primarily driven by a decrease in pressure as rock rises. This process is known as decompression melting. Additionally, the presence of water and other volatiles can lower the melting point of rocks.

In summary:

* The Earth's core provides the heat source for magma formation.

* Most magma originates in the asthenosphere, a partially molten layer in the upper mantle.

* Magma formation in the asthenosphere is primarily caused by decompression melting and the presence of volatiles.

While some extremely deep magma sources may be related to interactions with the core, these are exceptions, and most magma originates within the mantle.