Magma ocean

[1] A prime example would be the Moon-forming impact on Earth, that is thought to have formed a magma ocean with a depth of up to 2000 km.

[1] The findings of the Apollo missions were the first articles of evidence to suggest the existence of a magma ocean on the Moon.

[1] This discovery gave rise to the hypothesis that the rocks formed through an ascension to the surface of a magma ocean during the early life stages of the Moon.

[1] Additional evidence for the existence of the Lunar Magma Ocean includes the sources of mare basalts and KREEP (K for potassium, REE for rare-earth elements, and P for phosphorus).

[1] The existence of these components within the mostly anorthositic crust of the Moon are synonymous with the solidification of the Lunar Magma Ocean.

[1] Unlike Earth, indications of a magma ocean on the Moon such as the flotation crust, elemental components in rocks, and KREEP have been preserved throughout its lifetime.

Full volcanic planet, magma ocean in surface
The formation of the lunar magma ocean which was a layer of molten rock believed to measure hundreds of kilometers in depth. [ 1 ]