What evidence do we have that our planet was once a molten mass and that it continues to release heat today?

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.

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Ithink i might know wait one second let me serve