( ( ( The source ) ( of ( geothermal power ) ) ) ( ( is ( ( the heat ) ( contained ( inside ( the Earth ) ) ) ) ) ; ) )
(ROOT (S (NP (NP (DT The) (NN source)) (PP (IN of) (NP (JJ geothermal) (NN power)))) (VP (VBZ is) (NP (NP (DT the) (NN heat)) (VP (VBN contained) (PP (IN inside) (NP (DT the) (NN Earth)))))) (: ;)))
The source of geothermal power is the heat contained inside the Earth;
(ROOT (S (NP (JJ Geothermal) (NN power)) (VP (VBZ is) (VP (VBN generated) (PP (IN via) (NP (NP (JJ underground) (NNS sources)) (PP (IN of) (NP (NN heat))))))) (. .)))
Geothermal power is generated via underground sources of heat.